LCROSS Imaging Presentation for Review
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dave_dockery
Sep 8, 2009, 12:00:08 PM9/8/09
to LCROSS_Observation
I'm giving a talk on imaging the LCROSS impact for the White Sands
Star Party this weekend and I'm hoping some of you can review it to
make sure I'm not way off-base. I've tried to pull together info from
the NASA and NMSU sites as well as the excellent info shared on this
group.
Please look it over and let me know if there are problems. It's been
uploaded to the files section and is called "Imaging the LCROSS Impact
Event DRAFT.pdf"
Thanks much,
Dave
Dave Dockery
Las Cruces, NM.
http://home.comcast.net/~dave.dockery/
Star Party this weekend and I'm hoping some of you can review it to
make sure I'm not way off-base. I've tried to pull together info from
the NASA and NMSU sites as well as the excellent info shared on this
group.
Please look it over and let me know if there are problems. It's been
uploaded to the files section and is called "Imaging the LCROSS Impact
Event DRAFT.pdf"
Thanks much,
Dave
Dave Dockery
Las Cruces, NM.
http://home.comcast.net/~dave.dockery/
cano...@yahoo.com
Sep 8, 2009, 8:01:36 PM9/8/09
to LCROSS_Observation
On Sep 8, 10:00 am, dave_dockery <dadock...@gmail.com> wrote:
> Please look it over and let me know if there are problems.
Slide 7: On Friday, the Saturday before you talk, the LCROSS team will
> Please look it over and let me know if there are problems.
announce the final target.
Slide 8: "The plume is only projected to be ~ 5 -10" highand ~17" wide
at final detectable extent (dims as it grows)"
Chas Miller, who prepared the image you show in Slide 8, stated in a
message here:
"Glad to see you are taking an interest in LCROSS observations. I
just
wanted to point out that given the factor of 1.78 km/arcsec at time
of
impact, to convert an estimated plume height in km to arseconds, one
should divide by 1.78. So, for an estimated plume height of 10 km,
this
would translate to 10/1.78 or 5.6 arcseconds. A plume only 3 km high
will
be 1.7 arcseconds (tiny!).
Given a diameter of 17 km for crater Newton E, the angular diameter
will
be 17/1.78 or 9.6 arcseconds. That is about half the 20" ruler in the
images we posted (the scale was drawn in Powerpoint - not precisely
accurate, but should be fairly close)."
http://groups.google.com/group/lcross_observation/msg/7c14e92f172fe4e8
The values you quote above are for a max scenario cloud. I would talk
about both clouds, including the 95% certainty cloud mentioned in
Chase Miller's computations.
The "1/3 the size of Jupiter analogy" in the LCROSS Citizen Science
"About" page also makes size question easy to understand.
Slide 12: If you have an internet connection or a direct TV dish
uplink to NASA TV at your star party, the DSLR guys can know exactly
when the impact occurs and trigger their shutters at the right
moment. Similarly, with such knowledge of the precise moment of
impact, the video and avi capture guys can cut down on that
recommendation for 10 minutes of imaging and not eat up so much disk
space.
Slide 13: "Free processing software like Registax . . . "
You've said it in your slide, but I would beef up the text to clarify
that you mean making a gif movie after selecting the sharpest frames
of the evolving cloud in Registax. Just applying Registax in
autoprocessing mode will probably just erase the ejecta cloud.
Once you have finalized the presentation (or maybe after you have
presented it and can tweak it based on audience questions), please
post a link to the final back here with GNU permission for other clubs
to reuse it.
Clear Skies - Kurt
P.S. - I like the Three Stooges picture on Slide 12.
Jim Mosher
Sep 9, 2009, 8:05:25 PM9/9/09
to LCROSS_Observation
Dave,
That's a really excellent presentation! It must have taken a lot of
work to put together.
One very trivial thing that caught my eye was the frequently repeated
word "impacter". My eyes have become so accustomed to seeing it
spelled "impactor" in all the other LCROSS-related literature that I
wondered if you might have made a typo. I checked my Random House
unabridged dictionary and it lists your spelling as the preferred one,
although "impactor" is also used; Webster's lists them in the opposite
order; Google finds an equal number of usages each way.
