Re: An amateur estimate of the apparent brightness in magnitudes of the LCROSS impact ejecta curtain

[Arnold Ashcraft]

Kurt:
Thanks for going through this calculation. It gives me a lot more
confidence about our results when I see that your calculations and
mine, although going by way of a completely different path, come
up with essentially the same prediction: that the exposures required
will be comparable to those we have been using for familiar objects
like the moon itself and planets like Mars and Saturn. I had planned
to set my webcam at an exposure which gave a nearly fully saturated
image for the brighter portions of the moon's limb and to trust that the
impact plume would also be imaged with sufficient density to give a
good photographic record. That is essentially what one must do to
record a planet emerging from the illuminated lunar limb. I will be
using my DMK31 camera, no filters, 2x Barlow and my 7.25" f/14
Schupmann medial with an exposure up to about 1/25th of a second.
This departs from my usual conditions for lunar imaging in that I
normally use a combination of a #25 red filter and NIR blocking
filter to minimize seeing related problems. The peak brightness of
the plume in the middle of the visible spectrum is what made me
decide to not use the filters. I don't want to throw away any of the
light from the plume.

Recording the ionized OH cloud (assuming there is water vapor
in the impact plume) will take more exposure. To get this also, I plan
to have my SBIG ST-8 working at the f/6 focus of my 12.5" Newtonian
taking short time exposures during and after the impact. Hopefully,
the same conditions that let me record the expanding gas cloud around
comet Holmes last year will suffice for the ionized gas cloud around
the impact plume. A friend of mine has volunteered to operate one
of the cameras for me. Now if we can only get Murphy on our team
as well, we might get some images! ;-)

Clif

On Dec 13, 2008, at 12:04 AM, cano...@yahoo.com wrote:

>
> I decided to take a stab at quantifying what the likely brightness of
> the Centaur booster will be and the perimeters of likely camera
> settings to capture the impact's ejecta curtain. I'm no physics wiz
> and I don't know if the following is correct, but here it goes. Even
> if this estimate turns out to be significantly wrong, hopefully it
> will stimulate further discussion on this topic.
>
> Previously, by examining the December imaging session photos posted
> here, we concluded that the impact under all likely scenarios except a
> small 4 to 5km high ejecta curtain, was large enough to capture with
> amateur imaging equipment. This post asks the question of whether the
> ejecta curtain will reflect enough sunlight towards Earth based
> amateurs to be seen visually and/or to be picked up on amateur CCD
> imagers.
>
> Corrections and criticisms to any of the following are welcomed and
> appreciated. Hopefully it is in ballpark and not completely off base.
> While I feel good about the computation - the result intutitively
> seems too bright to me.
>
> The addendum to this post includes most of the math computations, with
> one exception as noted in the addendum.
>
> The starting point is slide 18 in the LCROSS Team May AAS presentation
> reciting a spectral radiance for the ejecta curtain of a maximum of 40
> Watts str^-1 m-^2 micron^-1 at around 550 nanometers - probably based
> on an ejecta curtain of between 5 to 10 km tall. This spectral
> radiance is assumed to be the radiance for an Earth based observer and
> not an average value at the impact site. The approach taken here is to
> convert that spectral radiance into visual magnitudes per arcsec and
> to then look for guidance in analogous visual and amateur
> astrophotography imaging. Clif worked a separate computation based on
> the flux needed to fill the wells of his CCD imaging chip.
>
> The ending conclusion is that the brightness of the impact for Earth-
> based amateurs will be similar to imaging Mars as it egresses from the
> bright limb of the Moon. In terms of magnitudes per square arcsquare
> (MPSAS), reasonable image planning perimeters for the brightness of
> the impact ejecta curtain are between 2.6 to 3.9 MPSAS. The range of
> 2.6 to 3.9 MSPAS for the curtain brightness was based on artibrarily
> assuming that the radiance would decrease from 40, 30, 20 and 10 W
> str^-1 m^-2 micron^-1. (For 1 W str^-1 m^-2 micron^-1, the conversion
> result is 6.2 MPSAS outside the atmosphere.)
>
> Based on the above, the following table summarizes a spread of
> possible MPSASs and diameters for various kilometer heights of the
> ejecta curtain at an average distance of 384400 km from the observer:
>
> Height
> km | MPSAS | Dia arcsec | v~ at 3.9 MPSAS
>
> 05 2.2-3.9 2.6 --
> 10 2.2-3.9 8.4 -0.6
> 20 2.2-3.9 10.7 -0.9
> 30 2.2-3.9 16 -3.2
>
> The following lists values for the brightness and size of planets all
> of which have been easily imaged by amateurs egressing from the bright
> limb of the Moon:
>
> Planet | MPSAS | Dia arcsec | v
> Saturn 6.7 14-20 0.4 to 1.2
> Jupiter 5.3 30-50 -1.6 to 2.9
> Mars 4.0 3.5-25 -2.9 to 1.8
> Venus 1.5 9.7-6.6 up to -4.6
>
> Integrated magnitudes (v) of -0.6 to -3.2 and their relative MPSASs of
> 2.2-3.9 seem awfully high to me, but they should be interpreted in the
> context of the bright lunar surface. Recall that most Earth based
> amateur lunar images have no stars in them - a feature also seen in
> Apollo astronaut images taken from the surface of the Moon. This is
> because the illuminated lunar surface is so bright and the exposure
> times so short, that the stars are never exposed for a sufficient time
> to appear on the image. The following are average MPSASs for Moon
> targets derived from the appendix to Covington's _Astrophotography for
> Amateurs_ as:
>
> MPSAS | Lunar target type
> 3.4 Moon full
> 3.9 10 minutes after sunset
> 4.5 Moon gibbous
> 5.3 Moon quarter terminator objects
> 6.1 Moon wide crescent
> 6.8 Moon narrow crescent
>
> In summary, what the above says is similar to what Clif and Jim Mosher
> have previously concluded: the apparent brightness of the ejecta
> curtain, as it reflects sunlight to be somewhat similar in brightness
> to the Moon's surface, e.g. an MPSAS of 4.0 for the ejecta curtain as
> compared to first and third quarter lunar terminator objects of 5.3
> MPSAS. Clif suggested that this reasoning follows from the fact that
> the ejecta curtain will be composed of a large volume of the lunar
> surface. (Albeit that the material will be atomized and spreadout over
> a much larger surface area and at a lower density than at is occurs
> naturally on the lunar surface.)
>
> Imaging Mars as it egresses the bright lunar limb is probably the best
> analogy. A high-bound imaging setting might be those that you use to
> image Mars; low-bound conservative settings would be to use those for
> imaging Saturn (6.7 MPSAS) or Uranus (8.6 MPSAS). The low-bound
> estimate would overexpose the Moon's surface but have a greater chance
> of capturing the impact; the high-bound estimate would expose the
> surface properly but risk missing capture of the ejecta curtain's
> light.
>
> Examples of successful amateur imaging of the above planets egressing
> the bright lunar limb, quickly garnered from the internet, include:
>
> Saturn
> http://antwrp.gsfc.nasa.gov/apod/ap970924.html
> http://www.space.com/spacewatch/occult_pics_020221.html
>
> Jupiter
> http://www.occultations.net/
>
> Mars
> http://www.iucaa.ernet.in/~scipop/Sky/mars_occultation08.htm
>
> Venus
> http://www.iucaa.ernet.in/~scipop/Sky/venus_occultation.htm
>
> The 40 W str^-1 m^-2 micron^-1 radiance value is a one-shot maximum
> estimate. It will change and dim based on two principal factors.
>
> First, the maximum brightness will dim as the ejecta curtain
> expands.
>
> Second, what might be seen may vary from the one-shot maximum estimate
> based on the geocentric angle between the observer and impact. The
> one-
> shot maximum reflectance of 40 Watts str^-1 m-^2 micron^-1 assumes an
> optimal viewing angle for the reflected light - usually a normal 90
> degree right-angle view of the emitting surface - the ejecta curtain
> in this case. If the observer-target-sun angle departs significantly
> from the normal view optimum, the reflected light will dim by the
> inverse of the cosine of the observer-target-sun (O-T-S) angle. (The
> Dec. 6-8 imaging sessions were at a near normal O-T-S angle of about
> 87 degrees.) The amount of sunlight reflected by the lunar dust will
> vary by the Observer-Target-Sun angle. With the zodical light,
> interplanetary dust is best seen when the 3-D ecliptic plane is tilted
> about 60 degrees with respect to the observer's latitude. An analogy
> to the effect of the Sun angle is that features made of the lunar
> reoglith on the Moon's surface as seen in the eyepiece vary in
> brightness based on the angle of solar illumination. A sixty degree
> optimal angle for the LCROSS impact is also mentioned in the May 2007
> AAS presentation with respect to the LCROSS sheparding satellite's
> view of the impact.
>
> The topocentric O-T-S angle does not change appreciably for any single
> event between let's say Denver and Buenos Aires.
>
> But as the ejecta curtain expands, it will change shape and alter the
> Observer-Sun-Target angle between the local parts of the ejecta
> curtain's surface and the observer. That change, which probably
> cannot be predicted, may result in favoring some observers at north vs
> south geographic latitudes with relatively brighter images of the
> target.
>
> The process of determining the Observer topocentric - Target - Sun
> angle is outlined in part in Dr. Wooden's 11/29/2008 post titled
>
> Lunar Crater Ephemerides with Horizons (using web interface
> http://ssd.jpl.nasa.gov/horizo ns.cgi)
> http://groups.google.com/group/lcross_observation/browse_thread/
> thread/0415e18d31ae7a04#
>
> Hope the above is helpful. It is intended to make - or stimulate
> discussion of - a rough estimate of the perimeters of the apparent
> brightness of the impact event for the purpose of making a rationale
> choice for settings for astrophotography of the event.
>
> Clear Skies - Kurt
>
> Addendum - Conversion of Spectral Radiance at 550nm to Visual
> Magnitudes
>
> str = steradians; m = meters; //* = note; sb = Stilb ; "Cox" refers to
> Allen's Astrophysical Quanitities at pp. 20-21
>
> 40 Watts (W) str^-1 m^-2 micron^-1
>
> 1 micron = 10^-6 m
>
> 40 W str^-1 m^-2 \ 10^-6 m
>
> 550 nanometers = 550 * 10^-9 = 0.55 * 10^-6 m
>
> [ 40 W str^-1 m^-2 \ 10^-6 m ] * 0.55 * 10^-6m = 22 W str^-1 m^-2
> //* (Spectral radiance with normalization backed out)
>
> 1 lumen at 550 nanometers = 1.470 * 10^-3 W = 680 lumens per W
> //* Cox
>
> 22 W str^-1 m^-2 [ 680 lumens / W ] = 14960 lumens str^-1 m^-2 = 1.496
> * 10^4 lumens str^-1 m^-2
>
> m^-2 = 10^4 cm
>
> 1.496 * 10^4 lumens str^-1 m^-2 [ 10^4 cm / m^-2] = 1.496 * 10^8
> lumens str^-1 cm^-2
>
> 1 sb = 1 lumens str^-1 cm^-2 //* (Cox)
>
> 1.496 * 10^8 lumens str^-1 cm^-2 = 1.496 * 10^8 sb
>
> 1 nit = 1 candela m^-2 = 1 cd cm^-2 = 10^-4 sb //* (Cox)
>
> 1.496 * 10^8 sb [ nits / 10^4 sb ] = 1.496 * 10^4 nits
>
> //* A separate spreadsheet at the following url covers the process of
> converting candelas per square meter ( cd/m^-2) or "nits" into visual
> magnitudes per square arcsec (MPSAS), based on R. Clark's 1990 _Visual
> Astronomy of the Deep Sky_:
>
> http://members.csolutions.net/fisherka/astronote/astromath/
> 20080215Unitsconversion.xls
>
> //* Details of the conversion between nits and MPSAS is not included
> here due to length considerations.
>
> 1.496 * 10^4 nits ~= 2.2 MPSAS outside atmosphere
>
> Say 2.4 MPSAS through one unit airmass
>
> For 10 W str^-1 m^-2 micron^-1, the conversion result is 3.7 MPSAS
> outside the atmosphere; say 3.9 MPSAS through one unit airmass
> extinction.
>
> For 1 W str^-1 m^-2 micron^-1, the conversion result is 6.2 MPSAS
> outside the atmosphere
>
>
> >

