[LCROSS] Illumination during impact target phases

[cano...@yahoo.com]

The NASA LCROSS Image Specifications Press Release states that "[t]he
LCROSS mission plans to impact the moon when the lunar phase is
approximately between 76 degrees and 150 degrees and between 210 and
284 degrees."

The LCROSS impact target phases correspond approximately to the
following terminator positions and lunar days:

Phase | Lunar Day | Terminator longitude | Terminator Type | Quarter

76 to | 6.2 | E14 | Rising | First
150 | 12.3 | W60 | Rising | Second

and

210 to | 17.2 | E60 | Setting | Third
284 | 23.3 | W14 | Setting | Fourth

- Kurt

[Derek C Breit]

and

- Kurt

How does this relate to percent illuminated ?

Derek

[cano...@yahoo.com]

On Feb 8, 10:01 am, "Derek C Breit" <breit_id...@hotmail.com> wrote:
<snip all> > How does this relate to percent illuminated ? - Derek

To correct a prior removed post and to answer your narrow question:

The NASA LCROSS Image Specifications Press Release states that "[t]he
LCROSS mission plans to impact the moon when the lunar phase is
approximately between 76 degrees and 150 degrees and between 210 and

284 degrees." A more precise term than lunar phase in this context is
the lunar age - which is expressed as a number of degrees between 0
and 360 degrees.

The LCROSS impact target lunar ages correspond approximately to the
following terminator positions, lunar days and illuminated fractions:

Age | Lunar Day | Terminator longitude | Terminator Type | Quarter |
Illuminated Fraction

76 to | 6.2 | E14 | Rising | First | 38%
150 | 12.3 | W60 | Rising | Second | 93%
and
210 to | 17.2 | E60 | Setting | Third | 93%
284 | 23.3 | W14 | Setting | Fourth | 38%

Illuminated fraction is related to the age of the Moon, expressed in
degrees D, by the formula:
Illuminated fraction = [ 1/2(1 - cos(degs2rads(D)) ] * 100

You may want to consider the above with respect to your exposure
calibration question.

Three simulated images at the limits of the age and illuminated
fraction percent are provided here:

5-29-2009 Northern region libration +3 illuminated fraction 38% - 1st
Qtr
http://lcross_observation.googlegroups.com/web/20090529_38IF_3Lib1stQtrSimulated.jpg

3-12-2009 Northern region libration +6.2 illuminated fraction 93% -
Third Qtr
http://lcross_observation.googlegroups.com/web/20090312_93IF6_2Lib3rdQtrSimulated.jpg

7-27-2009 Northern region libration +7.0 illuminated fraction 38% -
1st Qtr
http://lcross_observation.googlegroups.com/web/20090727_38IF_7Lib1stQtrSimulated.jpg

These illuminated fraction range endpoints are more favorable for
imaging, since the backscatter and glare of the Moon's bright limb is
less near candidate impact points. But, there is nothing in the LCROSS
target age constraints that prohibit conducting the impact in the
middle of the range of illuminated fractions instead of at the more
favorable endspoints.

- Kurt

NASA LCROSS Image Specifications Press Release

http://www.nasa.gov/mission_pages/LCROSS/news/image_specifications.html