APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

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APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by APOD Robot » Sun Aug 02, 2015 4:07 am

Image Apollo 17 at Shorty Crater

Explanation: On the Moon, it is easy to remember where you parked. In December of 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt spent about 75 hours on the Moon in the Taurus-Littrow valley, while colleague Ronald Evans orbited overhead. This sharp image was taken by Cernan as he and Schmitt roamed the valley floor. The image shows Schmitt on the left with the lunar rover at the edge of Shorty Crater, near the spot where geologist Schmitt discovered orange lunar soil. The Apollo 17 crew returned with 110 kilograms of rock and soil samples, more than was returned from any of the other lunar landing sites. Now forty three years later, Cernan and Schmitt are still the last to walk on the Moon.

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kwistutwel

Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by kwistutwel » Sun Aug 02, 2015 7:16 am

Title should have been: Now where did i leave my car?
or: Dude, where's my car?
:mrgreen:

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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by madtom1999 » Sun Aug 02, 2015 7:45 am

CGI was so much better in those days.

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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by PeteBataleck » Sun Aug 02, 2015 8:41 am

Why are there no stars visible ?

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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by Ann » Sun Aug 02, 2015 9:45 am

PeteBataleck wrote:Why are there no stars visible ?
It's daytime. The sun is up. Note the sharp shadow below the lunar rover. The mountains in the distance are brightly lit up by the Sun.
Image
The picture on the left is a Hubble image of a giant planet orbiting the star Fomalhaut. In order to see the planet, astronomers had to blot out the overwhelming brilliance of the star by covering it with a mask. The mask is the round black shape near the middle of the picture. Note that brilliant bright rays of starlight still escape from the edges of the mask.
Lunar eclipse. Mt. Lemmon SkyCenter/University of Arizona
In order to see the stars from the Moon when the Sun is up you'd better wait for an eclipse, when the shadow of the Earth covers the Moon and makes the lunar landscape dark.

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hoohaw

Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by hoohaw » Sun Aug 02, 2015 10:45 am

Takes me right back! I was in Houston during the entire mission, in "Spectrometers," where we monitored our experiment which was on the orbiter, not the lander. As the orbiter returned to Earth, there were three sleep periods of eight hours, during which the capsule rotated to keep the temperature even. It was I who decided in what direction the rotation axis would point, during each of the three sleep periods, so our spectrometer would scan across interesting astronomical targets. And during the last of the three sleep periods, we and all the other science experiment types were invited into the famous control room for Chinese food! I was young then; I am old now. Those were the days, my friends, we thought they'd never end....

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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by Boomer12k » Sun Aug 02, 2015 12:16 pm

Send Rovers...they are cheaper, and do a pretty good job...

Always a nice picture.
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by henrystar » Sun Aug 02, 2015 12:43 pm

Boomer12k wrote:Send Rovers...they are cheaper, and do a pretty good job...
:---[===] *
That is how I feel about Mars, for sure! But gosh, Moon is SO close and is SO easy to get to - my inner Space Cadet wants people on the Moon!

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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by Ron-Astro Pharmacist » Sun Aug 02, 2015 2:59 pm

madtom1999 wrote:CGI was so much better in those days.
Apollo Moon Article (2).jpg
I have a possible theory about why the Apollo moon missions were thought to have been faked. Around the time newspaper journalists published articles like this Statesman’s Family Weekly from July 13, 1969. It states “Astronauts Edwin (Buzz) Aldrin (left) and Neil Armstrong go through a full-dress rehearsal of their lunar-surface activities. Aldrin uses tong and scoop to pick up moon rocks. Armstrong holds open plastic bag for samples and photographs the operation.”

Of course – if they “faked” it once on a practice set why wouldn’t they fake it for real? And these were featured in newspapers around the country. Sure not many really believed they faked it but some did - always suspecting a conspiracy after Kennedy’s assignation.

When I saw this in my Dad’s collection it’s been on my mind that covers like this added to the faking theories of the time.

Body of Article (most)
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by Coil_Smoke » Sun Aug 02, 2015 3:24 pm

Ann wrote:
PeteBataleck wrote:Why are there no stars visible ?
It's daytime. The sun is up. Note the sharp shadow below the lunar rover. The mountains in the distance are brightly lit up by the Sun.
Image
The picture on the left is a Hubble image of a giant planet orbiting the star Fomalhaut. In order to see the planet, astronomers had to blot out the overwhelming brilliance of the star by covering it with a mask. The mask is the round black shape near the middle of the picture. Note that brilliant bright rays of starlight still escape from the edges of the mask.
Lunar eclipse. Mt. Lemmon SkyCenter/University of Arizona
In order to see the stars from the Moon when the Sun is up you'd better wait for an eclipse, when the shadow of the Earth covers the Moon and makes the lunar landscape dark.

Ann
The Sun would probably set on Earth's moon while waiting for Earth to eclipse old Sol. Either way the stars would become far easier to see. You will have two earth weeks to admire that amazing, clear, sharp and vivid view of the heavens. Dress warm. I hear those long Lunar nights are a bit chilly.