[cano...@yahoo.com]

Clif thanks for the comments. I decided to pull the post and deleted
it because I was not sure it was right. I'm following up more on the
question. Essentially it boils down to whether that 40 W str^-1 m^-2
micron^-1 covers an entire steridian or whether the radiance that your
telescope receives is just the small porportional part of a steridian
that an individual aperature or detector would receive. Realizing my
potential logic error, I deleted the top post. If it is the former,
then it would be the Mars-Saturn type event that I described in the
deleted post. If it is latter, then it will probably be a mag 15 or
16 event. Obviously, that effects how me and other amateurs are going
to approach imaging the impact event or whether they will attempt
imaging at all. (Some clubs have 1 meter scopes.) I'm trying to
track down some physics contacts to get the matter resolved so only
good information is posted here. My apologies for hitting the
posting button too soon.

I like your setup ideas. - Kurt

[Arnold Ashcraft]

Kurt:
I am sure that the 40 W str^-1 m^-2 figure is meant to cover a full
steradian and must be scaled to the area of a pixel of your camera using
the focal length of the telescope. The per meter squared unit is taken
care of by the aperture of your objective. That gets you directly to
watts
per pixel after you cancel out the units.
Clif

[cano...@yahoo.com]

Clif, How about a sample calculation? - Kurt

On Dec 13, 4:54 pm, Arnold Ashcraft <wa2...@optonline.net> wrote:
> Kurt:

[Arnold Ashcraft]

Kurt:
Like so...
Irradiance = 40 W per micron per square meter per steradian.

First, figure out the area of the curve given in the talk. Note that
the units of the vertical axis are the ones given above, and the
units of the horizontal axis are microns. The integral of that
function (the area) has units of W per square meter per steradian. I
integrated it approximately by dividing it into triangles and adding
them up. I got an area of 9.7 Watts per square meter per steradian.

Next, I multiply by area of my objective in square meters. My
Schupmann objective has a diameter of 7.25" which is 0.0266 square
meters. Multiplying 0.0266 by 9.7 gives me 0.258 watts per steradian.

Now we need to see what area of sky is projected on a single pixel of
my CCD. The pixels are 4.65 microns square. That works out to be
0.00000465 meters. My focal length is 232 inches when I am working
at f/32. That is 5.8929 meters. A pixel subtends an angle in
radians of 0.00000465 divided by 5.8929. That works out to be 7.9
times ten to the minus seventh (7.9e-07) radians. Well, the pixels
are square, so the area is just that squared, or 6.2e-13 steradians
per pixel.

OK, now we multiply the 0.258 watts per steradian by 6.2e-13
steradians to give 1.61e-13 watts per pixel.

That was where I got stuck until I remembered that a watt was a joule
per second and that I could calculate the energy of a photon in
joules using Planck's constant and the frequency of the light. Well,
to do it right, I should go back and fudge that irradiance curve to
account for the fact that photons have different energies across the
spectrum, but neglecting that for a while, and taking an average sort
of green photon at 6.0e+14 Hz and Planck's constant as 6.626e-34
joule sec, I calculate that a middle of the road photon is worth
about 3.976e-19 joules. That lets me turn the 1.61e-13 watts per
pixel into 4.05e+05 photons per second.

Let's now assume the quantum efficiency is about 50%. This gives us
2.02e+05 electrons per second accumulating in the well behind the pixel.

The well of my webcam CCD holds about 12000 electrons when full to
overflowing. It would take only 0.059 sec exposure to fill the well,
and at a typical exposure of 1/137th of a second that I used for one
of the pictures I uploaded to the files section, I would accumulate
1477 electrons. Not full by any means, but way over the noise floor
of 25 electrons or so for this chip. I am guessing this gives me a s/
n of 59, plenty enough to see it against a black background.

See attached Excel spreadsheet for the details.

Clif

[cano...@yahoo.com]

Thanks Clif. Wonderfully written. It'll take a while for me to
digest it. Clear Skies - Kurt

On Dec 16, 6:39 pm, Arnold Ashcraft <wa2...@optonline.net> wrote:
> Kurt:
>         Like so...
> Irradiance = 40 W per micron per square meter per steradian.

<snip>

[Arnold Ashcraft]

Kurt:
Meanwhile, I think I will go back to the beginning of the
calculation and do the conversions of watts to photons per sec to
electrons per second so that I account for the different energies and
quantum efficiencies across the spectrum, integrate the curve, then
put in the telescope aperture and pixel math. I don't think it will
make a big difference in the final result, but should be more rigorous.
Clif

[cano...@yahoo.com]

Thank you again, Clif. I was always wondering how radiance was used
to trace a target's light back into the detector and make an initial
estimate of the initial exposure time on a CCD. Your explanation is
very clear. It helped alot.

I do have one question regarding converting radiance into irradiance
by first dividing by your apeture size. How does your procedure
compensate for the different sizes of targets relative to the size of
your detector area? E.g. - the difference between imaging let's say
M101 so that it covers your entire detector vs. imaging a wide field
view of the Markovian chain where you might be concerned with the
radiance of one small galaxy within the entire detector's AFOV.

After you find the integrated radiance - 9.7 W str^-1 m^-2 instead of
dividing by the apeture of your detector, I was thinking in terms of
dividing by the target's size in steradians. That leaves an
irradiance value with the units of W m^-2. Then divide by your light
grasp - or sq meters of apeture. Then work back to the number of
Watts per pixel.

I'm asking this in the form of the question. Is there a more usual
procedure?

- Thanks, Kurt

On Dec 16, 6:39 pm, Arnold Ashcraft <wa2...@optonline.net> wrote:
> Kurt:
>         Like so...
> Irradiance = 40 W per micron per square meter per steradian.
>
> First, figure out the area of the curve given in the talk.  Note that  
> the units of the vertical axis are the ones given above, and the  
> units of the horizontal axis are microns.  The integral of that  
> function (the area) has units of W per square meter per steradian.  I  
> integrated it approximately by dividing it into triangles and adding  
> them up.  I got an area of 9.7 Watts per square meter per steradian.
>
> Next, I multiply by area of my objective in square meters.  My  
> Schupmann objective has a diameter of 7.25" which is 0.0266 square  
> meters.  Multiplying 0.0266 by 9.7 gives me 0.258 watts per steradian.

