Using photometry to find skybrightness above the LCROSS impact site and impact brightness
cano...@yahoo.com
estimate at 550nm of the impact ejecta curtain brightness of
approximately 3.0 mpsas during the first between 10 and 60 seconds
after impact. Heldman (2009). A version of Heldman (2009) is
reproduced as a low-resolution frame on the LCROSS Team Observation
Campaign webpage (2009). url: http://lcross.arc.nasa.gov/impact.htm .
For amateur CCD or video imaging purposes, this understates the likely
mpsas, since CCD cameras respond to the broad integrated wavelengths
between approximately 380nm and 1000nm. CCDs do not respond at a
single wavelength.
The LCROSS-EDUS impact will generate a dust ejecta curtain about 10 km
x 5 km high between 40 to 60 seconds after impact according to the
NASA-LCROSS Team conservative best estimate impact model (CBEIM). Bart
(2008) at slides 19-20; Wooden (2008) at slide 2. This current
conservative LCROSS CBEIM translates to a 3 arcsec x 2.5 arcsec ejecta
dust cloud at a mean lunar distance of 384,400km. A larger
hypothetical 20 x 20 km ejecta curtain converted to a circular shape
of equal 400 sq km area has a diameter of about 12 km. As seen from
Earth at a mean lunar distance of 384,400 km, the 20 x 20 km square
billboard would be 11 x 11 square arcsecs, or equivalent to a circle
with a diameter of 12 arcsecs.
At those ejecta curtain sizes and an irradiance at a single wavelength
of 550nm of 3.0 mpsas, the corresponding integrated magnitudes of the
curtain would be 1 integrated magnitudes for the 10km x 5km scenario
and -1.9 integrated magnitudes for a 20km x 20km, 12 arcsec diameter
scenario.
This apparent brightness (3.0 mpsas) provides a favorable contrast
index against typical Earthshine (dark limb) irradiance between 12 to
17 mpsas for the dark limb (mean value 15.44 mpsas) but not against
Moonshine (bright limb) at 4 to 6 mpsas.
The LCROSS ejecta curtain will present a uniquely difficult extended
object for amateurs to image. The impact is hoped to occur when a
permanently shadowed region (PSR) is on or near the bright limb
terminator with the crater surrounding the PSR being partially lit at
a very low sun angle. The dust ejecta curtain will rise into the
sunlight and reflect light back to Earth-based telescopes against the
background darkness of the night sky immediately adjacent to the dark
limb.
At the moment of projected impact, 2009-10-09 11:30UT, the Moon will
have the following geocentric empheris characteristics:
Phase angle 65.2984
Perscent illumination 71% illumination
Terminator colongitude 158
Lunar age 20.7 days
The average sky brightness under moonlight scattered illlumination
(expressed in mpsas) at various distances from the Moon was modelled
with precision by Krisciunas and Schaefer (1991) based on earlier
measurements by Krisciunas (1990) and an earlier rough model by Walker
(1987). See Krisciunas (1990) at Figure 8, reproducing the rough model
of Walker (1987).
The effect of moonlight is additive. Under the rough Walker model, the
full Moon adds about -1.9 mpsas to whatever your base sky brightness
is. At a lunar age of 20 days, about -1 mpsas is added. If you are
observing from a light-polluted 3 integrated magnitude urban sky
(equivalent to about 16.9 mpsas), the light from a 20 day old Moon
adds on average about -1 mpsas to your sky brightness. That is it
would reduce a 16.9 mpsas sky to a 15.9 mpsas sky - equivalent to
about 2.1 integrated magnitude sky. Conversely, if you travel to your
favorite 21 mpsas - 6.1 integrated magnitude rural dark sky site, the
same Moon reduces sky brightness to 20 mpsas or 5.5 integrated
magnitudes.
The effect of moonlight is dependent on the lunar phase and the
degrees of distance between the Moon and the observed target.
Krisciunas and Schaefer (1991) (at Table 2) give the following rough
delta mpsas (as measured through a Johnson V standard filter) for the
lunar phase angle and distance between the Moon and the observed
target. These results are for their improved model over the Walker
(1987) rough model:
Phase angle Angular distance Moon-target
05 30 60
30 -4.5 -2.9 -2.2
60 -3.7 -2.1 -1.5
90 -2.7 -1.4 -0.9
120 -1.6 -0.6 -0.3
The value in Krisciunas and Schaefer's table closest to LCROSS impact
circumstances is a phase angle of 60 and an angular distance of 5
degrees. They report a delta mpsas of -3.7 for those circumstances.
(Lunar phase angle is the number of degrees between the Sun, the Moon
and the observer. It varies between 0 and 180 degrees. It is the S-T-
O angle reported by the NASA/JPL Horizon's Ephemeris system. Phase
angles less than 90 degrees imply backscattering of light; phase
angles greater than 90 degrees imply forward scattered light.)
For an urban 16.9 mpsas (3.0 integrated magnitude) sky, 60 degree
phase angle moon light would increase sky brightness near the Moon by
-3.7 mpsas to about 13.2 mpsas - or -0.5 integrated magnitudes. At
the rural dark sky site with an excellent 21 mpsas - a 6.1 integrated
limiting magnitude - moonlight was reduce the limiting magnitude to
17.3 mpsas or a 3.3 integrated limiting magnitude.
Equating (roughly and perhaps inapproriately) the LCROSS team's single
550nm wavelength mpas of 3.0 to the LCROSS ejecta curtain to the full
Johnson V-band mpsas, indicates that the LCROSS ejecta curtaion might
have a positive contrast index even in an urban light polluted
environment:
Sky
brightness
5 degs from Moon Curtain MPSAS Contrast Index
Urban 13.2 3.0 4.1
Rural 17.3 3.0 5.7
Even though the LCROSS ejecta curtain will be seen rising against a
bright background sky, at an average curtain brightness of 3.0 mpsas,
it still may be visible or subject to imaging.
