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  Mercury - Gemini - Apollo
  Earth photos taken on the lunar surface

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Author Topic:   Earth photos taken on the lunar surface
LM-12
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Posts: 1174
From: Ontario, Canada
Registered: Oct 2010

posted 08-18-2014 09:58 PM     Click Here to See the Profile for LM-12     Edit/Delete Message   Reply w/Quote
Apollo 11 frame 5924 and Apollo 17 frame 20463 are two Earth photos taken during EVA activities. You can tell by looking at the Earth terminator that the two landing sites are at different latitudes.

I do not see the Reseau numbers on some of the Earth photos that Gene Cernan took. Perhaps it was an awkward angle, so I suspect that Cernan may have held his camera upside down or sideways to take those shots, including:
  • frames 20957 to 20961 at Station 2
  • frames 20465 and 20466 at the flag

Headshot
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Posts: 352
From: Streamwood, IL USA
Registered: Feb 2012

posted 08-19-2014 06:57 AM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
I believe that the latitude of a lunar landing site can be roughly determined by the altitude of the Earth above the lunar horizon, e.g. the Earth would be on the horizon at the Moon's poles and be almost overhead when viewed from the lunar equator.

I am not certain that the Earth's terminator has any bearing on the latitude of a lunar landing site, although it might be used to determine the difference in longitude between two different landing site.

Someone help us out with this.

schnappsicle
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Posts: 180
From: Houston, TX, USA
Registered: Jan 2012

posted 08-19-2014 07:16 AM     Click Here to See the Profile for schnappsicle   Click Here to Email schnappsicle     Edit/Delete Message   Reply w/Quote
You are correct on both counts. The earth goes through phases just like the moon does when viewed from earth, but unlike the moon, the earth stays roughly in the same spot in lunar sky at all times.

LM-12
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From: Ontario, Canada
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posted 08-19-2014 08:33 AM     Click Here to See the Profile for LM-12     Edit/Delete Message   Reply w/Quote
Using Apollo 17 frame 20961 as an example:

It would seem to me that (hypothetically) if someone was standing on the lunar equator when Cernan took that photo, they would see a horizontal Earth terminator. And someone standing on the lunar north or south pole would see a vertical Earth terminator.

Is that correct?

One Big Monkey
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From: West Yorkshire, UK
Registered: Jul 2012

posted 08-19-2014 09:28 AM     Click Here to See the Profile for One Big Monkey     Edit/Delete Message   Reply w/Quote
This superb analysis takes the idea a step further!

Headshot
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Posts: 352
From: Streamwood, IL USA
Registered: Feb 2012

posted 08-19-2014 09:45 AM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
Yes LM-12, your reasoning is correct also. The angle of the Earth's terminator would vary by latitude as well.

It is best to measure the angle of the terminator during half-Earth, when the terminator is a straight line. Despite what that excellent video shows, when the Earth is gibbous there is some subjectivity to determining the terminator angle.

Glint
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From: New Windsor, Maryland USA
Registered: Jan 2004

posted 08-19-2014 01:30 PM     Click Here to See the Profile for Glint   Click Here to Email Glint     Edit/Delete Message   Reply w/Quote
The angle of the terminator primarily varies by season. The seasons are caused by the earth's axial tilt.

LM-12
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From: Ontario, Canada
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posted 08-19-2014 02:47 PM     Click Here to See the Profile for LM-12     Edit/Delete Message   Reply w/Quote
Frame 9189 is a LM and Earth view from the lunar surface on Apollo 14.

None of the Apollo 15 and Apollo 16 Hasselblad photos taken on the lunar surface seem to show the Earth. That is a surprise. Can you find any?

LM-12
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Posts: 1174
From: Ontario, Canada
Registered: Oct 2010

posted 08-21-2014 12:50 PM     Click Here to See the Profile for LM-12     Edit/Delete Message   Reply w/Quote
I take it from the "superb" Earthrise video that One Big Monkey posted above that (1) the angle of the Earth's axis relative to the lunar horizon changes with latitude and can be used to determine lunar latitude, and (2) the elevation of the Earth above the lunar horizon changes with longitude and can be used to determine lunar longitude.

So, if one can do all the calculations, the (approximate) location where an Earth photo like 20961 was taken can be determined from the photo alone? Amazing.

All times are CT (US)

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