More substantively, I doubt that anyone in your audience will have
time to "do the math", but if they did they would notice a serious
discrepancy between the "Ejecta Dust Column Density" plot versus the
"4-6 magnitudes per arcsec-squared" values list on your "Brightness
Slide" (page 9 of the PDF). The dust model seems to be saying that
even in its densest parts (with projected dimensions of a few
kilometers), the plume will be presenting only 750,000 particles per
square meter (mislabeled "#/m^3") to the line of sight. According to
the article by Summy et al. from which this figure seems to be taken
(or at least in which it is repeated):
http://adsabs.harvard.edu//abs/2009LPI....40.2267S
the particles used in the model are "70 microns" (presumably in
diameter). That would give each a cross section of 3.8x10^-9 m^2 per
particle. Multiplying the two numbers together indicates they would
occupy only about 0.003 of the available space (in 0.997 of the
available space we would see between them to whatever background is
behind). Assuming the dust particles are spherical, on average, they
could be thought of as acting as mini-Moons, and collectively, at this
phase, they would be expected to have ~0.003 the surface brightness of
the real Moon (taken as whole). Montanes-Rodriguez et al. (2007) of
Big Bear Solar Observatory's Project Earthshine:
http://bbso.njit.edu/Research/EarthShine/bibliography.htm
put that value (averaged over the Moon at this phase) at about 4.8
mpsas. In the peculiar reversed logarithmic system astronomers
prefer, when reduced by a factor of 0.003, the estimated surface
brightness of the swarm of mini-Moons at their *densest places*
becomes something on the order of 11 mpsas. On might argue that the
excavated material will be fresher and less porous than the normal
lunar surface, and hence will have a higher reflectance, but it is
unlikely to be so by more than a factor of 2 or 3, which would modify
the estimate by only about 1 mpsas (to perhaps 10 mpsas).
As a result, one has to wonder if there is something wrong with the
column density chart, or with the estimate of 4 to 6 mpsas surface
brightness given on your slide...
The recommendation to set the exposure based on a star of magnitude 8
or 9 is equally questionable, in my mind. The Moon itself is likely
to be a much more reliable photometric standard, especially for
imaging extended objects; but exactly how the exposure should be set
will have to await Friday's announcement of the viewing geometry, and
hopefully some clarification from the LCROSS team of the expected
surface brightness. In the absence of any further guidance, about all
imagers can do is to turn up the gain to a high level hoping to see
the first signs of the cloud, and if something *is* seen, and actually
develops into a surface brightness of 4 to 6 mpsas, to be prepared to
turn the gain down quickly so it doesn't saturate. Note that 4 mpsas
is roughly the same as the average surface brightness of the bright
sunlit part of the Moon at this phase, and possibly as bright or
brighter than anything else near the poles. It is as bright as Mars
(3.9 mpsas). 6 mpsas is about midway between the surface brightness of
Jupiter (5.6 mpsas) and Saturn (6.9 mpsas).
Your illustration of Saturn near the saturated bright limb of the Moon
on the next slide is excellent, provided you are prepared to identify
the Moon's phase and the ratio of surface brightnesses it represents.
The suggestion on the "Strategies" page to experiment with methods of
reducing stray light is also good. If the plume is as bright as Mars
or Jupiter this shouldn't be necessary, but if it is extremely dim (as
seems possible), everything will help. The strategies that work for
each observer's setup may be different, and it should be possible to
experiment in the next month on targets other than the Moon: for
instance a streetlight, light-bulb, or of other light source
subtending an angle similar to the Moon, attempting to detect detail
in adjacent dimmer areas (ideally of known intensity ratio). I myself
found that with an older 4-inch Maksutov, enlarging the secondary
obstruction, and stopping down the aperture, with black construction
paper produced no obvious improvement in such a streetlight test,
certainly not enough improvement to justify the loss of light.
Unfortunately, with such vague and discrepant estimates of the
expected plume surface brightness relative to the sunlit Moon we don't
know how much improvement (if any) we may need to achieve.
Again, an excellent presentation to which the above comments are minor
amendments.
-- Jim
That's a really excellent presentation! It must have taken a lot of
work to put together.
One very trivial thing that caught my eye was the frequently repeated
word "impacter". My eyes have become so accustomed to seeing it
spelled "impactor" in all the other LCROSS-related literature that I
wondered if you might have made a typo. I checked my Random House
unabridged dictionary and it lists your spelling as the preferred one,
although "impactor" is also used; Webster's lists them in the opposite
order; Google finds an equal number of usages each way.