<snip>

[cano...@yahoo.com]

On Dec 17, 11:56 am, Arnold Ashcraft <wa2...@optonline.net> wrote:
> Kurt: Meanwhile, I think I will go back to the beginning of the  

> calculation <snip> - Clif

Clif - Here is what I came up with. I now have enough of a comfort
level that this thing probably can be seen and imaged. - Clear Skies,
Kurt

=======

For amateur visual and photographic observing, a crude first order
estimate of the visual magnitude of the ejecta curtain generated
during the first 60 seconds after the LCROSS EDUS impact is 1.6
integrated mags based on an assumed simplified ejecta curtain shape of
20x20 sq km subtending 11x11 arcsecs at the mean lunar distance of
384400 km. This estimate is based on limited publically available
data generated by the LCROSS Team. Uncertainty in this amateur
computation is large - curtain brightness could range between 0.8 to
5.0 mags and still be visually detectable. The purpose of making this
estimate was to quantify and test the NASA LCROSS warrant that the
ejecta curtain would be visible in 254mm or larger amateur class
apetures. "Mission scientists estimate that the Centaur impact plume
may be visible through amateur-class telescopes with apertures as
small as 10 to 12 inches." << http://lcross.arc.nasa.gov/observation.htm
(accessed 12/16/2008)>>. This note is intended to provide a "yes/no"
answer to that question and is not intended to be a precise modeling
of the visual magnitude of the ejecta curtain's magnitude.

Finally, I am novice at these types of astrophysics computations. As
individual amateur observers, consider the source and decide what
level of weight you feel the estimate should be given.

Even if the key parameter on which this estimate is based - the
fraction of solar irradiance emitted by the ejecta cloud towards Earth
- is off by a factor of 10, the ejecta cloud still will have an
integrated magnitude of about 5 mags. That is sufficiently bright to
have a detectable contrast against a bright moon-washed sky with a
worst case sky brightness of 15 mpsas.

At 1.6 magnitudes, the ejecta curtain will have a magnitude per square
arcsecs (mpsas) of about 6.8. This is fainter than the 5.3 magnitude
brightness of objects on a first quarter terminator, but much brighter
than a worst case sky brightness of 15 mpsas for the background sky
above the polar lunar limb. So, the ejecta curtain will not be
visible as it passes in front of the illuminated upper rim of a crater
like Faustini. To the extent that the ejecta curtain extends above
the rim of a polar crater like Faustini into the background night sky,
at 6.8 mpsas, the ejecta curtain will have sufficient contrast against
the background night sky to be detectable.

With respect to imaging, Saturn with a 6.7 mpsas is a good analogy for
starting camera settings. Saturn has been imaged egressing against
the bright limb of the Moon. E.g. - http://www.space.com/spacewatch/occult_pics_020221.html
. For imaging settings and practice, Saturn, which is visible in
December 2008 high in the sky in the early morning hours can be test
imaged. Then using those settings, image the terminator of the Moon
at the north and south poles during between the waning crescent and
first quarter phases. This is will provide some feel for how
capturing the LCROSS ejecta curtain will overexpose the Moon's bright
limb. As with photographing to dissimilar planets - such as Venus and
Mercury - it may be necessary to take two exposures. Make one
exposure to capture the ejecta cloud, a second to capture the lunar
limb. Then use digital image processing software to paste the ejecta
curtain exposure into the normal lunar limb exposure.

For me, there was a disconnect between published LCROSS presentations
and the potential amateur visual imaging experience. LCROSS websites
and published presentations from the prespective of professional
astronomers talk into terms of fantastically small levels of Watts
being generated by the event that require multiple meter telescopes to
capture while at the same time, amateurs can supposedly visually see
the impact. That disparity can be resolved by understanding that the
LCROSS earth-based spectrograph experiements are looking at a small
changes in micron swaths of a spectrograph in the infrared region.
The energy levels on the Earth that are trying to see are many times
less than the entire full spectrum of light that amateurs capture for
the purposes of imaging. Thus, it is entirely possible that a 10" or
12" with an imaging camera can capture a small faint fuzzy image of
the impact while at the same time not being able to image some
miniscule isolated frequency in the infrared that requires a multi-
meter apeture.

A previous post, based on the December 2008 LCROSS imaging campaign
session and Clif Ashcraft's image ( 20081208 0130ut
CASHCRAFT_200812080130.jpg in the files section ), concluded that the
LCROSS impact plume, if it rises to about 20km, should be sufficiently
large to be seen by amateur telescopes. This note concerns whether
the Sun reflected off the ejecta curtain will be sufficiently bright
to be detected visually.

This estimate was prepared without the benefit of information about
the internal LCROSS team current best estiamte impact model (CBEIM),
in particular the integrated power show for the spectral radiance
curve in Slide 24 of the May 2007 LCROSS AAS Presentation. url:
http://lcross.arc.nasa.gov/docs/LCROSS.AAS.ppt . A synthetic estimate
had be substituted for that data. This use of a synthetic estimate
adds to the uncertainty of the magnitude estimate presented here.

The method used to make the estimate of an integrated visual magnitude
relied on the differences of magnitude rule. Under the differences in
magnitude rule, where the visual magnitude and corresponding
irradiance of an object is known and the irradiance the second object
is known, then the magnitude of the second object can be found.
Algebraically, the differences of magnitude rule is:

m1 - m2 = 2.5 log10(I1/I2)
m2 = m1 + 2.5 log10(I1/I2)

where:

m1 = visual or photometric magnitude of the first object
m1 = visual or photometric magnitude of the second object
I1 = irradiance of the first object
I2 = irradiance of the second object

In this case m1 and I1 are:

m1 = -26.74 the visual magnitude of the Sun

I1 = 1370 W m^-2 the irradiance of the Sun's energy at a distance
from the Sun to just outside the Earth's atmosphere

I1 is also the irradiance of the Sun's energy at the north south poles
of the Moon - since the Moon is approximately the same distance from
the Sun as the Earth is.

I2 = W m^2 is the irradiance of the LCROSS ejecta curtain to just
outside the Earth's atmosphere

In the method used here, the irradiance of the Sun at the Earth's mean
distance (1370 W m^-2) is traced as it falls on the ejecta curtain.
The curtain reflects or re-emits a fraction this energy back towards
the Earth. The inverse square or luminosity distance law is applied
to the radiant flux of the ejecta curtain. This yields the irradiance
of the ejecta curtain (I2) just outside the Earth's atmosphere.

With m1, I1 and I2 being known, m2 can be calculated.

The luminosity distance law states that the irradiance (F) of an
object at distance (d) is:

F = L / ( 4 pi d^2 ) where:

L is the total Watts of energy emitted by the object

d is the distance from the object to observer in meters

An often used example of the luminosity distance law is the irradiance
of the Sun on the Earth:

L = 3.845 x 10^26 W - total radiant flux from the Sun
d = 1.5 x 10^11 m
F = 3.845 x 10^26 W / (4 pi (1.5 x 10^11 m )^2 ) = 3.845 x 10^26 W /
( 28.27 x 10^22 m^2)
= ( 3.845 W / 28.27 m^2 ) x 10^4 = 0.1360 x 10^4 = 1360 W m^-2

Names for units in these types of astrophysics problems were initially
confusing to me. Please see the following for further defintions of
terms and units used here.

http://en.wikipedia.org/wiki/Irradiance
http://en.wikipedia.org/wiki/Radiance

I have also prepared an Excel spreadsheet that contains the
computations discussed here and have placed it in the Files section of
this newsgroup. File: "20081216LCROSSCurtainMags.xls". A permalink
copy of that spreadsheet can be found at:

http://members.csolutions.net/fisherka/astronote/observed/LCROSS/20081216LCROSSCurtainMags.xls

References are made in this note to the corresponding worksheets in
that spreadsheet.

The Sun's irradiance at one Earth distance - the 1370 W m^-2 - is the
same on the Earth as at the poles of the Moon.

That solar irradiance will fall on the LCROSS impact ejecta curtain.
A certain fraction - unstated in the public LCROSS documentation -
will be reflected - that is it will have spectral emittance - back
towards the Earth. The whole Moon for example, has an albedo of about
12%. The full Moon reflects 12% of the solar irradiance back towards
the Earth.

Slide 24 in the May 2007 LCROSS AAS presentation <<
http://lcross.arc.nasa.gov/docs/LCROSS.AAS.ppt >> indicates that the
brightness of the impact ejecta curtain will hold for at least the
first 60 seconds. During that period, according to Slide 13 of
another LCROSS team member presentation << http://lunar.gsfc.nasa.gov/library/08_LCROSS_Bussey.pdf
>> the ejecta curtain may rise to as much as 20 kilometers.

Slide 24 in the May 2007 LCROSS AAS presentation of the sun's spectral
radiance essentially has the shape of the Sun's spectrum - the ejecta
curtain is just reflecting sunlight - but a much lower level than the
total 1360 W m^-2 full spectrum of irradiance reaching the curtain.

The difference between the full power irradiance of the Sun and the
lower reflected light levels in Slide 24 is due to many factors -
albedo of the ejected soil, particle size, particle density in the
curtain, angle of observed scattering, etc.

The usual process to estimate this loss would be integrate the total
power output of the full spectrum shown in Slide 24 and compare that
to to the full irradiance power of 1360 W m^-2.