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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by Joe Stieber » Sun Aug 02, 2015 4:56 pm

PeteBataleck wrote:Why are there no stars visible ?
Today's APOD is obviously well exposed for a sunlit scene. Here on earth, which is essentially the same distance from the light source (the sun), the old rule-of-thumb from back in the days of film was that a sunlit scene with distinct shadows would be properly exposed by using a shutter speed that was the inverse of ASA film speed (now ISO) at f/16. For example, if they were using ASA 64 film, it would have been exposed approximately 1/60 second at f/16 (or some combination that gives the same exposure value, like 1/250 at f/8).

If you were to use a modern digital camera on a clear dark night here on earth, and take a picture of the sky with that exposure set manually, you'd get nothing. For comparison, to get a nice snapshot of a well-populated star field from a dark site, I might use a typical exposure of 6 seconds at f/4, ISO 6400. That's a difference of more than 19 photo stops, or more than 500,000 times as much exposure as a standard daylight scene.

Quite simply, you can't capture dim stars with a brief exposure that works well for a bright daylight scene, whether you're on the earth or the moon, even if the moon doesn't have interference from a blue sky.

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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by BMAONE23 » Sun Aug 02, 2015 5:16 pm

PeteBataleck wrote:Why are there no stars visible ?
Seems like every time a picture of a Lunarscape is an APOD, this question arises. At first you would think this because it Is the Moon and the sky is black without atmosphere and so should be teeming with stars. Consider that the Moon also has a rather dark surface, about the color of asphalt paving. So a good experiment would be to go to your nearest store parking lot at night (reasonably well lit). Spread out something to lay on and lay down, Now look up at the sky under the relatively DIM light of 70 watt HP Sodium Vapor lamps and see how many stars you can see. Now imagine the Light Source being as bright as the Sun. Although consider that the Sun puts out about 130 Watts of light per square foot on earth and a Street light comes nowhere near that.

Now consider the Shutter Speed of the camera to allow for the highly illuminated scene without bleeding or overexposure.
The main reason why Stars cannot be seen in Lunar surface images is that the camera shutter isn't open long enough to allow for capturing their relative dimness in contrast to the Lunar Surface apparent brightness.

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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by alter-ego » Sun Aug 02, 2015 5:38 pm

BMAONE23 wrote:
PeteBataleck wrote:Why are there no stars visible ?
Seems like every time a picture of a Lunarscape is an APOD, this question arises. At first you would think this because it Is the Moon and the sky is black without atmosphere and so should be teeming with stars. Consider that the Moon also has a rather dark surface, about the color of asphalt paving. So a good experiment would be to go to your nearest store parking lot at night (reasonably well lit). Spread out something to lay on and lay down, Now look up at the sky under the relatively DIM light of 70 watt HP Sodium Vapor lamps and see how many stars you can see. Now imagine the Light Source being as bright as the Sun. Although consider that the Sun puts out about 130 Watts of light per square foot on earth and a Street light comes nowhere near that.

Now consider the Shutter Speed of the camera to allow for the highly illuminated scene without bleeding or overexposure.
The main reason why Stars cannot be seen in Lunar surface images is that the camera shutter isn't open long enough to allow for capturing their relative dimness in contrast to the Lunar Surface apparent brightness.
I can't speak to the correlation of the image test parameters to the actual lunar photo parameters, but the principles are effectively demonstrated here.
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by ta152h0 » Mon Aug 03, 2015 3:08 am

I think the people that repeat the " why are stars not visible ? are part of a UFO guys group that refuse to believe " we " have walked on the moon and this was staged in a Hollywood studio. An automatic ignore button is probably very usefull in this case. I have no idea how many times Mr Peterson has patiently discussed " saturation "
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by alter-ego » Mon Aug 03, 2015 3:57 am

ta152h0 wrote:I think the people that repeat the " why are stars not visible ? are part of a UFO guys group that refuse to believe " we " have walked on the moon and this was staged in a Hollywood studio. An automatic ignore button is probably very usefull in this case. I have no idea how many times Mr Peterson has patiently discussed " saturation "
I don't know how many "repeats" there are, but the fact is it's a valid question that's likely to be asked again. The newbies most likely aren't aware of all the previous discussions and for those a sincere reply is warranted. Of course there'll always be conspiracy theorists who normally make themselves known pretty quickly.
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by geckzilla » Mon Aug 03, 2015 4:33 am

It's also a valid question how often the question is valid... one must wonder how many people ask it out of genuine curiosity or temporary incredulity rather than as a rhetorical opening for a moon hoax exposé.
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by owlice » Mon Aug 03, 2015 1:45 pm

PeteBataleck wrote:Why are there no stars visible ?
How often do you see stars in a daytime sky?
Ron-Astro Pharmacist wrote:I have a possible theory about why the Apollo moon missions were thought to have been faked.
I do, too, but I'd have to moderate my own post if I were to post it! :mrgreen:
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by Chris Peterson » Mon Aug 03, 2015 3:13 pm

owlice wrote:
PeteBataleck wrote:Why are there no stars visible ?
How often do you see stars in a daytime sky?
But there is a difference. The stars are easily visible in the daytime lunar sky to an astronaut. And you could use a telescope during the lunar day to study faint nebulas just as well as you could at night. The main reason we don't see stars in the day on Earth isn't because of dark adaptation, but because light scattered by the atmosphere hides them. Obviously, that doesn't happen on the Moon.