More substantively, I doubt that anyone in your audience will have
time to "do the math", but if they did they would notice a serious
discrepancy between the "Ejecta Dust Column Density" plot versus the
"4-6 magnitudes per arcsec-squared" values list on your "Brightness
Slide" (page 9 of the PDF). The dust model seems to be saying that
even in its densest parts (with projected dimensions of a few
kilometers), the plume will be presenting only 750,000 particles per
square meter (mislabeled "#/m^3") to the line of sight. According to
the article by Summy et al. from which this figure seems to be taken
(or at least in which it is repeated):
http://adsabs.harvard.edu//abs/2009LPI....40.2267S
the particles used in the model are "70 microns" (presumably in
diameter). That would give each a cross section of 3.8x10^-9 m^2 per
particle. Multiplying the two numbers together indicates they would
occupy only about 0.003 of the available space (in 0.997 of the
available space we would see between them to whatever background is
behind). Assuming the dust particles are spherical, on average, they
could be thought of as acting as mini-Moons, and collectively, at this
phase, they would be expected to have ~0.003 the surface brightness of
the real Moon (taken as whole). Montanes-Rodriguez et al. (2007) of
Big Bear Solar Observatory's Project Earthshine:
http://bbso.njit.edu/Research/EarthShine/bibliography.htm
put that value (averaged over the Moon at this phase) at about 4.8
mpsas. In the peculiar reversed logarithmic system astronomers
prefer, when reduced by a factor of 0.003, the estimated surface
brightness of the swarm of mini-Moons at their *densest places*
becomes something on the order of 11 mpsas. On might argue that the
excavated material will be fresher and less porous than the normal
lunar surface, and hence will have a higher reflectance, but it is
unlikely to be so by more than a factor of 2 or 3, which would modify
the estimate by only about 1 mpsas (to perhaps 10 mpsas).
As a result, one has to wonder if there is something wrong with the
column density chart, or with the estimate of 4 to 6 mpsas surface
brightness given on your slide...
The recommendation to set the exposure based on a star of magnitude 8
or 9 is equally questionable, in my mind. The Moon itself is likely
to be a much more reliable photometric standard, especially for
imaging extended objects; but exactly how the exposure should be set
will have to await Friday's announcement of the viewing geometry, and
hopefully some clarification from the LCROSS team of the expected
surface brightness. In the absence of any further guidance, about all
imagers can do is to turn up the gain to a high level hoping to see
the first signs of the cloud, and if something *is* seen, and actually
develops into a surface brightness of 4 to 6 mpsas, to be prepared to
turn the gain down quickly so it doesn't saturate. Note that 4 mpsas
is roughly the same as the average surface brightness of the bright
sunlit part of the Moon at this phase, and possibly as bright or
brighter than anything else near the poles. It is as bright as Mars
(3.9 mpsas). 6 mpsas is about midway between the surface brightness of
Jupiter (5.6 mpsas) and Saturn (6.9 mpsas).
Your illustration of Saturn near the saturated bright limb of the Moon
on the next slide is excellent, provided you are prepared to identify
the Moon's phase and the ratio of surface brightnesses it represents.
The suggestion on the "Strategies" page to experiment with methods of
reducing stray light is also good. If the plume is as bright as Mars
or Jupiter this shouldn't be necessary, but if it is extremely dim (as
seems possible), everything will help. The strategies that work for
each observer's setup may be different, and it should be possible to
experiment in the next month on targets other than the Moon: for
instance a streetlight, light-bulb, or of other light source
subtending an angle similar to the Moon, attempting to detect detail
in adjacent dimmer areas (ideally of known intensity ratio). I myself
found that with an older 4-inch Maksutov, enlarging the secondary
obstruction, and stopping down the aperture, with black construction
paper produced no obvious improvement in such a streetlight test,
certainly not enough improvement to justify the loss of light.
Unfortunately, with such vague and discrepant estimates of the
expected plume surface brightness relative to the sunlit Moon we don't
know how much improvement (if any) we may need to achieve.
Again, an excellent presentation to which the above comments are minor
amendments.