The LCROSS team has not published that information and the low-
resolution figure in Slide 24 only allows a few crude chart take-
offs. There is no way to find the integrated power under the curve.

Nonetheless, a rough synthetic estimate of mean loss as the Sun's
irradiance that is reflected off the curtain can be made. That
estimate of loss can then be used to estimate the integrated power
under the curve in Slide 24.
Looking at Slide 24, I took off three points of spectral radiance
values:

500 nm - 38 W str^-1 m-^2 micron^-1
750 nm - 22.5 W str^-1 m-^2 micron^-1
1000 nm - 11 W str^-1 m-^2 micron^-1

Those values were converted into spectral emittance (W m-^2 micron^-1)
by multiplying by the spectral radiance by pi and compared at each
frequency to the spectral radiance of the Sun at one Earth distance
per Nickel and Lab (1984). << http://oceancolor.gsfc.nasa.gov/DOCS/RSR/Neckel_Labs_F0.dat
>>. Those computations are shown in worksheet "Radiative Transfer" in
file "20081216LCROSSCurtainMags.xls".

In summary, the percentage of the Sun's irradiance reflected back to
the Earth was estimated at:

500 nm | 6.2%
750 nm | 5.6%
1000 nm | 4.6%

As I was finishing writing this post, on Dec. 17 Clif Ashcraft posted
his chart take-off of the intergrated spectral radiance under the
curve shown on Slide 24 of the LCROSS May 2007 AAS presentation. He
estimated that the integrated spectral radiance at 9.7 W str^-1 m^-2.
Multiplying that value by pi yields the spectral emittance from the
curtain at 30.5 W m^-2 and implies a radiative transfer of 2.22% (1370
* 2.22% = 30.5 W m^-2). Clif's chart-take off estimate falls into the
sensitivity analysis range listed above. So, I added a 2.2% radiative
transfer scenario.

I adopted the 2.22% as a mean working value - recognizing that this is
not the scientifically correct way to estimate the radiative transfer
of the LCROSS ejecta curtain. Because this is a very crude way to
estimate the radiative transfer of the ejecta curtain, I also did
sensitivity analysis based on arbitrary radiative transfer percentages
of 1.00%,0.50%, 0.25%, 0.10% and 0.01%

assumed
radiative
transfer | sol irradiance | radiant emittance at curtain
6.2% | 1370 W^m | 84.9 W m^-2
5.6% | 1370 W^m | 76.7 W m^-2
4.6% | 1370 W^m | 63.2 W m^-2
2.2% | 1370 W^m | 30.5 W m^-2
1.0% | 1370 W^m | 13.7 W m^-2
0.5% | 1370 W^m | 6.9 W m^-2
0.25% | 1370 W^m | 3.4 W m^-2
0.1% | 1370 W^m | 1.4 W m^-2
0.01% | 1370 W^m | 0.1 W m^-2

For discussion purposes, a radiative transfer of 2.2% is used as the
working value.

If the solar irradiance falling on the current is 1370 W m^-2 and the
radiative transfer fraction is 2.2%, then the radiant emittance of the
curtain over the entire spectrum is estimated at 30.5 W m^-2.

If we assume a 20 x 20 km ejecta curtain then the total radiant flux
or Watts emitted by the curtain towards the Earth is 4.0 x 10^8 m^2
times 30.5 W m^-2 or 1.22 x 10^10 Watts.

The mean Earth-Moon distance is 384400 km ( 3.84 x 10^8 m ). Now
using the luminosity distance formula that was demonstrated above for
the Sun's irradiance, we can find the irradiance of the LCROSS ejecta
curtain just outside the atmosphere of the Earth:

L = 1.22 x 10^10 W - total radiant flux from the LCROSS ejecta
curtain
d = 3.84 x 10^8 m
F = L / ( 4 pi d^2 ) = 6.57 x 10^-9 W m^-2

These computations are shown in worksheet "Irradiance at Earth" in the
Excel spreadsheet "20081216LCROSSCurtainMags.xls".

Changing the radiative transfer percentage in cell C3 in worksheet
"Irradiance at Earth" automatically propogates throughout the
remainder of the computations in the spreadsheet.

This irradiance of the LCROSS ejecta curtain outside the Earth's
atmosphere (1.36 x 10^-8 W m^-2) is the value of I2 in the differences
of magnitude rule discussed above. I1 is the solar irradiance at one
Earth distance - 1370 W m^-2. 1370 W m^-2 corresponds to visual or
photometric magnitude -26.74.

The result of differences of magnitude rule computation for the above
values is an integrated magnitude of 1.56, rounded to 1.6 visual
magnitudes.

Those computations are shown in worksheet "Magnitude Difference Rule"
in file "20081216LCROSSCurtainMags.xls".

Sensitivity analysis at radiative transfer rates of 1.00%, 0.50%,
0.25%, 0.10% and 0.01% yields visual magnitude estimates of 2.43 at
1.0%, 3.18, 3.93, 4.93, and finally 7.43 at 0.01%. See worksheet
"Sensitivity Analysis" in file "20081216LCROSSCurtainMags.xls".

In conclusion, it would appear that the LCROSS ejecta curtain that is
20x20km and subtends about 11 arcsecs at the mean lunar distance is
bright enough to be seen in 10 and 12 inch class amateur telescopes.
Even if the crude estimate of the fraction of radiative transfer used
here is off by an order of magnitude, the ejecta curtain should still
be visible.

The ejecta curtain is an extended object. Therefore, like with other
extended objects like galaxies and nebula, it is useful to discuss
their brightness in terms of magnitudes per square arcsec against a
background brightness also expressed in mpsas. The supporting
computations of mpsas of the ejecta curtain and other lunar features
are in worksheets "ContrastIndex" and "SensitivityAnalysis" in file
"20081216LCROSSCurtainMags.xls". Discussion of the results is above
and is not repeated here.

Based on limited available information regarding predicted
characteristics of the LCROSS ejecta impact curtain, the curtain's
estimated 1.6 magnitude brightness appears too be bright enough and an
estimated 20x20km ejecta curtain is large enough to be seen visually
and imaged by amateur class gear. There is high level of uncertainty
to this crude calculation and a range possible of magnitudes presented
here is 0.8 mags to 5.0 mags. This crude estimate is sufficient to
corroborate - for amateur imaging planning purposes - the warrant made
in the LCROSS website that "the plume lume may be visible through
amateur-class telescopes with apertures as small as 10 to 12 inches."
Hopefully, after mission launch and as the impact nears, the NASA
professionals will publish a much more refined visual estimate for use
by amateurs.

Again, I am novice at these types of astrophysics computations. As
individual amateur observers, consider the source and decide what
level of weight you feel the estimate should be given.

Corrections and comments on the above are always welcomed and
appreciated.

- Kurt

P.S. - In addition to the opportunity of observing the impact ejecta
curtain, as of this date - 12/17/2008 - two other observing
opportunities have been mentioned.

OH+ molecular cloud - Publically available LCROSS documents indicate
that over the day following the impact, solar radiation may dissociate
any water in the ejecta plume into a 100 km tall OH+ molecular cloud.
This would be similar to the outer halo of a comet that often was
imaged by amateurs in late 2007 around Comet Holmes. I have seen no
estimates of the spectral emittance from this cloud or whether it
might be imaged by amateurs making, let's say a 5 or 10 minute
exposure. Unlike comets that are imaged against a dark sky
background, the hoped for LCROSS molecular will occur just above the
bright limb of the Moon. During the actual impact, North and South
America will be facing the Moon. This does not mean that there is not
a significant imaging opportunity for amateurs in the Far East and
Europe. The point of the mission is to detect water. Amateurs with
observing points other than North America are in the best position to
image this OH+ cloud and may want to develop or follow information on
that opportunity.

Booster during lunar transfer orbit - In a post in the Google LCROSS
observing group, LCROSS team public education member Brian Day also
mentioned that NASA was considering providing data on the position of
the Centaur booster for public pleasure viewing and imaging. The
LCROSS Team felt that the booster would be bright enough to be
detected by amateur telescopes during lunar transfer.

[Arnold Ashcraft]

Kurt:

it's all in the units.  The irradiance is given in units with meters squared in the denominator, so I have to multiply by the telescope aperture in square meters.  There is also a steradian in the denominator of the units.  Since I wanted only the energy going into one pixel, I needed the area of sky subtended by one pixel of my CCD given what the focal length of my telescope was.  You get that by dividing the width of a pixel by the focal length, and I needed the solid angle, so I squared it to get steradians and then multiplied by the result.  The net result of these two operations was canceling out the meters squared and the steradians from the units of the irradiance.  

I don't need to know how big the plume is or how much area it subtends on my CCD because it is an extended source and I am just looking at how much is falling on one pixel, which is all I needed to calculate the exposure needed.  Only if it were smaller than one pixel would I have to worry about things like what you are talking about.

I have no idea what the usual procedure is.  What I did was just to look at the units and start multiplying by things that have the units I want divided by the units I want to get rid of.  These conversion factors effectively have the value of unity as long as you carry the units along and do the math on them as well as the numbers.  For example, one inch == 2.54 centimeters.  So I can take either the quantity (1 in / 2.54 cm) or (2.54 cm / 1 in) and multiply anything I want by it without changing anything.  To convert 54 inches into centimeters, I just do the multiplication: 54 cm x (1 in / 2.54 cm).  The cm in numerator and denominator cancel out, leaving me with inches in the numerator.  Doing the arithmetic on the numbers is the easy part, giving me 21.26 inches.  If the units I don't want don't cancel out, I must have done it upside down.  That's all I did with the irradiance.  Just play with the factors until I get the units I want and the arithmetic follows along behind and gives me the answer I need.

