could you see stars if you were standing on the moon?

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could you see stars if you were standing on the moon?

Postby tibbert » Sat Sep 18, 2010 12:23 am

Sorry if this is really obvious and/or been asked too many times but........ Is it possible to see the stars whilst standing on the illuminated surface of the moon?....I thought as we are looking at sunlight bouncing off it that it must be daytime on the surface and too bright to see the much dimmer stars? Would it mean you cant see any stars at all unless you were in a position that was shaded from the sun, on the moon and within the solar system like the inner planets? I also wondered if there had been any missions that had crossed the terminator or to the far side at all?
Any clues would be great! cheers!
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RE: could you see stars if you were standing on the moon?

Postby brianb » Sat Sep 18, 2010 9:33 am

The Apollo astronauts reported being able to see the brighter stars if they stood in the shadow of the LM and raised the protective visor. The visor, which was gold in appearance, was required when they were in sunlight to protect their eyes from the dangerous level of ultra violet radiation which reaches the Moon's surface because of the lack of atmosphere.

The stars do not appear in images taken by the astronauts because the exposures were set for the sunlit landscape.

The Apollo spacecraft relied on visual judgement for landing guidance and were therefore unable to land on the night side of the moon - in fact there was a requirement for the altitude of the sun at the time of landing, IIRC it was within a few degrees of 15 degrees altitude, reasonably high for illumination but low enough for significant obstacles to cast obvious shadows. Landings on the far side of the moon were also ruled out for lack of communication with ground based Mission Control, and landings at high lunar latitudes were impossible because of the greater energy budget required to insert spacecraft into highly inclined orbits & return to earth afterwards.

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RE: could you see stars if you were standing on the moon?

Postby lancashire astroguy » Sat Sep 18, 2010 3:06 pm

[quote]ORIGINAL: Tibbert

I also wondered if there had been any missions that had crossed the terminator or to the far side at all?

[/quote]

None of the landings occurred on either the night-time side or the far side. However, a few lucky astronauts got the chance to fly above both. The command module pilots remained alone in lunar orbit whilst their colleagues flew down to the Moon below. If they got the chance to dim the lights in the command module whilst flying over the night side, they would have been treated to a fantastic view of the stars through the porthole window. Without an atmosphere, stars visible to magnitude +7 or fainter become visible. The most distant object visible to the eye is no longer the Andromeda galaxy but M81 in Ursa Major - 12 million light years away! A small compensation, perhaps, for not actually walking on the Moon.

Of course, if the visionless US president Obama had not cancelled the Orion project, then many more astronauts might have seen the stars from the Moon [:@]. The ultimate aim of Orion was to build a permanent base on the Moon, most likely in one of the permanently shadowed ice-trap craters at the South Pole. I guess this will not happen in our lifetimes now. [:o]

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RE: could you see stars if you were standing on the moon?

Postby tibbert » Sat Sep 18, 2010 4:30 pm

cheers for your comments!!
I saw on the nasa site they said if the astronauts shaded their eyes from the sun on the surface, they were able to see stars...but the surface is reflective and would have reflected back up at them aswell as directly downwards from the source. If I were to stand in a well shaded area on earth i couldnt see stars above, is that just because of light bouncing around our atmosphere??

cheers guys!!
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RE: could you see stars if you were standing on the moon?

Postby brianb » Sat Sep 18, 2010 5:36 pm

[quote]If I were to stand in a well shaded area on earth i couldnt see stars above[/quote]
Actually if you look through a very long tube pointed in the right direction you [i]might[/i] be able to see stars even in full daylight from the surface of Earth. Such observations have been reported.

In very clear air at high altitude the brightest stars appear at about the same time the sun sets.

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RE: could you see stars if you were standing on the moon?

Postby arthur dent » Sat Sep 18, 2010 8:56 pm

[quote]ORIGINAL: Tibbert
If I were to stand in a well shaded area on earth i couldnt see stars above, is that just because of light bouncing around our atmosphere??
[/quote]
Yes, that is correct.

I believe, though I haven't witnessed it myself (although this may well prompt me to try) that by using a telescope you can indeed see the brightest stars during dalight - much like you can see Venus or Mercury in the twilight morning or evening sky.

Our atmosphere scatters an awful lot of light - which is why the sky appears blue during the day and redder in the mornings and evenings when sunlight passes through thicker layers of atmosphere.

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RE: could you see stars if you were standing on the moon?

Postby tibbert » Sat Sep 18, 2010 11:26 pm

i can understand that when the sun is at a low angle there is sufficient darkness to see some of the brighter stars, as in early morning or evening.. but not say, from the bottom of a ravine in the shade.

i guess my question ought to be:Can you only see light photons head on? and would you, in vacuum, or very small atmosphere, standing in the shade of a crater or large rock be able to see through them and view the stars behind it?
the closer to the terminator you go, it becomes, as you say, the morning?evening time when you can see the brighter stars... but not stars in general?

i've seen programs where they go up in a u2 spy plane. they were only 70,000 ft up but.. the sky above only looked a dark navy colour. no real reference to me the viewer. cannae trust cameras.. but they didnt say they could see stars.
i'm gonna check around and see if i can find any pics taken by the space station or any shuttle mission, of stars.. hmmmm??

cheers again for comments!
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RE: could you see stars if you were standing on the moon?

Postby philip pugh » Sun Sep 19, 2010 12:50 am


[quote]ORIGINAL: brianb

[quote]If I were to stand in a well shaded area on earth i couldnt see stars above[/quote]
Actually if you look through a very long tube pointed in the right direction you [i]might[/i] be able to see stars even in full daylight from the surface of Earth. Such observations have been reported.

In very clear air at high altitude the brightest stars appear at about the same time the sun sets.


[/quote]

My best "pot" in daylight (without optical aid) was Jupiter, then at mag -2.5 but I knew it was close to the Moon and where to look. I've seen Venus in full daylight many times and shown it to non astronomers. I've heard of people seeing bright stars in daylight and the limit seems to be about mag 0.
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RE: could you see stars if you were standing on the moon?

Postby lancashire astroguy » Sun Sep 19, 2010 1:40 am


[quote]ORIGINAL: Tibbert

i've seen programs where they go up in a u2 spy plane. they were only 70,000 ft up but.. the sky above only looked a dark navy colour. no real reference to me the viewer. cannae trust cameras.. but they didnt say they could see stars.

[/quote]

As I understand it, a significant number of stars starts to become visible at altitudes of around 30km (100,000ft). I guess the reason you don't see stars in photo's or video's taken at that attitude is the same reason as why you don't see stars on the Apollo Moon landing pictures. The camera exposure time must be low enough for the bright forground to remain correctly exposed. By contrast, stars need a higher exposure time.

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RE: could you see stars if you were standing on the moon?

Postby worcspaul » Sun Sep 19, 2010 10:16 am

The same applies to the human eye. The brightness of the lunar surface would cause an astronaut's pupils to contract to cut down the light reaching the retina . This would thus affect the ability to see stars unless the eyes were shielded from the brightness of the surface. If they [u]were[/u] shielded, the astronaut's pupils would gradually dilate, letting in more starlight, as ours do when we become dark-adapted. The moment a stronger light source (lunar surface or, in our case, a bedroom light/torch/car headlamp) is introduced the pupils immediately contract to protect the retina, preventing the astronaut/us from seeing stars that we could see moments before.
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