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infocusinc
2007-Sep-30, 07:21 PM
Phil,

In your Apollo FAQ you state the you would be able to see stars on the moon...

"On the Moon, the lack of air means that the sky is dark. Even when the Sun is high off the horizon during full day, the sky near it will be black. If you were standing on the Moon, you would indeed see stars, even during the day. "

What you don't state is that you would need to completely shield your eyes from the ambient light and then allow your eyes to dark adapt to do this.

DO you agree with my statement?

The next question it raises is how do you eliminate the the ambient light to allow your eyes to dark adapt?

Orion437
2007-Sep-30, 07:25 PM
"you would need to completely shield your eyes from the ambient light and then allow your eyes to dark adapt to do this."

What do you mean with this?

infocusinc
2007-Sep-30, 07:38 PM
"you would need to completely shield your eyes from the ambient light and then allow your eyes to dark adapt to do this."

What do you mean with this?

I mean you would need to block the ambient light from the lunar surface from entering your eyes so that your iris could open up enough to image the stars.

hhEb09'1
2007-Sep-30, 07:46 PM
The next question it raises is how do you eliminate the the ambient light to allow your eyes to dark adapt?Wouldn't it be sufficient to turn your back to the sun, and look up?

PS: naked eye, I can see Venus during the day. It's a magnitude -4, and very bright, but the biggest impediment to seeing seems to be the light of the blue sky. Without that, I'd bet I could see a lot higher magnitude.

infocusinc
2007-Sep-30, 07:51 PM
Wouldn't it be sufficient to turn your back to the sun, and look up?

PS: naked eye, I can see Venus during the day. It's a magnitude -4, and very bright, but the biggest impediment to seeing seems to be the light of the blue sky. Without that, I'd bet I could see a lot higher magnitude.

I don't think so but thats why I'm asking.

hhEb09'1
2007-Sep-30, 07:58 PM
I don't think so but thats why I'm asking.What ambient light would not be eliminated by doing that?

infocusinc
2007-Sep-30, 08:01 PM
What ambient light would not be eliminated by doing that?

There would still be light reflected from the surroundings, and still entering your eyes.

hhEb09'1
2007-Sep-30, 08:16 PM
There would still be light reflected from the surroundings, and still entering your eyes.But, that's why you look up. That would reduce that light by a considerable amount.

infocusinc
2007-Sep-30, 08:34 PM
But, that's why you look up. That would reduce that light by a considerable amount.

I understand...

But looking up would not eliminate the stray light entering your eyes. How much would be left and would you eyes still be able to open up enough to see stars?

R.A.F.
2007-Sep-30, 08:52 PM
Stand in the shade of a big rock, and don't look at the illuminated surface and you will see stars.

So what is the "conspiracy" here??

Grand_Lunar
2007-Sep-30, 09:06 PM
I think I know what Infocusinc refers to.

On YouTube, an HBer posted a video that shows footage from one of the Apollo missions. The camera pans the sky. The HBer claims that some stars, or at least Venus, should be visible.
The HBer also cites Phil's entry were he says that stars can be seen on the daytime side of the moon. The HBer uses this, and some ambiguous reference to NASA, as proof that people lie about not being able to see stars.
He also uses the same misquote that Bart Sibrel says about Armstrong saying in a debriefing about not being able to see stars (Jay talks about this on his website).

The idea that Infocusinc is looking for may be that for one to see stars on the lunar dayside, one would have to be in shadown, and face down sun and look away from the surface, allowing your eyes to be dark adapted.
Otherwise, the backscatter from the bright lunar surface would ruin your chances for seeing stars.

Trebuchet
2007-Sep-30, 09:28 PM
We also need to point out that there's a huge difference between seeing stars and photographing them. I can see them any clear night. (Not common around here lately!) But I'd have to take special pains to photograph them.

Grand_Lunar
2007-Sep-30, 09:47 PM
In the arguement that's given, it only refers to seeing the stars with the human eye.

KaiYeves
2007-Oct-01, 01:03 AM
In a comic, I explained it as there being too much light relected off the surface and the sky being too dark in comparison. I've tried to photograph stars without a special camera on Earth and they came out as junk. Do I need to re-write my comic?

Neverfly
2007-Oct-01, 03:51 AM
Grand Lunar caught on quickly I think. That was my first guess too.
Infocusinc is correct. It is not easy to see stars on the dayside of the moon due to the brightness of the sun. Even though there is no atmosphere, light is bouncing all over the place.