Clif

[Arnold Ashcraft]

Kurt:
I went back and converted the irradiance curve given in the talk
from units of watt/micron/meter sq/str all the way to electrons/sec/
meter sq/str
by using both the Planck equation and the quantum efficiency of the
detector at different wavelengths. After numerical integration I got a
value of 6.4e+18 electrons/sec/meter sq/str to which I then applied
the telescope aperture, focal length and pixel area. I came up with
a result which says I need about twice the exposure that my earlier
calculation gave. This is understandable given the fact that quantum
efficiency is not 50% over the whole spectrum, which my earlier
calculation assumed. I have shortened my focal length a bit, down
to 210 inches. With the new focal length and new integration I now
expect that 1/137th of a second will give me a s/n ratio of 31. One
50th
of a second will give 65 and a 25th of a second will give 170. All of
these s/n ratios should result in a visible image of the plume.
So, I think we both are coming up with the same general conclusion,
ie, if we image the moon at our normal exposures for showing lunar
detail, we should image the impact plume as well.
Clif

[cano...@yahoo.com]

On Dec 17, 3:21 pm, Arnold Ashcraft <wa2...@optonline.net> wrote:
> Kurt: <snip> So, I think we both are coming up with the same

> general conclusion, ie, if we image the moon at our normal
> exposures for showing lunar detail, we should image the
> impact plume as well. Clif

Yes, it's not likely to be some kind of an odd mag 15 - 19 event. The
ejecta curtain is something that can be seen and photographed with 10
inch and above apetures. The problem with the event is that it is a
one-shot and maybe once-in-a-lifetime occurrence with alot of
uncertainty as to what the plume will look like. Considering those
constraints, if you are forced to guess at an exposure setting to
image a rare one-shot event, it is best to at least make an educated
guess as what those settings should be - using both visual magnitudes
and CCD exposure methods - as we have tried to do here. See you in
January. Clear Skies. - Kurt

[Arnold Ashcraft]

Kurt:
Note that my calculations were for a 7.25 inch aperture telescope.
I just plugged in a five inch aperture and found a very healthy 75:1
signal
to noise ratio for a frame exposure of 1/25th of a second. I would not
discourage anyone from trying this with a small telescope, and certainly
an aperture of 10 in and above will be plenty.
I have a 12.5" reflector too, but I will be trying to image the
ionized OH
cloud with my ST-8 and longer exposures. That cloud will be more
persistent
than the impact ejecta plume.
Clif

[cano...@yahoo.com]

On Dec 17, 1:09 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
<snip all>

Here's some followup on estimating the brightness of the LCROSS
impact. In this post, I give a low-bound estimate. The prior Dec. 17
post concerned a high-bound estimate. - Clear Skies - Kurt

=======

I. Search of S&T for historical reports

A historical search of Sky & Telescope issues around the time of lunar
impacts by Apollo LEMs and Saturn IV boosters was done. A NASA list
of LEM and Saturn IV-B impacts was used as a guide. NASA Impact List
(2008). Each S&T issue for three months following an event was
examined. Apollo preliminary science reports were reviewed. No
references to Earth-based observations of flashes or ejecta curtains
associated with any impact were found.

II. Low-bound ejecta current brightness estimate

In a prior note, I made a high-bound estimate of the apparent
brightness of the LCROSS ejecta curtain at 1.6 integrated mags based

on an assumed simplified ejecta curtain shape of 20x20 sq km

subtending 11x11 arcsecs at the mean lunar distance of 384400 km,

based on limited publically available data generated by the LCROSS

Team. Mention was made of low-bound prudent model for a 10km wide and
5km tall ejecta curtain used by the LCROSS Team.

This note provides more detail on this low-bound 10 x 5km ejecta
curtain model. My estimate of this low-bound 10 x 5 km ejecta curtain
subtending 5.5 by 2.75
arcsecs that obtains maximum brightenss between 40 and 60 seconds
after impact is 3.5 magnitudes - or 6.6 magnitudes per square arcsec
(mpsas).
In this low-bound estimate, the ejecta curtain will only peak above
the Faustini crater rim revealing only one or two arcsecs to Earth
based observers. The ejecta curtain would not rise to a height such
that it would contrast against the night sky or shadowed lunar limb.
If the opposite wall of the crater is illuminated relative to an Earth
observer, the ejecta curtain may not be observable against the
opposite crater wall's brightness.

In this low-bound scenario, amateur Earth-based imagers would see or
capture only a faint illuminated strip above the crater rim.

To understand the implications of the low-bound scenario, I recommend
close review of Clif Ashcraft's image of Faustini from the December
2008 LCROSS Observing Campaign. ( 20081208 0130ut
CASHCRAFT_200812080130.jpg in the files section in the LCROSS
Observing Campaign Google Group. http://groups.google.com/group/lcross_observation
) Note the subtle lighting of the partially illuminated southern rim
of Faustini with respect to the permanently shadowed northern side of
the crater.

Supporting computations for this low-bound estimate are in spreadsheet
"20081222LCROSSCurtainMagsKaf.xls".

http://members.csolutions.net/fisherka/astronote/observed/LCROSS/20081222LCROSSCurtainMagsKaf.xls

This revised low-bound estimate was developed based on a LCROSS Feb.
2008 astronomer workshop slideshow indicating that the irradiance at
Earth for the 10 x 5km ejecta curtain would be slightly more than
1*10^-9 W m^-2.

Using the spreadsheet model discussed in my first note, I developed
model for that irradiance using a 10 x 5km curtain and a 3% radiative
transfer. That curtain model yields an irradiance at Earth of 1.1 *
10^-9 W m^-2, or an equivalent 3.5 integrated magnitudes or 6.6
mpsas.

This estimate reenforces the prior recommendation of a suggested
starting camera exposure based on the settings for imaging Saturn - a
6.7 mpsas object - erroring on the fainter side and overexposing
Saturn.

IMHO, neither estimate should deter practiced imagers from attempting
to capture the ejecta curtain next August. The LCROSS impact is a one-
shot, rare event with uncertain characteristics that may not be
repeated for some decades. There is considerable uncertainty to the
LCROSS Team models. On the scale of the impact, lunar soils within a
particular crater are not well-characterized. The impact ejecta
curtain may be dimmer or much brighter than anticipated.

Hopefully, as the impact date next year approaches, the LCROSS team
will provide more backmatter detail on expected brightness of the
ejecta curtain for their website warrant that "Mission scientists

estimate that the Centaur impact plume may be visible through amateur-
class telescopes with apertures as small as 10 to 12 inches." <<
http://lcross.arc.nasa.gov/observation.htm (accessed 12/16/2008)>>.

III. Location of the LCROSS Sheparding Satellite Impact

After the 2000kg Centaur booster is impacted, one publically available
LCROSS document indicates that the 700kg sheparding satellite will
impact within 10km of the Centaur impact site about 10 minutes later.
This probably follows from the fact that the sheparding satellite will
basically fall behind the Centaur and trail it for imaging purposes.

IV. OH cloud not observable with amateur CCDs at 308nm

The OH- cloud will probably cannot be imaged using amateur grade CCD
cameras - but as discussed in later sections, there may be other vapor
cloud imaging options.

But LCROSS documents and Goldstein (2001) mentioned that an OH- cloud
is and will be brightest in the 308nm range. This is beyond the range
of a Bessell-Cousins U filter. See Optec Bessell filter response
curve charts at url: http://www.optecinc.com/pdf/bessell_25,4mm_transmission.pdf
(accessed Dec. 22, 2008). That frequency appears to be beyond the
spectral response curve of an amateur imaging camera like an SBIG10 -
which typically have an spectral response range between 350nm and
1100nm. See Tonkins, Amateur Spectroscopy. Some advanced spectroscopy
amateurs may have photomultiplier equipment that can reach the
required frequency.

Review of the unsuccessful Lunar Prospector journal literature also
may be informative. A bibliography is attached, but most of the
articles are only available via the internet by subscription service.
Reading the cited articles will require a trip to your local
university library.

I was not able to find much useful information in publically available
LCROSS team documents regarding the brightness of the OH plume beyond
a reference to a possible 100km cloud and references to the
unsuccessful attempt to image an 18 kg OH plume that was hoped to have
been produced from the 1999 impact of the Lunar Prospector into
Shoemaker. In contrast to the 18kg predicated for the Lunar
Prospector, the LCROSS Team planning assumption for OH production is
that a water content of 1% of 200,000 kg of ejecta material will raise
about 100kg water vapor and 1000kg of water ice over 35km above the
lunar surface.

See Slide 23 in the LCROSS May 2007 Presentation. url:
http://lcross.arc.nasa.gov/docs/LCROSS.AAS.ppt .

