The following examples show how LTVT can be used to provide a quick interpretation of the information that has been released about possible LCROSS impact dates, times and locations. Early anecdotal evidence suggested that the impact might occur at some unspecified time on October 8, 2009. A later announcement mentioned possible impacts on October 8 at 10:30 UT, October 9 at 11:30 UT, October 10 at 12:30 UT or October 11 at 13:30 UT, corresponding to launches on June 17, 18, 19 or 20, 2009. Since then, the spacecraft carrying LCROSS successfully lifted off at 5:32:00.1 pm EDT on June 18th; and the LCROSS home page at NASA/Ames currently projects an impact near the Moon's south pole at 11:31:19 UT on October 9th. Still more recently, an exact target location was announced, and changed.

Viewing Geometry

(click on the thumbnails to see full-sized LTVT screenshots)

Regions from which Moon can be seen

The LTVT Earth viewer can be used to visualize the regions of the Earth from which the Moon can be viewed at the announced impact hours. In the Earth Viewer displays, the Moon is visible only from the hemisphere shown, and part of it may be in daylight (as in the Moon displays, the hemisphere bordered by the red line is in sunlight, and that bordered by the blue line is in darkness).

Oct 8 -- 10:30 UT
Oct 9 -- 11:30 UT
Oct 10 -- 12:30 UT
Oct 11 -- 13:30 UT
external image LCROSS_2009Oct8_1030UT_EarthView.JPG?size=64
external image LCROSS_2009Oct9_1130UT_EarthView.JPG?size=64
external image LCROSS_2009Oct10_1230UT_EarthView.JPG?size=64
external image LCROSS_2009Oct11_1330UT_EarthView.JPG?size=64

How Moon will look

The following LTVT simulations at 10X zoom approximate the appearance of the Moon's south pole as seen from Hawaii at the stated dates and times. They were obtained by entering this information and asking LTVT to "Compute Geometry". They were painted using Earth-based images taken with similar lighting conditions, remapped to the expected librations. They are shown south up.

Note: these simulations were prepared many months in advance. The official count-down clock now predicts an impact time of 11:31:19 UT (07:31:19 am EDT / 04:31:19 am PDT) on October 9th. The impact plume, if visible from Earth should appear by 11:32 UT, and last for perhaps a couple of minutes more.

Oct 8 -- 10:30 UT
Oct 9 -- 11:30 UT
Oct 10 -- 12:30 UT
Oct 11 -- 13:30 UT
external image LCROSS_2009Oct8_1030UT.JPG?size=64
external image LCROSS_2009Oct9_1130UT.JPG?size=64
external image LCROSS_2009Oct10_1230UT.JPG?size=64
external image LCROSS_2009Oct11_1330UT.JPG?size=64
external image LCROSS_2009Oct8_1030UT_labeled.JPG?size=64
external image LCROSS_2009Oct9_1130UT_labeled.JPG?size=64
external image LCROSS_2009Oct10_1230UT_labeled.JPG?size=64
external image LCROSS_2009Oct11_1330UT_labeled.JPG?size=64
Marc Patry
Mario Weigand
Stefan Lammel
Oscar Canales Moreno

The final image has been positioned to show more of the features on the visible disk, including Clavius at the bottom right.

Estimated dates and times of source images (times marked with a * have been guessed based on the appearance of the photo):

Time (UT)
Marc Patry
2008 Oct 19
Mario Weigand
2008 Oct 20
Stefan Lammel
2006 Oct 14
Oscar Canales Moreno
2007 Nov 03

The Target Site

Details of the target site (in the crater Cabeus) and NASA computer simulations of the view expected from Earth can be found on the LCROSS Citizen Science page, particularly in the presentation uploaded by LCROSS Principal Investigator Tony Colaprete. More detailed simulations showing the expected size and location of the ejecta plume as a function of time as seen from overhead by the shepherding spacecraft can be found in a separate file.

The Mario Weigand image, as shown above remapped to the October 9th geometry, is probably the most accurate prediction of what the Moon will look like from Earth at impact. The NASA simulations, apparently based on LRO altimeter data, are remarkably realistic, but show some areas as being in sunlight that were not observed in sunlight in Mario's photograph. Because the Sun's longitude and latitude at the time of Mario's observation were very close to the impact values, these discrepancies are presumably shortcomings of the simulations.

Here are more detailed LTVT simulations of how the Moon will appear at impact from Jim Mosher's home in Newport Beach, California based on Mario's image taken with nearly identical lighting and libration in latitude (click for enlargements):

external image 2009_Oct_09_equatorial_view.JPG?size=64
external image 2009_Oct_09_mirror_reversed_alt-az_view.JPG?size=64

The image on the left is a classic(?) north-up view through an equatorially mounted telescope. The one on the right is shows the mirror-reversed view through the star diagonal of a altitude-azimuth ("Dobsonian") mounted telescope. The first should be roughly applicable over a wide geographic area; the Moon's rotation angle in the latter configuration is quite dependent on location.

These views have been labeled with the unofficial names given by Ewen Whitaker to three prominent south polar peaks ("M1", "M4" and "M5"). According to Tony Colaprete's simulations, the impact location and the first ejecta to reach sunlight will be hidden by M1. As indicated in the LTVT screenshots, M1 can be easily located based on its position radially inward from the prominent limb peak M5 (whose identity can be verified by its relation to the somewhat smaller M4). As indicated by the long arrow, the impact point will be hidden by the flank of M1 on the side closest to M4.

What is seen as a shadow at the base of M1 is actually a shadow cast on the floor of Cabeus by unrelated parts of the crater limb. Sunlight in the impact area is streaming roughly parallel to the Moon's limb and the shadow cast by M1 itself is seen as a completely separate and initially thin band of shadow (mostly hidden by topography) extending out of M1 on the opposite side and terminating in an unnamed crater well to the right of M1 (in the equatorial view).

Additional tips for finding the impact site, some using Mario's image apparently uncorrected for the difference in longitudinal libration, can be on the LCROSS project page, and on the LCROSS Google Groups page.

This page has been edited 22 times. The last modification was made by - JimMosher JimMosher on Oct 8, 2009 1:52 pm