An obvious implication of the above is that travelling a dark sky site
may improve the contrast between the ejecta curtain. Dark skies - even
though they are washed out by moonlight - still relatively increase an
amateur's likelihood of visually detecting the impact curtain and of
imaging the curtain.
An extended object fainter than 3.0 mpsas - such as Saturn - has been
widely imaged as it was occulted by the Moon. Saturn has a computed
mpsas of 6.7 based on an diameter of 14 to 20 arcsecs and an
integrated magnitude ranging between 0.4 to 1.2 mags. But unlike
Saturn, the LCROSS ejecta curtain will be a low-density dispered dust
cloud.
In an abbreviated literature search, no articles were found concerning
the additive effect of moonlight between 0 degrees and 5 degrees from
the lunar limb.
Lunar amateurs and lunar occultation amatuers are familiar with this
effect of moonlight. Only the brightest stars can be seen next to the
bright limb of the full Moon. Magnitude 4 to 7 stars disappear within
an arcminute of the bright lunar limb.
Amateurs in the LCROSS Google observation group ( url:
http://groups.google.com/group/lcross_observation ) have been
attempting to gain some understanding of the brightness of the night
sky above and within a quarter-degree of the lunar limb by observing
grazes and imaging stars during lunar occulations of clusters.
Example images are:
Chris Kitting. Moon occulting Pleaides 2009-08-14 9;46UT
http://01227941410742638900-a-g.googlegroups.com/web/CKitting_20090814_0946Pleiades.jpg
http://tinyurl.com/oopegs
Image details: http://groups.google.com/group/lcross_observation/msg/80c0f58084faec69
In Kitting's image, magnitude 7 to 8 stars in Merope's Tail are co-
exposed close to an overexposed lunar terminator.
Derek C. Breit April 25, 2007 6.6 mag star graze on dark limb
http://www.poyntsource.com/tmp/April_25th_2007_Graze.mpg (24 mb mpg)
These experiments have had limited success, principally because the
few number of such occultation events and uncooperative weather limits
the ability to gather useful data using those techniques.
An alternative technique would be CCD photometry analysis. In this
technique, the south pole of the Moon is imaged at high focal ratios
(f/30 plus) at various exposure times from underexposure to high over-
exposure. The camera and scope are then retargeted without changing
focal length or exposure on an open cluster at a similar altitude as
the Moon. The V magnitudes of open clusters are well-known and plots
of clusters limited by a specific magnitude are easily made using the
Webda's online database. url: http://www.univie.ac.at/webda/
The open cluster provides reference stars to determine simple
transform coefficients for the CCD camera at a given exposure setting
through standard B and V or C and V filters. Modern imaging
processing packages like AIP4WIN include photometry utilities by which
the differential magnitude of stars can be found and correlated to CCD
well ADUs. See single star photometry in Exercise C.5 in the AIP4WIN
handbook and the extractive photometry utility on the AIP4WIN menu
(Measure | Photometry| Extractive Photometry). The open cluster image
also provides an image scale that can be applied to your image of the
south pole.
This poster unsuccessfully attempted a preliminary test during the
August 14, 2009 lunar occultation of Pleaides. An image of the south
pole was taken, followed by an image of the Alcyone triple.
Unfortunately, weather conditions and an unanticipated glare problem
unquie to the Mak imaging scope prevented getting a useable result.
The Meade ETX 125 Mak has a curved corrector plate. When slewing from
the south pole to Alcyone, the Mak's curved surface diverted off-axis
lunar glare into the tube and washed out the image. No useable
photometry information could be gleaned from the image, but a
demonstration information on image scale could be found.
A panel summarizing this technique demonstration test can be seen at:
http://members.csolutions.net/fisherka/astronote/observed/LCROSS/2009_8_14_0246UT_KafTestPanel.jpg
http://tinyurl.com/n4l8sn
The next best - and last - analogous lunar south pole illumination to
the LCROSS impact will occur on September 9 11:30UT:
Lunar libration data for images and impact
Source: LTVT ephemeris data, topocentric W111.8 N41.8
Date-TimeUT libr_lat lib_long colong illumfrac
20090907 1130 -6.2 -5.5 128 92
20090908 1130 -6.2 -5.5 140.2 85.5
20090909 1130 -6.1 -5.4 152.3 77.3
20091009 1130 -3.5 2.8 158.2 70.9 Impact day
20090910 1130 -5.4 -5.1 164.4 67.7
20090911 1130 -4.4 -4.3 176.5 57.1
20090912 1130 -3.2 -3.3 188.7 45.8
Date-TimeUT Lunar age (days)
20090907 1130 18.1
20090908 1130 19.1
20090909 1130 20.1
20091009 1130 20.6 Impact day
20090910 1130 21.1
20090911 1130 22.1
20090912 1130 23.1
On the early morning of Sept. 8, there are no appropriate open
clusters near the Moon. NGC752 (Caldwell 28) is higher in the sky.
The Double Cluster is also at a higher altitude, but visible.
On the early morning of Sept. 9, the Moon and M45 will both be
visible, but the Pleaides will be a higher altitude.
On the morning of Sept. 10, the Moon will be near the Pleaides and at
the same altitude. On the evening of the 11th, a number of open
clusters might be used for baseline photometry - M45, M36, M37, M38 or
NGC1647.
As we approach full Moon on September 4, the Moon will be 68%
illuminated on August 29 (from the opposite direction). The night of
August 29 provides an opportunity to set up and test equipment under
test analogous illumination before September 9.
On the evening of August 29, the Moon will be low in the southern sky
just below the apex of the Sag "teapot". Open clusters M21, M23 and
M25 are also visible, but at higher altitudes.
Amateur photometry to determine sky brightness within one quarter
degree "above" the lunar south pole on September 8 through 11
(particularly on September 9) will help determine if the LCROSS impact
ejecta cloud will have sufficient contrast against the moonlight night
sky to be seen and imaged. Imaging through filter combinations (V-C,
V-I, B-V) will give the most accurate results. To confirm whether the
background sky brightness will not overwhelm the ejecta curtain
brightness, better photometry data might be collected by amateurs
within zero to 5 arcminutes "above" the south lunar pole.