One counterintitutive characteristic of the OH cloud is its size.
Goldstein (1999) were thinking in terms of an eventual 1000 km radius
thin OH exo-lunar atmosphere forming from the Lunar Prospector impact
- all that with just 18kg source material. The 1999 attempt was
unsuccessful and probably inconclusive due to the difficulty of
detecting the faint signal from such a small amount of the material.
Goldstein et al (2001); Barker et al (1999). Pre-impact models did
not account for the unexpected effect of a lunar limb shadow
temperature sink. Cold temperatures on the Moon's shadowed surface
may have trapped a portion of the ejected vapor. Goldstein et al
(2001).

V. If the OH cloud cannot be observed, what about a hydrogren vapor
cloud in H-alpha and H-beta wavelengths?

One LCROSS Team presentation discusses the development of the OH cloud
after the impact by solar energy disassociating water and producing
ionized OH- molecules. After 25 minutes an OH molecule production
rate of 82,000 sec and a solar flux at 308 nm of 1 x 10^20 photons m-2
sec-1 mm-1 str-1.

As any basic chemistry course teaches, water is made of H2O and if
broken down into OH-, an ion of H+ necessarily also must be produced.
The Sun's radiation can then ionize this H+ into the familiar H-I and
H-II that is the bread and butter of amateur's H-alpha and H-beta
filters.

Even if the OH cloud cannot be imaged, an associated hydrogren cloud
may be created that can be imaging by amateurs.

Publically available LCROSS Team documents do not analyze the fate of
the H+ ion product of the H2O breakdown. Although the LCROSS
experiment is concerned with the level of possible hydrogren
enrichment of lunar soils near the poles, the detection of hydrogren
does not necessarily imply the presence of water.

The amateur community might give thought to the possibility that, if
water is contained in the ejecta cloud, an associated ionized
hydrogren cloud might be produced and be a target for amateur imaging.
As noted above, no analysis of this matter appears in the LCROSS Team
publically documents, so the starting point for further amateur
discussion would be physics of H molecular production, ionization and
likely emissions.

In an only tangentially related historical report, a Sky & Telescope
back issue from the Apollo era revealed an interesting amateur
observed event. __________. April 1971. Observer's Page: Some Optical
Observations of Apollo 14. Sky & Telescope 41(4):251-257. On Jan. 31,
1971, the Apollo 14 Saturn-IVB third stage dumped its excess hydrogren
load. Three hours later, the S-IVB dumped its excess liquid oxygen.
The fuel dumps were pre-announced by NASA and many amateurs attempted
to observe and image the event. John Bortle observed the hydrogren
dump as a 1 deg 1st magnitude object. Many amateur observers reported
the H cloud between 1 and 2 degrees in diameter and 0 to 1 magnitudes.
The volume of hydrogren dumped is not stated in the article but the
distance to the event is stated at 18,000 miles.

VI. Other miscellaneous elements, molecules and wavelengths

A) ionized H20+ at 619nm

Publically available LCROSS Team documents also indicate that visual
monitoring for H20+ is planned at 619nm. This is within the range of
amateur CCD cameras. There is no analysis of the likely brightness at
Earth of ionized water vapor. It's visibility in amateur equipment is
unclear.

B) ionized sodium vapor (Na) at 589nm

Publically available LCROSS Team documents do not analyze any
opportunity for enhanced sodium lines in the ejecta curtain. Since
elemental sodium emits at the same wave length as light polluting
sodium street lamps, the opportunity to observe any enhanced sodium
lines with amateur spectroscopy equipment is assumed to be small.

Apollo 14 lunar soils averaged 0.42% elemental sodium, principally in
the mineral Na2O that averaged 0.57% by weight. Apollo 14 Preliminary
Science Report at Table 5-IVI, p. 120. Apollo 16 highland rock
samples also average about 0.5% Na2O by weight. Apollo 16 Preliminary
Science Report at Table 7-III, p. 7-5.

Since the LCROSS impact is expected to excavate 200,000 kg of soil,
that volume of soil could contain 1000 kg of Na2O that includes 800kg
of elemental sodium. Publically available LCROSS team documents do
not analyze whether the impact or solar radiation on the ejecta
curtain will produce enough sodium vapor to emit a detectable signal.

The Moon has a thin exosphere that consists in part of vaporized
elemental sodium. The source of the sodium gas is the lunar regolith.
The gas is liberated by meteor impacts and solar radiation. New Views
of the Moon (2006) at 199-201.

In a 1998 serendipitous discovery, neutral sodium gas from was
observed at the antisolar point. The source of the sodium vapor was
the vaporization of lunar soils during the November 1998 Leonid meteor
bombardment. The excess vapor collected at the Moon's antisolar point
was observed by a simple amateur class all-sky camera: a Minolta 16mm
f/2.8 lens, a sodium narrowband filter, and a CCD camera. Smith et al
(1999); Wilson et al (1999).

Neutral sodium vapor strongly emits at 589nm.

Smith and Wilson were using the all-sky camera to conduct long-term
monitoring of how gravity waves effect sodium in the Earth's upper
atmosphere. The sodium vapor cloud concentration from the Moon was an
accidental capture on their nightly all-sky runs. Both Smith et al
(1999) and the related Oct. 1999 Sky & Telescope article both include
black & white images showing the sodium cloud.

Again, publically available LCROSS Team documents do not analyze the
potential for sodium vapor production from the impact. This may be
another area that expert amateur spectroscopers may want to consider
further.

VII. Imaging the Centaur during trans lunar orbit

LCROSS public education team member Day mentioned the team was
considering amateur imaging of the outbound Centaur stage.

Modern amateur Centaur booster imaging to 10,000 km and magnitude 6
have been reported on the SeeSat observing list. Hatton (undated).
url: http://www.satobs.org/centaur.html .

In Oct. 1997, amateur Gorden Garradd imaged the Centaur booster of the
outbound Cassini probe at 26,000 km using a 25cm f/4.1 Newtonian at 17
seconds exposure using hypered Kodak Gold III 400 ISO.

At 26,000km, geosynchronous satellites are an ordinary amateur
astrophotography challenge using 106mm of aperture. E.g.
Geosynchronous Satellites near the Orion Nebula. url:
http://www.mistisoftware.com/astronomy/FSQ106_GeoSynSat.htm .

A historical search of Sky & Telescope issues during the Apollo era
revealed amateur and professional observations of Apollo trans lunar
orbit insertions and the outgoing and returning Command Modules. The
"Moonwatch Division" of the Smithsonian Astrophysical Observatory
distributed distributed predicted locations of the outbound Apollo
Command Module and booster.
See Sky & Telescope 41(4):251-257 (April 1971), above. Observations
reported in the article included:

On Jan. 31, Fernbank Science Center imaged the Command Module and two
33 ft Saturn IV adapter panels at 18,000 miles (29,000km) using 36" of
apeture. A Center scientist also visually observered the Command
Module and the adapter panels in a 6 inch refractor finder scope as
mag 10 or 11 objects.

On Jan. 31, F.J. Eastman visually observed the 11 mag Command Module
in a 12 1/2 inch Newtonian.

On Feb. 1, 1971, the Fernbank Science Center imaged the Command Module
as a mag 13 object and the engine plume during a mid-course burn
correction using a 36" apeture. No distance is stated in the article,
but the Apollo 14 Mission Report at Table 6-III indicates that the
first mid-course correction burn occurred about 30 hours into the
flight and at about 118,000 miles (190,000km) from the Earth.

On Feb. 7, 1971, the Univ of Oregon, using a 24 inch apeture, imaged
the returning Command Module at 177,830 miles (286,000km).

On Feb. 8, 1971, the amateur observers were reported to have visually
seen the Command Module in an 8 inch reflector when the CM was about
106,000 miles (170,000km) from Earth.

Considering the current level of amateur practice in obtaining light
curves from mag 10 to 13 asteriods and modern reports of imaging
Centaur boosters to 26,000km, following a Centaur booster for a
considerable portion of its trans lunar orbit appears probable for 8
to 12 inch amateur class telescopes equipped with modern imaging
cameras. The potential for observing a hydrogren dump from the
booster is dependent on the launch time. If the launch occurs near
midday, a trans lunar hydrogren dump within 4 hours of launch during
the early trans lunar orbit would be obscured by the Sun. If the
launch occurs towards dusk or at night, imaging a fuel dump is
possible.

VIII. Practice imaging leading up to the event

A. Generally

Although it is unknown whether an hydrogen cloud will be visible at
the LCROSS impact (as a biproduct of the solar radition disassociation
of H2O into OH- and H+, an attempt at long-period exposures might be a
useful exercise. Between now and next August, I believe that the best
that amateurs can do is to use the favorable libration dates
identified in my prior post to practice long exposures (several
minutes) with the camera frame pointed just above the lunar limb at
Faustini or Byrd C-D and containing just one small bright feature at
the bottom of the frame for autoguiding purposes. H-a or H-b filters
might be employed.

Clear filter photometry studies at favorable librations would help
establish the magnitude of the background shadowed lunar limb and the
night sky just above the limb.

B. Lunar Occultations of the Pleiades

While leafing through historical Sky & Telescope issues from the
Apollo era, I ran across an article showing images of 4 magnitude
Pleiades star Merope grazing the south lunar pole. ________. Oct.
1969. August Occultations of the Pleiades. Sky & Telescope 38(4):
269-270. The south lunar mountains M1 and M5 are visible.