-- Jim
dave_dockery
Sep 9, 2009, 10:59:25 AM9/9/09
to LCROSS_Observation
Hi Kurt,
Thanks for the good suggestions. I do have a question though.
> Slide 8: "The plume is only projected to be ~ 5 -10" highand ~17" wide
> at final detectable extent (dims as it grows)"
<snip>
those.
> Once you have finalized the presentation (or maybe after you have
> presented it and can tweak it based on audience questions), please
> post a link to the final back here with GNU permission for other clubs
> to reuse it.
You bet
> P.S. - I like the Three Stooges picture on Slide 12.
I love that picture. You have to wonder what disaster they're looking
at on the floor. Probably involves a dead body and a pie...
Dave
Thanks for the good suggestions. I do have a question though.
> Slide 8: "The plume is only projected to be ~ 5 -10" highand ~17" wide
> at final detectable extent (dims as it grows)"
> The values you quote above are for a max scenario cloud. I would talk
> about both clouds, including the 95% certainty cloud mentioned in
> Chase Miller's computations.
What are the values for the 95% certainty cloud? I'm not finding
> about both clouds, including the 95% certainty cloud mentioned in
> Chase Miller's computations.
those.
> Once you have finalized the presentation (or maybe after you have
> presented it and can tweak it based on audience questions), please
> post a link to the final back here with GNU permission for other clubs
> to reuse it.
> P.S. - I like the Three Stooges picture on Slide 12.
at on the floor. Probably involves a dead body and a pie...
Dave
cano...@yahoo.com
Sep 10, 2009, 3:44:47 AM9/10/09
to LCROSS_Observation
On Sep 9, 8:59 am, dave_dockery <dadock...@gmail.com> wrote:
> What are the values for the 95% certainty cloud? I'm not finding
> those.
That's the one that the Chase Miller quote describes up thread. 9.6
> What are the values for the 95% certainty cloud? I'm not finding
> those.
arcseconds by 1.7 arcseconds. Happy presenting. - Kurt
dave_dockery
Sep 11, 2009, 3:12:50 PM9/11/09
to LCROSS_Observation
Hi Jim,
Thanks very much for the feedback and sorry it took a while to reply.
You bring up some interesting points on plume brightness uncertainty
but in the interest of keep the talk short and at a fairly high level
I intend to just point out that there's a good deal of uncertainty to
the projections and go with the numbers from the NASA Citizen Science
Portal for now.
The image of Saturn being occulted by the moon was one I took back in
spring 2000? using a webcam and is presented purely to show how lunar
features will sometimes be saturated at the correct exposure level for
a much dimmer object.
I have to give the talk tomorrow morning so I'll be scrambling tonight
to digest the new info released today and make some updates.
Dave
> > Las Cruces, NM.http://home.comcast.net/~dave.dockery/- Hide quoted text -
>
> - Show quoted text -
Thanks very much for the feedback and sorry it took a while to reply.
You bring up some interesting points on plume brightness uncertainty
but in the interest of keep the talk short and at a fairly high level
I intend to just point out that there's a good deal of uncertainty to
the projections and go with the numbers from the NASA Citizen Science
Portal for now.
The image of Saturn being occulted by the moon was one I took back in
spring 2000? using a webcam and is presented purely to show how lunar
features will sometimes be saturated at the correct exposure level for
a much dimmer object.
I have to give the talk tomorrow morning so I'll be scrambling tonight
to digest the new info released today and make some updates.
Dave
>
> - Show quoted text -
Paul Mortfield
Sep 12, 2009, 9:18:10 AM9/12/09
to lcross_ob...@googlegroups.com
Good luck with the talk Dave.
Let us know how it turns out and if you'd like to post the finished talk in
the files section.
cheers,
...paul.
Let us know how it turns out and if you'd like to post the finished talk in
the files section.
cheers,
...paul.
----- Original Message -----
From: "dave_dockery" <dado...@gmail.com>
To: "LCROSS_Observation" <lcross_ob...@googlegroups.com>
Sent: Friday, September 11, 2009 15:12
Subject: [LCROSS_OBS: 1057] Re: LCROSS Imaging Presentation for Review
Hi Jim,
Thanks very much for the feedback and sorry it took a while to reply.
You bring up some interesting points on plume brightness uncertainty
but in the interest of keep the talk short and at a fairly high level
I intend to just point out that there's a good deal of uncertainty to
the projections and go with the numbers from the NASA Citizen Science
Portal for now.