Clear Skies - Kurt
Disclaimer: This is an amateur note. Criticisms and corrections to the
above are welcomed.
Fisher, Kurt A. (amateur). 2008. Conversion Calculator for NELM(V)
to MPSAS (B) systems. (Web calculator). url:
http://members.csolutions.net/fisherka/astronote/plan/tlmnelm/html/NELM2BCalc.html
(last accessed 26 Aug. 2009)
Heldman, J. (LCROSS Team). Email Feb. 11, 2009, Slide 4
(slide4.gif).
Krisciunas, K. 1990. Further measurements of extinction and sky
brightness on the island of Hawaii. PASP 102:1052-1063. Bib. Code
1990PASP..102.1052K url: http://adsabs.harvard.edu/abs/1990PASP..102.1052K
(last accessed 26 Aug. 2009)
Krisciunas, K. and Schaefer, B.E. 1991. A model of the brightness of
moonlight. PASP 103:1033-1039, Bib. Code. 1991PASP..103.1033K url:
http://adsabs.harvard.edu/abs/1991PASP..103.1033K (last accessed 26
Aug. 2009)
LCROSS Team. 2009. Average and Edge Brightness of Ejecta Curtain
(Figure). LCROSS Observation Campaign website. url:
http://lcross.arc.nasa.gov/impact.htm and http://lcross.arc.nasa.gov/observation.htm
Image: observation05.jpg (last accessed 26 Aug. 2009)
Walker, A. 1987. ________________. NOMO Newsletter. 10:16.
Derek C Breit
KURT WROTE-
This poster unsuccessfully attempted a preliminary test during the August
14, 2009 lunar occultation of Pleaides. An image of the south pole was
taken, followed by an image of the Alcyone triple. Unfortunately, weather
conditions and an unanticipated glare problem unquie to the Mak imaging
scope prevented getting a useable result. The Meade ETX 125 Mak has a curved
corrector plate. When slewing from the south pole to Alcyone, the Mak's
curved surface diverted off-axis lunar glare into the tube and washed out
the image. No useable photometry information could be gleaned from the
image, but a demonstration information on image scale could be found.
------------------------------------------------------
EXCELLENT !!!
This too is part of the reason to test.. Off axis glare is THE problem with
grazes or this type of event.
Flocking the nosepiece of the camera works very well to help eliminate SOME
of this glare, especially when it is (2) inch and a quarter discs of
flocking material placed two different distances from the detector, each
having holes of appropriate sizes of the on axis focal plane, i.e. the hole
is larger in the disc farthest from the detector.
Any scope that allows access to the inside of the OTA should already be
flocked, since it is simple to do and can yield a large increase in
contrast. This was a huge improvement on my 12" LX200, gaining me around a
full magnitude with a PC164 depending on conditions.
KURT ALSO WROTE, and I am paraphrasing, numbers about the ejecta curtain
expressed in km.. These numbers are reason to smile, as I have been hoping
to hear anything 8km or more. If these predictions are accurate and/or the
ejecta curtain happens to be brighter and a distance of 8km or more happens,
this will be vastly easier than anything I have heard previously. Comparing
this (which I barely comprehend and have been looking for the previously
mentioned keywords) to a mag 7 star grazing the south pole is exactly why I
am here.. I can do that. I did a graze 7 hours after a full moon and this
should be easier, so I am all jazzed about this again..
YEAH!
Derek
PS.. I live in mag six skies in Morgan Hill, CA. Any imager who lives near
here is more than welcome to accompany me in my Front Yard..
cano...@yahoo.com
<snip all>
Thanks, Derek. I believe you meant "magnitude" where you wrote "km"
for kilometer in your post. Here's another successful test mentioned
in a Cloudy Nights forum using a consumer camera:
Cloudy Nights Thread 3-10-20089 Moon Eclipsing 3 Stars of Seven
Sisters (M45)
Timo Keski-Petäjä
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2247501/
Using a 6Mb-pixel consumer grade Sony DSC-W50 camera, afocal with a
digital compact camera adapter, a C8 newtonian, and a built-in
exposure processing setting called "Beach", Timo was able to image
Pleaidean stars Electra (3.7 integrated mags) and Taygeta (4.3
integrated mags) occulting against the bright limb of the full Moon.
http://www.youtube.com/watch?v=eeXvZ7Ymrvg
"Beach" is simply an automatic exposure setting option within the Sony
DSC-W50.
http://www.dcresource.com/reviews/sony/dsc_w50-review/
One review describes the "beach" automatic processing mode as "Beach
limits the flash modes to Forced On or Forced Off, and shutter speeds
to a range that is faster than 1/8 second. Sensitivities can range
from 80 to 320 ISO and the camera increases blue saturation
slightly."
http://articles.directorym.net/Sony_DSC_W50-a941174.html
The Sony manual describes "beach" mode for use in shooting brightly
lit "Shoot waterside scene with rich blue color."
http://www.docs.sony.com/release/DSCW30-W40-W50-W70_rtf.pdf
Timo noted that he pointed the center of the camera image on the black
sky and not on the lunar disk. That way, the camera was making its
automatic exposure adjustments based on the darker sky and not on the
lunar disk.
What the "Beach" processing option does is unknown but illustrates
that some digital processing option exists which can render down to
mag 4.3 at the bright limb even at full Moon.
There is still considerable uncertainty concern the size of the
curtain and its brightness. So, don't do your happy just dance yet. I
suspect the waffling in LCROSS p.r. statements on whether the curtain
will or will not be visible is related to this inherent modelling
uncertainty. If the curtain will only be a one or two arcsec tall
line shape right on the bright limb - may still not be anything worth
looking at. I'm just keeping an open mind on the thing and what
happens, happens.
In the meantime I am just enjoying imaging the south pole for the
inherent worth and enjoyment of the hobby activity.
- Clear Skies, Kurt
cano...@yahoo.com
<snip all>
On the question of the faintest star visible before occultation on the
bright limb, it appears that Dr. Schaefer did an popular article on
this in S&T in 1993, summarizing his 1991 article. It was also turned
into one of the S&T BASIC programs available via the internet.