This suggested that imaging practice to determine camera settings to
capture 4th to 7th magnitude objects above the bright lunar limb
(analogous to the LCROSS ejecta curtain) might be done during 2009
lunar passages of the Pleiades. The RASC 2009 Observer's Handbook
lists the following lunar passes by the Pleiades and other bright
stars:

20080131 13UT Antares 0.02 deg S of Moon
20080204 03UT Moon 0.9 deg N of Pleiades
20080217 21UT Antares 0.04 deg S of Moon
20080303 08UT Moon 0.8 deg N of Pleiades
20080317 05UT Antares 0.2 deg S of Moon
20080330 14UT Moon 0.6 deg N of Pleiades
20080413 13UT Antares 0.4 deg S of Moon
20080426 21UT Moon 0.4 deg N of Pleiades
20080510 21UT Antares 0.5 deg S of Moon
20080615 23UT Juno 0.4 deg N of Moon, occultation North America
20080620 17UT Moon 0.5 deg N of Pleiades
20080704 10UT Antares 0.5 deg S of Moon
20080718 03UT Moon 0.5 deg N of Pleiades

City specific graze and occultations near the poles can be determined
using the Int'l. Occultation Timing Assoc. (IOTLA) city occultation
lists or by installing the IOTLA recommended graze software - Occult
v4.05.

Occult v.4
http://www.lunar-occultations.com/iota/occult4.htm

IOTA City graze list
http://www.lunar-occultations.com/bobgraze/index.html

Because of the LCROSS Team's uncertain designation of some slide
presentations for public release, some documents referenced above have
not been included in the attached bibliography.

I hope the above info are of help in your amateur LCROSS pre-planning
efforts leading up to August 2009. Corrections and criticisms to the
above are welcomed. My apologies for the overlength post.

Clear Skies - Kurt

Bibliography

A. LCROSS Team public documents and other journal articles

Bart, G.D., Colaprete, A. 2008. LCross Impact Site Charactertization.
NLSI Lunar Sci. Conf. url: http://www.lpi.usra.edu/meetings/nlsc2008/pdf/2037.pdf
(last accessed Dec. 22, 2008).

Bussey, B. April 27, 2008. The Lunar Polar Environment. (Slide
Presentation). url: http://www.spudislunarresources.com/moon101.htm
(last accessed Dec. 22, 2008).

Heldmann, J.L. May 30, 2007. Lunar Crater Observation and Sensing
Satellite (LCROSS) Mission: Opportunities for Observations of the
Impact Plumes from Ground-based and Space-based Telescopes. (Slide
presentation). Presentation to American Astronomical Society
,
Honolulu, HI
. url: http://lcross.arc.nasa.gov/docs/LCROSS.AAS.ppt (last accessed
Dec. 22, 2008).

Heldmann, J.L., Colaprete T., Wooden, D. et al. 2008. Lunar Crater
Observation and Sensing Satellite (LCROSS) Mission: Opportunities for
Observations of the Impact Plumes from Ground and Space-based
Telescopes. Lunar and Planetary Science Conf. 39:1482 (abs. no.).
url: http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1482.pdf (last
accessed Dec. 22, 2008).

Korycansky, D.G., Plesko, C.S., Asphaug, E. 2008. LCROSS Impact
Predictions. Lunar and Planetary Sci. Conf. 39:1963 (abs. no.) url:
http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1963.pdf (last accessed
Dec. 22, 2008).

Jutzi, M. and Benz, W. 2006. Simulations of the LCROSS Impacct using
Smooth Particles Hydrodynamics (SPH). Lunar and Planetary Sci.
Workshop on Lunar Crater Observing and Sensing Satellite (LCROSS) Site
Selection (2006), Abstract #9005
. url: http://www.lpi.usra.edu/meetings/lcross2006/pdf/9005.pdf (last
accessed Dec. 22, 2008).

LCROSS Team. Undated. Astronomer Justification document. (Draft Word
document) url: http://lcross.arc.nasa.gov/docs/LCROSS.Astronomer.Justification.v4.doc
(last accessed Dec. 22, 2008).

LCROSS Team. Undated. LCROSS: Overview for Ground-based Observatories.
(Slide Presentation). url: http://lcross.arc.nasa.gov/docs/LCROSS_OverviewforObs.ppt
(last accessed Dec. 22, 2008).

NASA-LCROSS Team. Sept. 2006. Methods of Water Ice and Water Vapor
Detection. (Web page). url: http://lcross.arc.nasa.gov/water.htm (last
accessed Dec. 22, 2008).

NASA-LCROSS Team. 2008. Imaging Specifications. (Web doc). url:
http://www.nasa.gov/mission_pages/LCROSS/news/image_specifications.html
(last accessed Dec. 22, 2008).

NASA-LCROSS Team. 2008. Strategy and Astronomer Observation Campaign.
(Web doc). url: http://lcross.arc.nasa.gov/observation.htm (last
accessed Dec. 22, 2008).

NASA-LCROSS Team. 2008. LCROSS: Opportunities for Observations from
Ground-based and Space-based Telescopes. (Flyer). url:
http://lcross.arc.nasa.gov/docs/LCROSS.ObservationCampaignFlier.May2007.pdf
(last accessed Dec. 22, 2008).

Schultz, P.H. 2006. Shooting the Moon: Constratins on LCROSS
Targeting. Lunar and Planetary Sci. Workshop on Lunar Crater Observing
and Sensing Satellite (LCROSS) Site Selection (2006), Abstract #9012
. url: http://www.lpi.usra.edu/meetings/lcross2006/pdf/9012.pdf (last
accessed Dec. 22, 2008).


B. Differential magnitude method for estimating visual magnitude of
ejecta curtain

(Russell's article discusses early measurements of irradiance from the
Sun and Vega to estimate the visual magnitude of the Sun using the
differential magnitude method. A variation of that method is used
above to make an amateur high-bound and low-bound estimate of the
visual magnitude of the LCROSS ejecta curtain).

Russell, H.N. 1916. The Stellar Magnitudes of the Sun, Moon and
Planets. Astrophys. J. 43:103-129. url: http://adsabs.harvard.edu/abs/1916ApJ....43..103R
(last accessed Dec. 22, 2008)

C. Lunar Prospector Articles

Goldstein, David B., Austin, J. V., and Barker, E.S. et al. Dec. 2001.
Short-time exosphere evolution following an impulsive vapor release on
the Moon. J. Geophysical Res. 106(E12):32841-32846. url:
http://adsabs.harvard.edu/abs/2001JGR...10632841G (last accessed Dec.
22, 2008).

Shim, Jeong-yeon. 2001. Temporal Evolution of the Lunar Exosphere.
(Master's Thesis). url: http://www.ae.utexas.edu/research/cfpl/topics/jshim/research.html
(last accessed Dec. 22, 2008). (See also directory
url: http://www.ae.utexas.edu/research/cfpl/topics/jshim/ and direct
link to thesis paper at url: http://www.ae.utexas.edu/research/cfpl/topics/jshim/JY_PAPER.pdf
) (last accessed Dec. 22, 2008).


Barker, E. S., Allende Prieto, C. and Farnham, T. L. et al. Dec. 1999.
Results of Observational Campaigns Carried Out During the Impact of
Lunar Prospector into a Permanently Shadowed Crater near the South
Pole of the Moon. American Astronomical Society, DPS Meeting #31.
Bulletin of the American Astronomical Society. 31:1583. url:
http://adsabs.harvard.edu/abs/1999DPS....31.5903B (last accessed Dec.
22, 2008).

Goldstein, D.B., Nerem, R.S. and Barker, E.S. et al. June 1999.
Impacting Lunar Prospector in a cold trap to detect water ice. J.
Geophysical Res. 106(E12):32841-32846. url: http://adsabs.harvard.edu/abs/1999GeoRL..26.1653G
(last accessed Dec. 22, 2008).

D. Leonid meteor lunar impacts and the sodium tail

____________. October 1999. The Moon's "Leonid" Tail. Sky &
Telescope. 98(4):21.

Jolliff, B.L. et al (eds). 2006. New Views of the Moon. Rev. in
Mineralogy & Geochemistry. Vol. 60.

NASA. 1971. Apollo 14 Preliminary Science Report. NASA SP-272. url:
http://www.hq.nasa.gov/alsj/alsj-psrs.html (last accessed Dec. 22,
2008).

NASA. 1972. Apollo 16 Preliminary Science Report. NASA SP-315. url:
http://www.hq.nasa.gov/alsj/alsj-psrs.html (last accessed Dec. 22,
2008).

Smith, S.M., Wilson, J.K., Baumgardner, J. and Mendillo, M. June 1999.
Discovery of the Distant Lunar Sodium Tail and its Enchancement
Following the Leonid Meteor Shower of 1998. Geophy. Res. Ltrs. 26(12):
1649-1652. url: http://sirius.bu.edu/aeronomy/1999GL900314.pdf (last
accessed Dec. 22, 2008).

Wilson, J.K., Smith, S.M., Baumgardner, J. and Mendillo, M. June
1999. Modeling an enchancement of the lunar sodium tail during the
Leonid meteor shower of 1998. Geophy. Res. Ltrs. 26(12):1645-1648.
url: http://sirius.bu.edu/aeronomy/1999GL900313.pdf (last accessed
Dec. 22, 2008).

E. Apollo era amateur imaging of Apollo during trans lunar orbit and
modern Centaur imaging

__________. April 1971. Observer's Page: Some Optical Observations of
Apollo 14. Sky & Telescope 41(4):251-257.

__________. Undated. Telescopic Satellite Observations. url:
http://www.satobs.org/telescope.html#centaur (last accessed Dec. 22,
2008) (1997 Gorden Garradd image of Centaur booster at 26,000km).