R.A.F pointed out that standing in a nice shadow should do the trick. Yes. Reducing the ambient light will help the eye see the stars.
Just looking upward would not be enough to see stars.

Taking a photograph that shows stars would require a very long exposure time and even if you saw the stars with your eyes, you would most likely not see them in a photo. Walk outside at night and snap a picture with your digi-cam of the sky. Tell me if the stars are visible at all.
ETA: to reduce nitpicking I'll clarify a bit.
Since there is no atmoshpere on the moon (essentially...) there is no air bouncing sunlight all over the place.
So yes it IS easier to view stars from the moon during the daytime. You need to block out what light you can. Light comes from:
the lunar surface
the sun
any light that may be reflecting from watery Earth
Light reflecting from your spacesuit or fellows or lander or rover or a tall rock

Svector
2007-Oct-01, 04:21 AM
But, that's why you look up. That would reduce that light by a considerable amount.

"Looking up" wasn't an easy thing for the astronauts to do, given the extremely restrictive nature of the suits and helmets they were wearing. Even if an astronaut were able to tilt his head back 90 degrees inside the suit (which he couldn't), the helmet itself had no mechanism by which to match his view angle.

Even if one were laying flat on his back looking straight into the void (as Charlie Duke probably was at one point), his periphery would still be filled with direct sunlight, and light reflecting off the bright terrain, LM, rover, miscellaneous equipment, and perhaps even the other astronaut.

The ability to see faint objects hinges in large part on a person's ability to eliminate excess light of this nature. Seeing stars within a restrictive space suit, peering through a darkened outer shield, in extremely bright, sunlit surroundings, would not have been the simple task most HBs would have people believe.



.

hhEb09'1
2007-Oct-01, 04:30 AM
But looking up would not eliminate the stray light entering your eyes. How much would be left and would you eyes still be able to open up enough to see stars?I'd say yes. BTW, here is a link to the BA's discussion about it (http://www.badastronomy.com/bad/tv/foxapollo.html#stars): "If you were standing on the Moon, you would indeed see stars, even during the day."

This wiki page (http://en.wikipedia.org/wiki/Pupil) says that the pupil can be enlarged to 8 mm in dim light. I think that is a little extreme, but let's use their figures. It says the pupil would be 3 or 4 mm in normal room light, 1.5 mm in bright light. So, even at the extremes, going from 8 down to 1.5, that is losing light gathering by 28 times. 8 mm has 28 times the light gathering of 1.5 mm. Still, that's less than four magnitudes. So, if you can see mag. six stars in dark earth skies, which is considered normal, you should be able to pick out even second magnitude stars on the surface of the moon, with no great effort at all.

I don't know what has actually been done.

peering through a darkened outer shield, That right there is probably the biggest factor!

I don't often go stargazing with sunglasses on. :)

PS: Here's a link to Clavius (http://www.clavius.org/stars.html): "Neil Armstrong reported not seeing any stars from the lunar surface, except through the navigation scopes (where the eyepiece screened out the other lights). Ed Mitchell reported seeing stars only when he specifically shut out extraneous light."

It doesn't sound like it was too hard to shut out the extraneous light.

Svector
2007-Oct-01, 05:28 AM
It doesn't sound like it was too hard to shut out the extraneous light.

It certainly wasn't impossible, but it took a good deal more effort than simply "looking up".

gwiz
2007-Oct-01, 08:44 AM
A big source of extraneous light would be reflections from the helmet and visor assembly. The suggestion of standing in the shadow of a big rock seems the best way to get the whole helmet into darkness.

Neverfly
2007-Oct-01, 08:53 AM
A big source of extraneous light would be reflections from the helmet and visor assembly. The suggestion of standing in the shadow of a big rock seems the best way to get the whole helmet into darkness.

Or stick your head in a crater but then you are looking in the wrong direction.

JayUtah
2007-Oct-01, 01:12 PM
Specifically, Mitchell stood in the shadow of the LM and waited for his eyes to dark-adjust.

The Apollo helmet restricts backward head tilting. It would be difficult to tilt your head back far enough to eliminate terrain from your field of view. And the inside of the LEVA is white; so it would reflect quite a bit of incidental light (say, from the ground or nearby machinery).