Schaefer, B. E. A star's visibility just before occultation. Sky
Telesc., Vol. 85, No. 1, p. 89 - 91 (S&T Homepage) Bib. Code
1993S&T....85...89S
url: http://adsabs.harvard.edu/abs/1993S%26T....85...89S
S&T DOS Program from 1993
http://media.skyandtelescope.com/binary/occvis.bas
in
http://www.skyandtelescope.com/resources/software/3304911.html
How to run a DOS QBasic program on a Windows XP Computer
http://www.skyandtelescope.com/community/hobbyqanda/3399826.html
- Clear Skies - Kurt
Derek C Breit
Thanks, Derek. I believe you meant "magnitude" where you wrote "km" for
kilometer in your post.
-----------------------------------------------
I don't know exactly what I wrote, but I doubt I meant magnitude.. 8 to 10
km is in the range of 2 arcseconds..
2 arcseconds from small amounts of bright limb and a mag 7 or 8 star (point
source) is rather easily seen.
This is what I was thinking..
But you know what I did actually write, so I will assume you are correct. I
type with two fingers and it would NOT be the first time my fingers did
their own thing while I was thinking something else..
As for Pleiades on the bright limb, wont touch that one..
Derek
cano...@yahoo.com
Jim Mosher
There is indeed an article called "A Star's Visibility Just Before
Occultation" in the January, 1993 issue of /Sky and Telescope/ (pp.
89-91) describing the computer program you mention. The program is
meant to be used to assist visual observations (as opposed to
photographic ones), and using 16 variables (including such things as
the observer's age and experience) claims to be able to calculate
either the maximum magnitude (dimmest) star that can be timed crossing
the limb with a given aperture telescope, or, alternatively, the
minimum aperture required to see the occultation of a star of a given
magnitude.
Since it appeared two years after the PASP article you referred to,
the program presumably implements Dr. Schaefer's numeric model of the
brightness of the moonlit sky (over Mauna Kea, Hawaii) plus his
notions about visual observing of stars. However since you found the
earlier article seemed to mention nothing about sky brightness closer
than 5° to the Moon he may be making some new assumptions about
that.
The difference between clear and hazy skies (which I would think would
be a major factor) appears to be determined by something called the
"visual extinction coefficient" ("K"). He says this ranges over the
surprisingly limited range of 0.2 to 0.4 magnitudes per air mass (the
program normally uses 0.3 as a "standard" value). The difference
between rural and urban skies is represented by a sky pollution
brightness ("BC") which he says can vary from 0 to 1,000,000
nanoLamberts (equivalent to 11.3 magnitudes per square arc second; the
program uses 0 as the "standard" value).
I have some experience with other publications by Dr. Schaefer and
have reasons to be a bit suspicious of his claims and ideas, but he
says the program was tested against a database of 1,739 observations
from H. J. J. Bulder, and found to be reliable to +/-0.3 mag (the
details of the testing, how he knew the values of the 16 variables for
all those observations, and the range over which they were tested is
not explained).
The article includes an illustration indicating that for a ~71%
illuminated Moon (the kind expected at the time of LCROSS impact on
2009 Oct 9 at 11:30 UT) Schaefer predicts his "standard" observer
using a 6-inch telescope under "standard" conditions could visually
observe the occultation of a magnitude 8.5 star at the center of the
dark limb, and a magnitude 5.0 star at the center of the bright limb.
He also believes the same observer could detect a magnitude 5.0 star
up to the dark limb in daylight (Sun 10° above the horizon -- a
condition less favorable than that for US East Coast observers of the
LCROSS impact).
In the article Schaefer refers to the natural light from the Moon
scattered in the sky as the "glare" (apparently calculated on lines
580-670 of the program and not to be confused with the internal
telescope glare mentioned as a major problem by you and Derek). It is
unclear if the program is intended to apply to the case of a bright
point very near one of the Moon's cusps (which would seem most
relevant to the LCROSS impact). The magnitude of the "glare" appears
to vary with the cusp distance "C" (in degrees), but examination of
the listing indicates it would have a divide by zero error (on lines
790 and 800) if one entered a value of C=0; and for values slightly
different than that it flips between the possibly quite different
"bright limb" and "dark limb" estimates.
-- Jim
On Aug 28, 6:21 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> On Aug 27, 7:47 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> <snip all>
>
> On the question of the faintest star visible before occultation on the
> bright limb, it appears that Dr. Schaefer did an popular article on
> this in S&T in 1993, summarizing his 1991 article. It was also turned
> into one of the S&T BASIC programs available via the internet.
>
> Schaefer, B. E. A star's visibility just before occultation. Sky
> Telesc., Vol. 85, No. 1, p. 89 - 91 (S&T Homepage) Bib. Code
> 1993S&T....85...89S
>
> url:http://adsabs.harvard.edu/abs/1993S%26T....85...89S
>
> S&T DOS Program from 1993http://media.skyandtelescope.com/binary/occvis.bas
>
> How to run a DOS QBasic program on a Windows XP Computerhttp://www.skyandtelescope.com/community/hobbyqanda/3399826.html
cano...@yahoo.com
report later. In Schaefer's visibility alogrithms, stars are
perceived as extended objects above about 100 mag - which is the case
if you look at any star using a 4mm eyepiece and a reasonable focal
lenght.
The main limitation in the program is that he assumes a sky free of
light pollution. Variable "BC" for light pollution is set to zero.
The value of light polluted skies will need to be determined in
nanoLamberts. Difficult but not impossible. Setting it to something
more reasonable will change the result signficantly.
Perhaps the S&T people on the list can discuss the matter direclty to
Dr. Schaefer.
- Kurt
>
> - Show quoted text -
Derek C Breit
Much easier and faster to actually DO lunar occultations, since it will be
highly dependant on your personal equipment..
Glare, probably more accurately termed "field flooding", will always be the
primary issue. Assuming the weather is good.