The reason stars don't show up in so many planetary astronomical images is because the exposure is adjusted for the much brighter foreground objects. But that's primarily an instrumental limitation that impacts our vision much less.
Chris

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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by neufer » Mon Aug 03, 2015 4:25 pm

Chris Peterson wrote:
owlice wrote:
PeteBataleck wrote:
Why are there no stars visible ?
How often do you see stars in a daytime sky?
But there is a difference. The stars are easily visible in the daytime lunar sky to an astronaut.
And you could use a telescope during the lunar day to study faint nebulas just as well as you could at night.
  • Both the astronaut's helmet and/or telescope would have to very carefully avoid
    any stray light coming from either the Sun, Moon, Earth or LEM.

    Neil Armstrong's statements made when the command module had just first entered lunar shadow
    such that there was no stray light coming from either the Sun, Moon, Earth, or LEM.:
http://history.nasa.gov/ap11fj/11day4-loi1.htm wrote:
Apollo 11 : Day 4, part 1: Entering Lunar Orbit

071:59:20 Armstrong: Houston, it's been a real change for us. Now we're able to see stars again and recognize constellations for the first time on the trip. It's - the sky is full of stars. Just like the night side of Earth. But all the way here, we've only been able to see stars occasionally and perhaps through the monocular, but not recognize any star patterns.

[Corrected Transcript and Commentary Copyright © 2009 by W. David Woods, Kenneth D. MacTaggart and Frank O'Brien]
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by Chris Peterson » Mon Aug 03, 2015 5:03 pm

neufer wrote:Both the astronaut's helmet and/or telescope would have to very carefully avoid
any stray light coming from either the Sun, Moon, Earth or LEM.
Of course. But that's just a simple engineering issue, nothing to do with the actual visibility of stars on an airless, sunlit body as opposed to their visibility on a body with a significant atmosphere.
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by neufer » Mon Aug 03, 2015 6:07 pm

Chris Peterson wrote:
neufer wrote:
Both the astronaut's helmet and/or telescope would have to very carefully avoid any stray light coming from either the Sun, Moon, Earth or LEM.
Of course. But that's just a simple engineering issue, nothing to do with the actual visibility of stars on an airless,
sunlit body as opposed to their visibility on a body with a significant atmosphere.
It has a lot to do with whether 12 Apollo astronauts ever had the capability to observe stars from the surface of the moon.
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by Chris Peterson » Mon Aug 03, 2015 6:12 pm

neufer wrote:
Chris Peterson wrote:Of course. But that's just a simple engineering issue, nothing to do with the actual visibility of stars on an airless, sunlit body as opposed to their visibility on a body with a significant atmosphere.
It has a lot to do with whether 12 Apollo astronauts ever had the capability to observe stars from the surface of the moon.
Actually, the ability of the Apollo astronauts to observe stars is irrelevant to the issue under discussion, which is the distinction between seeing stars in photographs and the ability to see them visually on an airless body.
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by ta152h0 » Mon Aug 03, 2015 9:08 pm

Didn't Apollo 13 astronauts use stars to navigate and calculate burn times and when to " hit the button " ???
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Re: APOD: Apollo 17 at Shorty Crater (2015 Aug 02)

Post by alter-ego » Tue Aug 04, 2015 3:20 am

ta152h0 wrote:Didn't Apollo 13 astronauts use stars to navigate and calculate burn times and when to " hit the button " ???
Although it's possible to see stars from the ISS with the inside lights out (like trying to see stars out your living room window with the room lights on), the manually-initiated correction burn for the stricken Apollo 13 was done using the Sun as the alignment star:
https://www.nasa.gov/mission_pages/apollo/missions/apollo13.html#.VcApxHzJDRY wrote:...
The command module navigational platform alignment was transferred to the LM, but verifying alignment was difficult. Ordinarily the alignment procedure uses an onboard sextant device, called the Alignment Optical Telescope, or AOT, to find a suitable navigation star. Then with the help of an onboard computer, it verifies the guidance platform's alignment. However, due to the explosion, a swarm of debris from the ruptured service module made it impossible to sight real stars. An alternate procedure was developed to use the sun as an alignment star. Lovell rotated the spacecraft to the attitude Houston had requested and when he looked through the AOT, the sun was just where it was expected. The alignment with the sun proved to be less than 1/2 a degree off. The ground and crew then knew they could do the five-minute P.C. + 2 burn with assurance, cutting the total time of their voyage to about 142 hours. At 73 hours, 46 minutes into the mission, the air-to-ground transcript describes the event:

Lovell: OK. We got it. I think we got it. What diameter was it?
Haise: Yes. It's coming back in. Just a second.
Lovell: Yes, yaw's coming back in. Just about it.
Haise: Yaw is in....
Lovell: What have you got?
Haise: Upper-right corner of the sun....
Lovell: We've got it! If we raised our voices, I submit it was justified.
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