While it can be done, shutting out extraneous light requires a full-time effort. You can't casually do it while you're about other lunar surface activities.

hhEb09'1
2007-Oct-01, 01:26 PM
The next question it raises is how do you eliminate the the ambient light to allow your eyes to dark adapt?It looks like it's as simple as standing in a shadow, although I doubt that will get rid of all ambient light. I guess it gets rid of enough. What did the field of stars look like to Mitchell? Was it a couple stars, or a lot of stars?

Jay, what is the effect of the "darkened outer shield". Just how darkened are they?

SLF:JAQ SFDJS
2007-Oct-01, 02:35 PM
FYI - At the Standley Chasm is Australia there is a 20ft wide 500 ft deep cleft where one, standing at the bottom, can see stars in the daytime.

BertL
2007-Oct-01, 03:26 PM
FYI - At the Standley Chasm is Australia there is a 20ft wide 500 ft deep cleft where one, standing at the bottom, can see stars in the daytime.
I find that quite hard to believe because on earth you also have atmospheric distortion in daylight. No cleft can un-do atmospheric distortion.

JayUtah
2007-Oct-01, 04:15 PM
Jay, what is the effect of the "darkened outer shield". Just how darkened are they?

The outer visor attenuates visible light to about the same degree as a pair of mirror-finish sunglasses, such as those commonly used by skiers and mountaineers. I doubt one's ability to see stars through it even under otherwise ideal condition. The visor can be raised to allow seeing through the transparent visor and fishbowl layers. Those attenuate neglibly in the visible wavelengths.

JayUtah
2007-Oct-01, 04:33 PM
FYI - At the Standley Chasm is Australia there is a 20ft wide 500 ft deep cleft where one, standing at the bottom, can see stars in the daytime.

No, that's a myth. Read Phil's book.

The solid angle occupied by the restricted field of view provides just as much light scattered by the atmosphere as the same solid angle seen from an unrestricted viewpoint. While your eyes may adapt to the darkness at the bottom of a chasm (provided you don't look up), as soon as you look up you will light-adapt to the sky -- which is just as bright in that solid angle as it ever was and will form the basis for auto-calibration.

There is no ophthalmological process that allows the human eye to see both atmospheric daylight scatter and stars along the same view angle. The stars contribute too little light to make a sensible difference.

sts60
2007-Oct-01, 04:38 PM
I find that quite hard to believe because on earth you also have atmospheric distortion in daylight. No cleft can un-do atmospheric distortion.
Bert, the distortion is ~ the same day or night. The problem is scattered sunlight, which makes the day sky bright. I'm not sure I believe the claim; I don't think the stars are bright enough (except for that big yellow fella).

I have seen Venus in daylight with my unaided eyes. I just stood in the predawn twilight so that it was right by the corner of a roof, and used that as a reference point to pick it up after the Sun had risen.

hhEb09'1
2007-Oct-01, 05:12 PM
I have seen Venus in daylight with my unaided eyes. I just stood in the predawn twilight so that it was right by the corner of a roof, and used that as a reference point to pick it up after the Sun had risen.If you have a nice skymap, and a compass, you can pick it up anytime that the sky is clear. In order to show it to others though, you probably need to establish a corner like that, and position them so they can sight on it. I've done this at schools in the middle of the afternoon, with fifth graders.

nomuse
2007-Oct-01, 08:03 PM
For some reason I was unable to post to this earlier.

My mental model is this; as every backyard astronomer knows, you can't see the stars properly until you've dark-adapted. That doesn't go away just because you are on the Moon. And the daytime Moon is a heck of a lot brighter than the inside of a house or a car.

The other problem is, as other posters have pointed out, light doesn't hit one surface and stop. You are inside a white helmet, with lots of surfaces just waiting to catch any scattered light and throw it into your face. Add to that scratches or dust on the faceplate to scatter light. My mental model is; put on a motorcycle helmet with the visor down, have a friend put his hi-beams on, then stand in front of the car facing it. Now look upwards and try to see the stars.

Another thought, that comes later; the sky provides some useful calibration marks. Go out in late afternoon. Can you see the sun? Moon? How dark must it be before you can see Venus? How much longer before Jupiter, Sirius show up? Now the brightest stars?