I did just successfully record to video a mag 8.8 star (combined light from
a close double) on a 75% lit moon, at an altitude of 20 degrees, at a cusp
angle of 12 North. Being closer to the brightly lit cusp made this
exponentially more difficult the mag 9.3 star at 19N.
I'll try to create a decent video or still image and post it to my website
tomorrow. It will be very ugly to many, but data is a thing of beauty to
me.. Other than posting a link to the video, I'll be done interjecting on
this subject..
Derek
cano...@yahoo.com
> On Aug 27, 7:47 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> <snip all>
the faintest star visible just above the lunar limb, I adapted the
Schaefer lunar occulation program with parameters for the LCROSS Oct.
9 impact as viewed from Salt Lake City, Utah using a 10 inch Newtonian
scope. Schaefer's occultation limiting magnitude program predicted
that the faintest visible star just before occultation was 5.3 mags
for my scope. This corresponds to a sky brightness of 19.7 MPSAS.
Since the LCROSS team predicts the maximum brightness of the LCROSS
impact cloud at 3.0 MPSAS, there is a good contrast index (6.6)
between the moonlight glare sky-brightness just above the limb and the
ejecta cloud.
This modeling suggests that the LCROSS ejecta cloud should be visible
in 10 inches of aperture notwithstanding the lunar glare problem.
A web document explains how to set the parameters in the Schaefer
lunar occultation limiting magnitude program to emulate the LCROSS
impact cloud and observing conditions for your observing point.
http://members.csolutions.net/fisherka/astronote/observed/LCROSS/SchaeferOccultationCalculatorValuesLCROSS.html
http://tinyurl.com/mrasdn
I have also made a modified the S&T DOS program to set the parameters
for Salt Lake City observing circumstances. This can be used as a
template for your local circumstances.
http://members.csolutions.net/fisherka/astronote/observed/LCROSS/occvis_slcut.bas
http://tinyurl.com/l38vj9
This note reports the result is a model prediction and and not an
actual measurement.
The next date that the Moon will be illuminated at 71% and in a manner
similar to the LCROSS impact is on Sept. 9 at 11UT (Sept. 9 at 5am
MDT, 77%)) and Sept. 10 11UT (Sept. 10, 5am, 68%):
Source: LTVT ephemeris data, topocentric W111.8 N41.8
Date-TimeUT libr_lat lib_long colong illumfrac
20090907 1130 -6.2 -5.5 128 92
20090908 1130 -6.2 -5.5 140.2 85.5
20090909 1130 -6.1 -5.4 152.3 77.3
20091009 1130 -3.5 2.8 158.2 70.9 Impact day
20090910 1130 -5.4 -5.1 164.4 67.7
20090911 1130 -4.4 -4.3 176.5 57.1
20090912 1130 -3.2 -3.3 188.7 45.8
Date-TimeUT Lunar age (days)
20090907 1130 18.1
20090908 1130 19.1
20090909 1130 20.1
20091009 1130 20.6 Impact day
20090910 1130 21.1
20090911 1130 22.1
20090912 1130 23.1
MDT) in Salt Lake City, the Moon will be an altitude much closer the
circumstances of impact - around 70 degrees. On Sept. 9 at 11:21UT
there is graze of the north pole by ZC387 (SAO75476, HD16302 in Aries
between Hamal and Botein), but at magnitude 6.9, it is too faint to be
observed visually according to the Schaefer predicted model as it
passes along the bright limb side. But as the star passes the pole
and crosses a degree or two into the dark limb, it should become
visible. I may run a test to see if SAO75476 can be observed or
imaged. I will also be looking to see if the grazing star's visibiliy
is consistent with Schaefer's model - it should not be visible until
it just crosses to the dark limb.
Occult 4 data for this graze is:
Grazing Occultations near SaltLakeCity UT
E. Longitude -111 53 24.0, Latitude 40 45 24.0, Alt. 1337m;
Telescope dia 15cm; dMag 0.0
day Time P Star Sp Mag Mag % Elon Sun Moon Cusp
angle Distance Azimuth Path formula
y m d h m s No D v r V ill Alt
Alt o km
09 Sep 9 11 21 38 Gr 387cG5 6.9 6.4S 77- 123 69 ** GRAZE:
CA 2.7N; Dist. 19km in az. 339deg. [Lat =40.94+0.29(E.Long+111.89)]
(For Utah locals: The graze coordinates across I-15 from the
Farmington Bay Water Fowl Management Area, near either the Centerville
Recreation Complex or Smoot Park).
On August 28, the Moon was illuminated at 71% but reversed as to what
will occur on impact on Oct. 9. Salt Lake was overcast and I was
unable to take any images from which to make differential photometry
measurements.
The take away point is that based on this modelling of the lunar glare
brightness above the south lunar pole on Oct. 9, even if LCROSS ejecta
cloud has a brightness of 6 mpsas, the ejecta cloud should still have
sufficient contrast against the lunar glare at the south pole should
not prevent observing the cloud.
This is an amateur note. Corrections and criticisms to the above are
welcomed.
Clear Skies - Kurt
cano...@yahoo.com
magnitude program. The catch is when you play with the parameters is
at high magnification there is a discontinuous break in the limiting
magnitude as you cross between dark and bright limbs. In my
simulation of the LCROSS impact circumstances for my 10 inch Newt at
300 power, the limiting magnitude of a star a few degrees on the
bright limb side is 5.3 mags; a few degrees the dark limb side and the
predicted visual limiting magnitude drops to 9.2 mags. For the
predicted impact time, only Faustini is on the dark limb side; the
other targets are few cusp degrees on the bright limb side. The break
may reflect the limits of the model; it may reflect the actual
observing situation. - Happy imaging - Kurt
> a close double) on a 75% lit moon, at an altitude of 20 degrees, at a cusp
> angle of 12 North. Being closer to the brightly lit cusp made this
> exponentially more difficult the mag 9.3 star at 19N.
Derek C Breit
Kurt-
This graze should be fairly easy to see visually in a 10" scope, even though
the prediction is for a 6"..