The image of Saturn being occulted by the moon was one I took back in
spring 2000? using a webcam and is presented purely to show how lunar
features will sometimes be saturated at the correct exposure level for
a much dimmer object.
I have to give the talk tomorrow morning so I'll be scrambling tonight
to digest the new info released today and make some updates.
Dave
On Sep 9, 6:05 pm, Jim Mosher <jimmos...@gmail.com> wrote:
From: "dave_dockery" <dado...@gmail.com>
To: "LCROSS_Observation" <lcross_ob...@googlegroups.com>
Sent: Friday, September 11, 2009 15:12
Subject: [LCROSS_OBS: 1057] Re: LCROSS Imaging Presentation for Review
Hi Jim,
Thanks very much for the feedback and sorry it took a while to reply.
You bring up some interesting points on plume brightness uncertainty
but in the interest of keep the talk short and at a fairly high level
I intend to just point out that there's a good deal of uncertainty to
the projections and go with the numbers from the NASA Citizen Science
Portal for now.
The image of Saturn being occulted by the moon was one I took back in
spring 2000? using a webcam and is presented purely to show how lunar
features will sometimes be saturated at the correct exposure level for
a much dimmer object.
I have to give the talk tomorrow morning so I'll be scrambling tonight
to digest the new info released today and make some updates.
Dave
On Sep 9, 6:05 pm, Jim Mosher <jimmos...@gmail.com> wrote:
cano...@yahoo.com
Sep 12, 2009, 8:43:11 PM9/12/09
to LCROSS_Observation
Thanks for posting the update to the Files section. - Kurt
On Sep 11, 1:12 pm, dave_dockery <dadock...@gmail.com> wrote:
<snip> I have to give the talk tomorrow morning so I'll be scrambling
tonight
> to digest the new info released today and make some updates.<snip>
> Dave
On Sep 11, 1:12 pm, dave_dockery <dadock...@gmail.com> wrote:
<snip> I have to give the talk tomorrow morning so I'll be scrambling
tonight
> to digest the new info released today and make some updates.<snip>
> Dave
dave_dockery
Sep 12, 2009, 6:52:41 PM9/12/09
to LCROSS_Observation
Thanks Paul.
The talk went well today and it turns out I'm giving it again to the
Astronomical Society of Las Cruces in two weeks. I included info on
where I think the actual impact point will be based on the "sweet
spot" image released in the target selection briefing and hope I
located it correctly on the NMSU finder map. (I'm sure Chas will
update us soon). I have to admit I'm still somewhat confused by
conflicting predictions of plume brightness and may need to update
this again for the ASLC talk after the dust settles (pun intended.)
I've posted the updated version in the files section. See: "Imaging
the LCROSS Impact Event 9_12.pdf" or follow the link below to my
website.
The feedback I received here was very helpful and I hope people find
the information useful. Feel free to use the presentation to share
information on this event.
Thanks,
On Sep 12, 7:18 am, "Paul Mortfield" <P...@BackyardAstronomer.com>
wrote:
> > > Las Cruces, NM.http://home.comcast.net/~dave.dockery/-Hide quoted
> > > text -
>
> > - Show quoted text -- Hide quoted text -
The talk went well today and it turns out I'm giving it again to the
Astronomical Society of Las Cruces in two weeks. I included info on
where I think the actual impact point will be based on the "sweet
spot" image released in the target selection briefing and hope I
located it correctly on the NMSU finder map. (I'm sure Chas will
update us soon). I have to admit I'm still somewhat confused by
conflicting predictions of plume brightness and may need to update
this again for the ASLC talk after the dust settles (pun intended.)
I've posted the updated version in the files section. See: "Imaging
the LCROSS Impact Event 9_12.pdf" or follow the link below to my
website.
The feedback I received here was very helpful and I hope people find
the information useful. Feel free to use the presentation to share
information on this event.
Thanks,
Dave
Dave Dockery
Las Cruces, NM
http://home.comcast.net/~dave.dockery/
Dave Dockery
Las Cruces, NM
On Sep 12, 7:18 am, "Paul Mortfield" <P...@BackyardAstronomer.com>
wrote:
> > > text -
>
> > - Show quoted text -- Hide quoted text -
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