As a reverse comparison, take a pencil flashlight out on your next star party. Turn it on suddenly when you are fully dark-adapted and marvel at that hot white beam. Now try it again while fumbling in the trunk at a service station. Now try it at the office. Now try it outside, under the sun. In the last case, it takes an effort just to see that the filament is glowing. No light seems to be coming out, none at all. Such is the difference in background illumination.

hhEb09'1
2007-Oct-01, 08:41 PM
Another thought, that comes later; the sky provides some useful calibration marks. Go out in late afternoon. Can you see the sun?Yes. :)
Moon?Yes.
How dark must it be before you can see Venus?Yes. :)

You can see Venus in broad daylight.

nomuse
2007-Oct-01, 08:52 PM
Yah...it's not that bright, tho. Basically, the idea is how much harder to have to work to see each object on the list. And I know, the jumps are hardly arranged in equal-sized steps!

But it almost startles me anew, each time I sit out around dusk, just how long I have to wait before it stops being "one to five" stars in the sky, to something resembling actual, say, constellations.

KaiYeves
2007-Oct-02, 12:13 AM
You can see Venus in broad daylight.
Although I usually see it after sunset or before sunrise.

endeavour
2007-Oct-02, 03:53 AM
FYI - At the Standley Chasm is Australia there is a 20ft wide 500 ft deep cleft where one, standing at the bottom, can see stars in the daytime.

As someone who has been to Standley Chasm on more than one occasion (and it's about 260 ft deep, not 500!) I can confirm that you do NOT see the stars when you are standing at the bottom in the daytime-just the glorious blue Central Australian sky :)

pzkpfw
2007-Oct-02, 04:26 AM
...Standley Chasm...myth...

I once read (or saw on T.V. - I don't actually remember) that well diggers could sometimes see the stars.

I guess that is also a myth - and I need to stop re-telling it.

(?)

Laguna
2007-Oct-02, 10:28 AM
I once read (or saw on T.V. - I don't actually remember) that well diggers could sometimes see the stars.

I guess that is also a myth - and I need to stop re-telling it.

(?)
You can see the stars from a deep well, but only the very brightest ones.
Not much more than about five or so, IIRC.
To see one of them it has to move directly over your well.
So a vast sky on or two stars on it and this little star has to move over your limited angle of view. Not very likely, but possible.

Obviousman
2007-Oct-02, 11:38 AM
FYI - At the Standley Chasm is Australia there is a 20ft wide 500 ft deep cleft where one, standing at the bottom, can see stars in the daytime.

I could go there and check during my Xmas leave, if interested. I have never been to the Alice before, so it might be fun.

Obviousman
2007-Oct-02, 11:40 AM
As someone who has been to Standley Chasm on more than one occasion (and it's about 260 ft deep, not 500!) I can confirm that you do NOT see the stars when you are standing at the bottom in the daytime-just the glorious blue Central Australian sky :)

Ooops! Disregard my last post then.

Grand_Lunar
2007-Oct-02, 12:28 PM
Although I usually see it after sunset or before sunrise.

A story.
Years ago, I noted Venus's position in the sky over several, cloud free days.
One day, a couple of hours before sunset, with the sky still blue, I looked in an area that I figured Venus was at. And behold! I saw it. It was very hard to make out, but I did see a tiny, pinpoint of light. It, of course, got progressivly brighter as dusk set in, confirming my observation.

I wonder if this is the sort of thing hoax believers will EVER take the time to do.

Laguna
2007-Oct-02, 12:34 PM
I wonder if this is the sort of thing hoax believers will EVER take the time to do.
Naahhhh,
They would have to leave the house and actually do some observing on their own.
We all know that THE TRUTHTM can only be found on some wacky Internet-Boards.

sts60
2007-Oct-02, 03:23 PM
Naahhhh,
They would have to leave the house and actually do some observing on their own.

There was a guy over on apollohoax who insisted that Neil Armstrong couldn't have covered up the Earth with his gloved thumb. After pages of calculations and even taking some pictures of my thumb held up next to the Moon, he actually, finally relented. (Only to flame out in a burst of profanity about five seven! dozen pages into another thread which started with him mentioning his "physics degree" from an unspecified college, and included the famous bit about the "searing radiation hell" which would have killed the astronauts.)

KaiYeves
2007-Oct-03, 01:45 AM
We all know that THE TRUTHTM can only be found on some wacky Internet-Boards.
Like this one.
No, wait- they can't handle the truth.

PhantomWolf
2007-Oct-04, 02:09 AM
You can see Venus in broad daylight.

I've seen it about 4pm, but the sky is a little darker then than at midday. I haven't looked for it during the middle of the day though, usually too busy.