Since you are using Occult, generate the actual graze details, and read off
the visibility table provided..
First Off.. This is a double star, so this is a combined magnitude of 6.9...
387 is double:
AB 7.7 7.7 0.10" 90.0 () Graze path of B 0.08 km north, and 0.2 secs
later compared to A
And here are a couple of the visibility tables.. You will note that a 2/10s
of a degree change is Cusp Angle provides a 0.3 mag gain in the Limiting
Mag.. Your Posted prediction was for a CA of 2.7N..
At longitude -111.75:
Limiting Magnitudes for various telescope apertures (in cm)
CA\Tdia 5 10 15 20 25 30 35
-1.4 2.8 4.2 5.0 5.5 5.8 6.1 6.2
0.6 2.8 4.2 5.0 5.5 5.8 6.1 6.2
2.6 4.0 5.5 6.3 6.8 7.1 7.4 7.6
4.6 4.8 6.2 7.0 7.6 7.9 8.2 8.4
6.6 5.0 6.4 7.2 7.7 8.1 8.4 8.6
At longitude -112.25:
Limiting Magnitudes for various telescope apertures (in cm)
CA\Tdia 5 10 15 20 25 30 35
-1.2 2.8 4.2 5.0 5.5 5.8 6.1 6.3
0.8 2.8 4.2 5.0 5.5 5.8 6.1 6.3
2.8 4.3 5.8 6.6 7.1 7.4 7.7 7.9
4.8 4.8 6.2 7.0 7.6 7.9 8.2 8.4
6.8 5.1 6.5 7.3 7.8 8.2 8.5 8.7
This change is extremely important and I have talked about it repeatedly.
You have to have separation from a brightly lit feature to have any chance.
It is plain as day in the tables above. They are not perfect tables, as some
scopes have less glare and some detectors are better than others.. This also
matches what I did last night when I videotaped the disappearance of a mag
9.3 star at a cusp angle of 12 with a 30cm. 1/60s exposures, Time inserted
with a KIWI OSD, and graphed out with LiMovie. Timing +/- 0.008s. Report
sent (to me)..
Distance from a lit feature is everything.
This is why, when the LCROSS Principals end up with two possible impact
sites, heavy weighting in the decision making process needs to be given to
the site furthest from any lit feature..
From an amateur point of view, it should be the entire point after the
technical needs of the mission.
Derek
PS.. As IOTA's Lunar Occultation Coordinator, I would point out that any
timings of that star you mention is much sought after, especially since it
is double. We have a new goal of determining separations and PA's of Double
Stars. As an OCCULT User, I am sure you know this. I mention it for others
following along.
cano...@yahoo.com
Being a novice at occultations, I was not aware of the secondary
report built into Occult 4. Thanks for pointing it out.
The limiting magnitude data appears consistent with Schaefer's model
for my 10 inch Newt:
CA LM for 250mm
-1.1 5.8
0.9 5.8
2.9 7.6
4.9 7.9
6.9 8.2
Since Schaefer's article in S&T mentions he has preparing his program
with respect to the IOTA, perhaps it is incorporated into Occult 4?
I'll see what I can do recording the event including trying to work up
some interest at my local club. I do not have KIWI OSD being a
novice, but use an audio recording of the shortwave time signal.
But this year, it's been Bad Weather - 10; Observer - 2 for successful
scheduled observing events.
> This is why, when the LCROSS Principals end up with two possible
> impact sites, heavy weighting in the decision making process needs
> to be given to the site furthest from any lit feature..
team's chart implies, it looks like there is enough margin for error
even if the cloud is a bit on the bright side.
Clear Skies - Kurt
On Aug 30, 10:22 pm, "Derek C Breit" <breit_id...@hotmail.com> wrote:
> Kurt-
>
> This graze should be fairly easy to see visually in a 10" scope, even though
> the prediction is for a 6"..
> PS.. As IOTA's Lunar Occultation Coordinator, I would point out that any
> timings of that star you mention is much sought after, especially since it
> is double. We have a new goal of determining separations and PA's of Double
> Stars. As an OCCULT User, I am sure you know this. I mention it for others
> following along.
Derek C Breit
I don't know if OCCULT is using Schaefer's model or something unique. I
will find out about that..
Mag 5.3 on the bright limb?? I wouldn't even try it, but then again I would
not try any occultation visually since I aim to accurately time them. Any
CCD detector, whether a Sony style interlaced video chip, or an SBIG style
"real" CCD has to fight irradiation of the bright limb, which makes the
apparent bright limb extend out from it's nominal position. So you may see
the star on the bright limb disappear on camera, but it reality it can be a
sizeable distance from the limb. Usually it just melds into the brightness
and never disappears. Different on thin crescents and fat gibbous Moons
too..
Test, Test, and more tests by occultation..
300X Visually on a 10"?? I am using a 12" f/10 SCT @ 1920mm focal length
with a Watec 1/2" chip video camera and see almost 1/4 of the full lunar
disc..
***For the predicted impact time, only Faustini is on the dark limb side;
the other targets are few cusp degrees on the bright limb side.***
If not Faustini, then the ejecta needs to move a decent distance away (in
arc seconds).
Derek
PS.. Does this list allow attachments??
cano...@yahoo.com
get about the same TFOV when using a 4mm lens on a 1200mm fl scope.
It's hard on the eyes, so after a few minutes, I generally drop back
to a 6mm lens (200x) or 9mm (133x).
> PS.. Does this list allow attachments??
it does not allow attachments.
- Kurt
Derek C Breit
Hi Kurt- SEE BELOW
Thanks, Derek.
Being a novice at occultations, I was not aware of the secondary report
built into Occult 4. Thanks for pointing it out.
>>> In Occult, the right click is your friend. I am a beta tester, so
anything you need assistance with, feel free to email me directly. Anytime..
If I am answering a question, I am less likely to be irritating some email
group..
We need to talk anyway so I can add you into the observer database, if you
are not there already..
