Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Feb 9, 2010 12:56:31 GMT -4
I don't have the figures handy but I do know that the distance from the Earth to the Moon is less than the distance the Earth travels in one day. Earth travels about 30 km/s in its orbit around the Sun; therefore, it crosses the diameter of the Moon's orbit in a little over 7 hours.
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Post by tedward on Feb 9, 2010 14:24:05 GMT -4
Still bemused as to the hanging on to this topic by the usual suspects anyway.
I see Mr White is back with a few and knickers in a twist over reflecting lasers in the video I looked at.
Edit. Trying to use proper grammar like wot I was tort in skool.
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Post by laurel on Feb 9, 2010 14:37:12 GMT -4
Likewise, it should also be possible to see stars on the Moon provided your eyes are shielding from light and you give your eyes some time to dark adapt. I believe Cernan said he could see some stars while he was in the shadow of the LM, where the LM helped to shade his eyes from the glare of the bright sunlit lunar surface. Under most conditions, no stars would be visible because the bright surface dominates the view and overwhelms the faint stars. From the ALSJ at approximately 113:19:58 on the linked page: [Schmitt - "We couldn't see the stars out the window or when we were out on the surface. It took the collimation of the telescope to eliminate all of the reflected light reaching your eye from your surroundings. Even in the LM shadow, there were too many bright things in your field-of-view for the stars to be visible."]
[Cernan - "When you were in the lunar module, looking out the window, you certainly couldn't see stars. Using the telescope was sort of like being in a deep well; it cut out all the reflected light and let you see the stars. It was also generally true that, when you were on the surface in the LM's shadow, there were too many bright things in your field-of-view for the stars to be visible. But I remember that I wanted to see whether I could see stars, and there were times out on the surface when I found that, if you allowed yourself to just focus and maybe even just shielded your eyes to some degree, even outside the LM shadow you could see stars in the sky. And, quite frankly, under the right conditions here on Earth on a bright sunlit day, you can do the same thing. I could see stars through my helmet visor; not easily, but it can be done."]history.nasa.gov/alsj/a17/a17.postland.html
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Post by seemoe on Feb 9, 2010 22:15:00 GMT -4
Apparently he thinks the sunlight on the moon somehow doesn't affect the development of a photograph like it does on Earth
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Feb 10, 2010 1:40:44 GMT -4
The 30 seconds applies to both the Moon and Earth. You just have to take your star photos at night if you're on Earth. You can do it either night or day on the Moon as long as you take precautions previously discussed.
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Post by theteacher on Feb 10, 2010 10:56:11 GMT -4
Likewise, it should also be possible to see stars on the Moon provided your eyes are shielding from light and you give your eyes some time to dark adapt. I believe Cernan said he could see some stars while he was in the shadow of the LM, where the LM helped to shade his eyes from the glare of the bright sunlit lunar surface. Under most conditions, no stars would be visible because the bright surface dominates the view and overwhelms the faint stars. From the ALSJ at approximately 113:19:58 on the linked page: [Schmitt - "We couldn't see the stars out the window or when we were out on the surface. It took the collimation of the telescope to eliminate all of the reflected light reaching your eye from your surroundings. Even in the LM shadow, there were too many bright things in your field-of-view for the stars to be visible."]
[Cernan - "When you were in the lunar module, looking out the window, you certainly couldn't see stars. Using the telescope was sort of like being in a deep well; it cut out all the reflected light and let you see the stars. It was also generally true that, when you were on the surface in the LM's shadow, there were too many bright things in your field-of-view for the stars to be visible. But I remember that I wanted to see whether I could see stars, and there were times out on the surface when I found that, if you allowed yourself to just focus and maybe even just shielded your eyes to some degree, even outside the LM shadow you could see stars in the sky. And, quite frankly, under the right conditions here on Earth on a bright sunlit day, you can do the same thing. I could see stars through my helmet visor; not easily, but it can be done."]history.nasa.gov/alsj/a17/a17.postland.htmlIt seems to me, that Cernan asserts a mere assumption here. Is it possible to see stars on a bright sunlit day - even under the right conditions?
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Post by echnaton on Feb 10, 2010 11:11:40 GMT -4
It seems to me, that Cernan asserts a mere assumption here. Is it possible to see stars on a bright sunlit day - even under the right conditions? I've seen Jupiter by eye when the sun was still up and in a brighter sky than I ever thought possible. It took some help by using binoculars to locate it then letting my vision go out of focus to make it appear. I doubt that stars can be seen before dusk.
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Post by Grand Lunar on Feb 11, 2010 16:26:48 GMT -4
If you can block all light sources from your eyes, including secondary light sources, you probably could see stars.
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Post by theteacher on Feb 11, 2010 17:31:54 GMT -4
If you can block all light sources from your eyes, including secondary light sources, you probably could see stars. Well, one more - maybe - assumption :-) Does anyone know if it is a verifiable fact? Now I'm getting curious!
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Post by trebor on Feb 11, 2010 19:14:11 GMT -4
If you can block all light sources from your eyes, including secondary light sources, you probably could see stars. The main snag here is that one of those light sources is the sky.
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Post by Grand Lunar on Feb 18, 2010 9:54:27 GMT -4
If you can block all light sources from your eyes, including secondary light sources, you probably could see stars. The main snag here is that one of those light sources is the sky. I thought the person was referring to the lunar sky. Shame on me!
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Post by Grand Lunar on Feb 18, 2010 9:58:25 GMT -4
Not sure if this belongs here....
The subject of the LM sitting with one side in the sun and one side in darkness was brought up. I did mention the info from Clavius concerning this. Then I was asked "Why then did the CM (obviously referring to the CSM) need to perform the barbeque roll?"
I assumed this was because it didn't have he same thermal covering as the LM.
But I wish to be certain; what made the difference between the CSM to require a PTC roll where the LM didn't?
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Post by PeterB on Feb 18, 2010 10:05:44 GMT -4
But I wish to be certain; what made the difference between the CSM to require a PTC roll where the LM didn't? I believe it was to ensure the heatshield and various subsystems like fuel lines didn't get too cold, as they would on a permanently shaded side of a spacecraft.
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Post by Grand Lunar on Feb 18, 2010 10:08:47 GMT -4
Makes sense, since the LM didn't have a heat shield, nor was it's propulsion system (except for the ascent stage) expected to be used again. Didn't the electronics provide heat?
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Post by echnaton on Feb 18, 2010 10:51:02 GMT -4
The LM only had to survive for three days without changing it orientation to the sun, whereas the CSM had to last two weeks. The electronics on the assent stage that were outside of the crew compartment were attached to a cold plate that absorbed the heat and kept them at safe operating temperatures.
From what I have read, the roll program was a reasonable precaution to a hypothesized but potentially real and fatal problem. Nobody really new how the equipment and heat shield would be affected by the extreme differences in solar exposure so they took a conservative and low budget approach. You have pilots that are accustomed to being concerned about craft safety so let them fly the ship.
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