KaiYeves
2007-Oct-04, 08:56 PM
I tried to take a photo of the Southern Cross when I was in Oz to show my mom. Unfortunately, my picture was completley dark, so the developing center threw it out. Will the HBer's claim that my trip to Australia never happened and I was in low Earth orbit the entire time?

PhantomWolf
2007-Oct-04, 09:20 PM
I tried to take a photo of the Southern Cross when I was in Oz to show my mom. Unfortunately, my picture was completley dark, so the developing center threw it out. Will the HBer's claim that my trip to Australia never happened and I was in low Earth orbit the entire time?

You have to use a long exposure time, this one was about 15 seconds:

http://lokishammer.dragon-rider.org/X/SouthCross2.jpg

KaiYeves
2007-Oct-04, 09:21 PM
You have to use a long exposure time, this one was about 15 seconds:
Oohps- forgot to mention that I was using a disposeable. I don't own a real camera.

PhantomWolf
2007-Oct-04, 09:37 PM
Well if you want, I'll take one for next time we have a nice clear night and you can claim it as yours. ;)

Swift
2007-Oct-04, 10:05 PM
I tried to take a photo of the Southern Cross when I was in Oz to show my mom. Unfortunately, my picture was completley dark, so the developing center threw it out. Will the HBer's claim that my trip to Australia never happened and I was in low Earth orbit the entire time?
Yes, your trip to Australia never happened. ;)

You came from another star and all you have is a disposable camera. Your people need to spend a little more on equipment. :p

hplasm
2007-Oct-05, 12:19 AM
Oohps- forgot to mention that I was using a disposeable. I don't own a real camera.

I got a half-decent (ie- you could see what it was... just) pic of an partial eclipse with a disposable camera in a sock.Yes.
Point and shoot was exactly right, but I did get a picture- about as good as if I had traced it with one of those tissue paper viewer boxes.... but a lot smaller. Yay for steam-powered science! :dance:

Grand_Lunar
2007-Oct-06, 01:35 AM
You have to use a long exposure time, this one was about 15 seconds:

http://lokishammer.dragon-rider.org/X/SouthCross2.jpg

Ha! I can make that with carbon paper and white paint! Hoax!


Seriously, a nice one. Do you think you can bring out the color of stars too? Or does that require stuff the pros use?

KaiYeves
2007-Oct-06, 01:58 AM
You came from another star and all you have is a disposable camera. Your people need to spend a little more on equipment.
I didn't buy fancy equipment as I would attract attention, or so I am told.

Obviousman
2007-Oct-06, 03:24 AM
Part of the problem is this particular HB is going back onto the old claim of "why did they not take any photographs of the stars from the lunar surface?".

I've tried to explain that the stars could be photographed from lunar orbit (which they did a small amount), and that the advantage of taking photos of the stars from the lunar surface is just not worth it.

You can take images of the stars from the Earth; you can't collect samples of the lunar soil, collect samples, etc, to the same degree from Earth. You need to take advantage of every second that you are there.

The CSM was more interested in mapping the lunar surface from orbit than taking photos of stars. The mission allowed detailed photography, something that you can't get from Earth. Yes you can launch an unmanned probe (e.g. Lunar Orbiter) but if you are in orbit already, waiting for the guys on the surface to finish, wouldn't it make sense to take full advantage of the lunar orbit for mapping?

Apparently the HBs think not; they should have been taking photos of the stars, or doing nothing on the lunar surface (tick tick tick tick...) waiting for their eyes to adjust so they can say "Gee, the stars are pretty!".

Of course they are, stupid! But what's the Moon like? How does the soil behave? Is there evidence of how it was formed? Are there elements that could be commercially or scientifically useful?

Apparently these questions do not get asked by HBs.

KaiYeves
2007-Oct-06, 01:14 PM
Apparently these questions do not get asked by HBs.
As they consider humans to be a small and petty spiecies incapable of great accomplishments.

Grand_Lunar
2007-Oct-06, 01:48 PM
As they consider humans to be a small and petty species incapable of great accomplishments.

I wonder if they describe themselves. :D

But I kid, of course!

They just aren't asking the right questions, nor taking in the right answers.

KaiYeves
2007-Oct-06, 04:56 PM
They just aren't asking the right questions, nor taking in the right answers.
"Ask the right questions or you will get the wrong answers." -No Such Thing as Magic?