Since Schaefer's article in S&T mentions he has preparing his program with
respect to the IOTA, perhaps it is incorporated into Occult 4?
>>> Probably and I have inquired about this already..
I'll see what I can do recording the event including trying to work up some
interest at my local club. I do not have KIWI OSD being a novice, but use
an audio recording of the shortwave time signal.
>>> That works just fine for a graze or a total occultation, but for us to
work on the PA and Sep of double stars, a video recording is a must (with
WWV or CHU on the audio track for timing).
And by "US" I mean those guys over there.. I am but an enthusiast data
gatherer..
Derek
Derek C Breit
That explains it.. It is why I went from visual to video in about 48 hours
after my first event. That's actually a good story I'll tell you someday..
But I am emailing for this...
While duplicating your graze prediction with the current as yet unreleased
next version, I generated an error.. I just got this back as part of a
conversation on the error..
-------------------
On a related issue......... In this case ZC387 is listed as a double star.
However there is no
entry in either the WDS or the Interferometric catalogues for this star. It
is flagged because
it was included in David D's dsFile several decades ago. DavidD will be
reviewing such stars
over the next month...
Dave Herald
Canberra, Australia
-------------------
So, you may decide it isn't really worth trying.. Or you could be like me
and set three alarms and a messaging service so as to not miss this event so
you could find out.. Possibly something in between?? :-))
Certainly still a good visibility test as a single star of course..
Is your scope mobile and do you want to be in the actual graze zone?? I can
do that via direct emails..
Derek
PS.. Forgive us Group (OK me) for this little chat session!
cano...@yahoo.com
> On Aug 28, 7:21 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> > On Aug 27, 7:47 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> > The 1993 S&T DOS program by Bradley Schaefer can be used to predict
> the faintest star visible just above the lunar limb, I adapted the
> Schaefer lunar occulation program with parameters for the LCROSS Oct.
I have made a substantial revision to my modification of the Schaefer
1993 Qbasic program for model sky brightness in mpsas at the lunar
limb during the LCROSS impact.
The revised Qbasic program is available at:
http://members.csolutions.net/fisherka/astronote/observed/LCROSS/occvis_slcut.bas
http://tinyurl.com/l38vj9
An instruction sheet and parameter entry tips are at:
http://members.csolutions.net/fisherka/astronote/observed/LCROSS/SchaeferOccultationCalculatorValuesLCROSS.html
http://tinyurl.com/mrasdn
The correction fixes computation errors and the model now responds to
light pollution inputs.
Modeling analysis using the modified Qbasic program indicates that
just on the bright side of lunar polar termination and just above the
polar limb, sky brightness will be about 14.7 MPSAS. This is a
favorable contrast with the LCROSS team's single frequency brightness
of the ejecta curtain at 3.0 mpsas. Based on this modeling, lunar
glare should not prevent observing or imaging the LCROSS impact. But
this is a model, not real data. Confirmation of the level of lunar
glare above the south lunar pole by imaging-based differential
photometry on Sept. 9 is recommended.
Modeling indicates that light pollution in an urban environment may be
a factor reducing one's ability to see the ejecta curtain. It is
recommended that observer travel to rural or dark sky sites to observe
the impact.
Corrections and criticisms on the modified model are welcomed.
Clear Skies - Kurt
cano...@yahoo.com
> So, you may decide it isn't really worth trying..
9, so I am already committed to going.
Would you like me to do this as an occultation off the graze path to
check for a double or would you lke a graze to map the limb?
> Is your scope mobile and do you want to be in the actual graze zone??
> I can do that via direct emails..
pass the Google error message.)
http://members.csolutions.net/fisherka/astronote/observed/LCROSS/ZC387_2009_Sep__9.htm
The graze path runs through a remote basin and range valley 60
kilometers west of Salt Lake called Skull Valley and near a local
prominent feature - Skull Valley Rock. There is a convenient dirt
road that runs perpendicular to the graze path.
My commitment is for myself only, but an officer of my local club is
also a member on this newsgroup, so I will see if there is any
interest in my local club in running a multiple scope graze line.
A reminder email around Sept. 6 would be welcomed.
Clear Skies - Kurt
> PS.. Forgive us Group (OK me) for this little chat session!
cano...@yahoo.com
> On Aug 30, 9:32 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> > On Aug 28, 7:21 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> > > On Aug 27, 7:47 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
The predicted 14.7 mpsas at the limb for the LCROSS impact is similar
to the Earthshine mpsas for the 60 to 80 phase angle reported in the
Earthshine paper that Chris mentioned. Maybe just a coincidence. -
Kurt
See http://www.iac.es/folleto/research/preprints/files/PP07047.pdf
Derek C Breit
Would you like me to do this as an occultation off the graze path to check
for a double or would you like a graze to map the limb?
>>>>> BOTH.. Grazes tend to extend the time between possible events, making
double stars more obvious..
I already have the Google Earth graze map run off. (Click twice to pass the
Google error message.)
http://members.csolutions.net/fisherka/astronote/observed/LCROSS/ZC387_2009_
Sep__9.htm
>>>>>This is a very good try, but I am betting it is incorrect by a decent
amount because it was done for the proper elevation. That's just a guess.
I'll make you an elevation adjusted map.. And provide a profile for you..
The graze path runs through a remote basin and range valley 60 kilometers
west of Salt Lake called Skull Valley and near a local prominent feature -
Skull Valley Rock. There is a convenient dirt road that runs perpendicular
to the graze path.
>>>>>> Please open either your map or preferably one of mine...
Any GoogleMap link on this page.. http://www.poyntsource.com/New/Global.htm
Zoom into the place you mention above.. The dirt road.. Zoom in as much as
possible, and put the cursor on that road and double left click.. Cut and
paste the line of text that appears under the map, namely the coordinates,
into an email to me and include the next item as well..
Zoom back out to a reasonable level and click the button on the map at the
top right that says TOPO and, zooming in an out as needed, ascertain the
elevation of this site, which shown in feet.. Send that too..
Please..