Hatten, Jason. Undated (circa 2002). Observing Centaur Rocket
Boosters. (Web doc.) url: http://www.satobs.org/centaur.html (last
accessed Dec. 22, 2008).

Misti Mtn. Obs. 2006. Geosynchronous Satellites near Orion Nebula.
(Web doc.) url: http://www.mistisoftware.com/astronomy/FSQ106_GeoSynSat.htm
(last accessed Dec. 22, 2008).

NASA. 2008. Impact Sites of Apollo LM Ascent and SIVB Stages. Web doc.
url: http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_impact.html
(last accessed Dec. 22, 2008).

F. Lunar occultation of the Pleiades

________. Oct. 1969. August Occultations of the Pleiades. Sky &
Telescope 38(4):269-270

Herald, David. 2008. Occult v.4
Homepage. url:
http://www.lunar-occultations.com/iota/occult4.htm (last accessed Dec.
22, 2008).

Int'l. Occultation Timing Assoc. (IOTA). 2008. Int'l IOTLA 2009 City
Graze List. url: http://www.lunar-occultations.com/bobgraze/index.html
(last accessed Dec. 22, 2008).

[cano...@yahoo.com]

On Dec 26, 9:55 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> On Dec 17, 1:09 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> <snip all>

P.S. - This a wrap slew of background reading cites on past amateur
and professional imaging of boosters in orbit, the Smart-1 impact
flash, analogous lunar meteor impact flashes, and the modeling of
hypervelocity impacts. This is my last background info gathering post
on this topic. Note the Smart-1 impact flash - out of probably several
hundred amateur imagers world-wide - was captured by one amateur -
Peter Lipscomb - with 8 inches of aperture. - Clear Skies and Happy
Imaging, Kurt:

E. Apollo era amateur imaging of Apollo during trans lunar orbit and
modern Centaur imaging

Birtt, R.R. Sept. 12, 2002. Earth's Newest Satellite Could Hit Moon
Next Year. Space.com Newswire. url: http://www.space.com/scienceastronomy/mystery_object_020912.html
(last accessed Dec. 27, 2008) (A Saturn V third stage, probably from
Apollo 12, was discovered by amateur Bill Yeung at mag 16.5 at Earth's
L1 LaGrange Point with 18 inch of aperture. It was designated minor
planet J002E3. [The target distance is not stated, but L1 and L2
points are approximately 1.5 million kilometers from Earth.]).

Birtt, R.R. Sept. 11, 2002. Newfound Object Orbiting Earth is Likely
Apollo Junk. Space.com Newswire. url: http://www.space.com/scienceastronomy/mystery_object_020911.html
http://www.space.com/scienceastronomy/mystery_object_020912.html (last
accessed Dec. 27, 2008) (same).

Jorgensen, K., Rivkin, A. and Binzel, R. et al. May 2003.
Observations of J002E3: Possible Discovery of an Apollo Rocket Body.
Bulletin of the American Astronomical Society 35:981.
url: http://adsabs.harvard.edu/abs/2003DPS....35.3602J (last accessed
Dec. 27, 2008).

Pulliam, Christine. Oct. 2007. Project Moonwatch. Sky & Telescope.
__:____. (Generally about the Smithsonian Astrophysical Observatory
(SAO) Moonwatch Program referred to in the Sky & Telescope 1971
article regarding Apollo 14).

G. Historical lunar impact flash and ejecta cloud observations

Astronomia Observacional's Net-REA, Lunar Section. 2006. Results of
the Smart-1 Observing Campaign. url:
http://slrea-smart1lunar-impact-project-ing.blogspot.com/2006/08/reports-of-observations-of-campaign.html
(last accessed Dec. 27, 2008) (Amateur observing campaign for SMART-1
impact were negative for impact flash and ejecta cloud detection. The
NASA Meteoriod Environment Office, using 254mm of aperature detected
the flash only, but not the ejecta cloud.).

Beatty, J.L. Sept. 7, 2006. SMART 1's Dramatic Finale. Sky and
Telescope News. url: http://skytonight.com/news/home/3858532.html
(last accessed Dec. 27, 2008) ("Peter Lipscomb of Santa Fe, New
Mexico, who used a Meade LX-90 Schmidt-Cassegrain telescope and
Philips ToUcam Pro webcam" captured the impact flash of Smart-1.).

Cooke, W. J., Suggs, R. M. and Suggs, R. J. et al. May 2007. Rate and
Distribution of Kilogram Lunar Impactors. Lunar and Planetary Science
Conf. 38th. 38:1338 (abs. no.) at p.1986 (last accessed Dec. 27, 2008)
(Using 10 inch and 14 inches of aperture and amateur class video
imaging equipment, in 107 hours of observing the lunar crescent at a
limiting magnitude of 9, the Meteoriod Environment Program saw
20 potential lunar impact flashes between mag 7 and 9.4.).

Edwards, D.L., Cooke, W., Moser, D.E. and Swift, W. June 2008.
Measurement of Ejecta from Normal Incident Hypervelocity Impact on
Lunar Regolith Simulant. Earth, Moon and Planets 102(1-4):549-553 url:
http://www.springerlink.com/content/b825m439t2594448/ (last accessed
Dec. 27, 2008).

Ernst, C.M. and Schultz, P.H. May 2008. Effects of View Orientation on
Impact Flash Observations: Implications for Lunar Impacts. Lunar and
Planetary Science XXXIX. 39:1391 (abs. no.), p.2291 url:
http://adsabs.harvard.edu/abs/2008LPI....39.2291E (last accessed Dec.
27, 2008) (In high-velocity gun experiments, at 1500 nanometers side
view (90 degs) photometry of glass-ball impacts are 9 times fainter
than impact viewed from an above perspective.)

Lipscomb, Peter. Sept. 4, 2006. Newsgroup Post titled "Re: Smart-1
Impact animated.gif" Cloudy Nights Solar System Imaging & Processing
Newsgroup Message Id 1131502. url:
http://www.cloudynights.com/ubbthreads/showflat.php?Cat=&Board=Imaging&Number=1230888
(last accessed Dec. 27, 2008) (Lipscomb image).

Marshall Space Flight Center, Meteoroid Environment Office. 2008.
Lunar Impact List. (Webdoc). url: http://www.nasa.gov/centers/marshall/news/lunar/index.html
and http://www.nasa.gov/centers/marshall/pdf/155422main_ALAMO_lunar_impact_observations152.pdf
(last accessed Dec. 27, 2008).

Marshall Space Flight Center, Meteoroid Environment Office. 2008.
Publications List. (Webdoc). url: http://www.nasa.gov/centers/marshall/news/lunar/publications.html
(last accessed Dec. 27, 2008).

Montañés-Rodríguez, P., Pallé, E., and Goode, P. R. Sept. 2007.
Measurements of the Surface Brightness of the Earthshine with
Applications to Calibrate Lunar Flashes. Astronomical J. 134(3):
1145-1149. url: http://adsabs.harvard.edu/abs/2007AJ....134.1145M
(last accessed Dec. 27, 2008) (Measuring lunar surface brightness for
calibration of impact flashes, the authors found the lunar surface
varied between 12 and 17 magnitudes per square arcsec with variations
of 0.25 mpsas per hour.).

Suggs, R.M., Cooke, W.J., and Suggs, R.J. et al. June 2008. The NASA
Lunar Impact Monitoring Program. url: http://adsabs.harvard.edu/abs/2008EM%26P..102..293S
(last accessed Dec. 27, 2008)

Swift, W., Suggs, R. and Cooke, B. June 2008. Algorithms for Lunar
Flash Video Search, Measurement, and Archiving. Earth, Moon and
Planets 102(1-4):299-303. url: http://adsabs.harvard.edu/abs/2008EM%26P..102..299S
(last accessed Dec. 27, 2008)

Veillet, C. 2006. Observation of the Impact of Smart-1. (Web doc).
url: http://www.cfht.hawaii.edu/News/Smart1/#Dust (last accessed Dec.
27, 2008) (Using a professional infra-red webcam with 10s exposure
time and an H2 narrow-band filter at 2122 nanometers with a 32
nanometers bandwidth with the Canada-France-Hawaii Telescope with 3.6
meters of aperture imaged both the impact flash and ejecta dust cloud
from the Smart-1 low-angle impact on the dark limb of the Moon.).

Veillet, C. and Foing, B. May 2007. SMART-1 Impact Observation at the
Canada-France-Hawaii Telescope. Lunar and Planetary Conf. 38th.
38:1338 (abs. no.) at p. 1520.
url: http://adsabs.harvard.edu/abs/2007LPI....38.1520V (last accessed
Dec. 27, 2008).

Wood, C. Sept. 28, 2006. Smart-1 Crater Not Observed. LPOD. url:
http://www.lpod.org/?m=20060928 (last accessed Dec. 27, 2008) (Smart-1
impact not observed by advanced amateur imager Paolo R. Lazzarotti).

Wood, C. Dec. 27, 2008. Public Communication. (On February 20, 1965,
professional astronomers Alika Herring and Chuck Wood attempted
unsuccessfully to observer the flash of the impact of Ranger 8 using
Kitt Peak's 84" of aperture).