My commitment is for myself only, but an officer of my local club is also a
member on this newsgroup, so I will see if there is any interest in my local
club in running a multiple scope graze line.
>>>>> Two observers.. OK..
A reminder email around Sept. 6 would be welcomed.
>>>>> Wow.. Should I fly to Utah and observe it for you too?? .. Man..
That's good humor there..
I believe I have an observer in that area I could send you.. I will find
out.. It would be REAL good to put a video observer between two visual
observers..
Derek
Derek C Breit
Google error message.)
--------------------------------
FYI- The OCCULT Helpfile and the actual HTML of those maps, specifically
warn potential editors of the coding to let me know first before editing
them. They are very temperamental..
I mention this since you like to do programming, and at some point you will
want to enter in a newly acquired Google Key..
Derek
PS.. Corrected Sentence...
I am betting it is incorrect by a decent amount because it *WASN'T* done for
the proper elevation. That's just a guess. I'll make you an elevation
adjusted map.. And provide a profile for you..
I have a spell checker. I do not have an Idiot Typer checker..
Derek C Breit
Kurt-
You do know about this page I do for S. L. City, right???
http://www.poyntsource.com/New/Regions/Wiggins.htm
Derek
cano...@yahoo.com
v4 till I can match the result. Please send it on. - Clear Skies Kurt
Derek C Breit
> That's just a guess. I'll make you an elevation adjusted map..
Thanks, Derek. With one done the right way I can work on it in Occult v4
till I can match the result. Please send it on. - Clear Skies Kurt
----------------------------------------------------------------------------
----------
There is no need to match this result.. This will still not be "correct"
unless I got lucky..
( I can show you how to do this anytime.. )
All the data...
http://www.poyntsource.com/New/Requested_Profiles.htm
The GoogleMap..
http://www.poyntsource.com/New/Google.htm
Right hand column - Salt Lake City..
Open the map and change the +15.0 box to 1500 and press the button.. This
moves one offset line out of the way..
Set the other line to +1.0.. Press the button..
The Green line is altitude adjusted for 1306 meters. The Grey line is the
line to observe from.. Find where it intersects that spot your were telling
me about before.. The Perpendicular dirt road in Skull Valley.. Put the
cursor on the intersection of the line and road and double left click and
send me the coordinates that appear under the map.. (Scroll Down).. Also the
elevation at that spot using the TOPO button..
I do have an observer less than 20 km from there in case you want to
converse with him in person..
ALSO.. It finally dawned on me.. This is a graze thru my front yard, the
second one in the year I have lived here..
Derek
Derek C Breit
Magnitude table
The magnitude visibility table gives the faintest magnitude that will be
visible at that cusp angle with different telescope apertures, assuming good
observing conditions. An example of the table is:
At longitude 40.00:
Limiting Magnitudes for various telescope apertures (in cm)
CA\Tdia 5 10 15 20 25 30 35
1.7 2.8 4.1 4.9 5.3 5.5 5.7 5.8
3.7 4.5 5.9 6.7 7.1 7.4 7.6 7.8
5.7 4.7 6.1 6.8 7.3 7.6 7.8 7.9
7.7 5.4 6.8 7.5 8.0 8.3 8.5 8.7
9.7 5.4 6.8 7.5 8.0 8.3 8.5 8.7
The first line gives the longitude along the graze path used for the
generation of the table. You can generate the table for any location along
the path and this can be important to allow for changes in cusp angle, or
star altitude.
The third line of the table provides column headers. CA is the Cusp Angle of
the star. Tdia refers to Telescope diameter (in cm) which, in the 7 columns
of the body of the table cover telescope apertures from 5cm to 35 cm.
The 5 lines of the body of the table correspond to the cusp angle of the
star. The third line is set as the Cusp Angle of the graze at the selected
longitude [or at the mid-point of the listed graze path in the prediction.]
The preceding and following lines can be used in conjunction with the graze
profile to indicate visibility of the star during the course of the graze.
The organiser of a graze expedition can use this table to:
Indicate the minimum telescope aperture required to observe the graze
(Either the whole graze. Or just one half of a graze that is close to the
cusp); and
Allocate sites to observers, in a way that maximises the number of
successful timings made during the graze.
Assume for this example that the star was of magnitude 5.0. This table
indicates that the part of the graze that occurs furthest from the cusp will
be visible in almost any telescope. However, when the star is close to the
cusp, it will be more difficult to observe and might require a 20cm (8")
telescope. The organiser might locate observers with medium-size telescopes
closest to the graze limit confident that they will see all events because
the star will always be some distance from the cusp. They might locate
observers with large telescopes further in from the graze path, in the
knowledge that they will be able to record the whole graze because with
their telescope they will be able to see the star when it is close to the
cusp. They might also locate observers with small telescopes in a similar
region to the large telescopes in the expectation that they will not see the
star while it is near the cusp, but will have no difficulty with the part of
the graze where the star is a long way from the cusp (when would in fact be
easier to see than if the observer was located closer to the graze path.)
[The expression used by OCCULT is that of Schaefer, B. E., Bulder, H. J. J.,
and Bourgeois, J., Lunar occultation visibility, Icarus , 100, 60-72 (1992)
]
cano...@yahoo.com
Patrick about a second scope. - Clear Skies Kurt
On Sep 1, 12:56 am, "Derek C Breit" <breit_id...@hotmail.com> wrote:
> > That's just a guess. I'll make you an elevation adjusted map..
>
> Thanks, Derek. With one done the right way I can work on it in Occult v4
> till I can match the result. Please send it on. - Clear Skies Kurt
>
> There is no need to match this result.. This will still not be "correct"
> unless I got lucky..
> ( I can show you how to do this anytime.. )
>
> All the data...http://www.poyntsource.com/New/Requested_Profiles.htm
>
Derek C Breit
Patrick about a second scope. - Clear Skies Kurt
cano...@yahoo.com
cano...@yahoo.com
Schaefer, B. E., Bulder, H. J. J., and Bourgeois, J., Lunar
occultation visibility, Icarus , 100, 60-72 (1992)