Earth at Twilight (APOD 27 Dec 2007)

orin stepanek · Post by **orin stepanek** » Thu Dec 27, 2007 1:34 pm

http://antwrp.gsfc.nasa.gov/apod/ap071227.html
A stunning view! You can see the thickness of the blue atmosphere at the top. I like the way it seems to narrow as it disappears into the dark side. With out the space program photos like this would not be possible. The Earth is the most beautiful planet I have seen so far. I don't know if we will ever see an exoplanet that may compare.

Orin

scopdrvr · Post by **scopdrvr** » Fri Dec 28, 2007 5:20 pm

On the right side of the photo the atmosphere is green in a distinct layer beneath the blue layer. I imagine the cause of this might be related to the "green flash", but does anyone have a more complete explanation?

elvis1 · Post by **elvis1** » Sat Dec 29, 2007 6:36 am

Can some one tell me why in all the pictures I see, like the one today of EARTH, and one in SEPT. of a space walk, the whole background is black but you can not see one STAR, if it is that dark (black) out there I would think that the stars should show in these pictures. thank you.

orin stepanek · Post by **orin stepanek** » Sat Dec 29, 2007 4:58 pm

elvis1 wrote:Can some one tell me why in all the pictures I see, like the one today of EARTH, and one in SEPT. of a space walk, the whole background is black but you can not see one STAR, if it is that dark (black) out there I would think that the stars should show in these pictures. thank you.

The Earth pretty much dominates the view here. I'm sure if you pointed the camera away from the Earth and toward the darkness of space you would see some stars. Longer exposures would probably bring out a few stars but then the picture of Earth would probably get washed out pretty bad.
Orin

BMAONE23 · Post by **BMAONE23** » Sat Dec 29, 2007 6:04 pm

Looking at the full size image, I see, near the upper left corner of the picture, what is either a couple of bad pixels or a white and blue star.
I needed to view the full size image as I moved the side bar to pick up the colored pixels

orin stepanek · Post by **orin stepanek** » Sat Dec 29, 2007 6:25 pm

BMAONE23 wrote:Looking at the full size image, I see, near the upper left corner of the picture, what is either a couple of bad pixels or a white and blue star.
I needed to view the full size image as I moved the side bar to pick up the colored pixels

I had to use the magnification on my computer to blow the picture up another 400% and I found two more dimmer pixels to the right and a little lower than the one you described so I'm thinking that they must indeed be stars. Nice find BMAONE23.

Orin

Case · Post by **Case** » Sat Dec 29, 2007 6:43 pm

BMAONE23 wrote:Looking at the full size image, I see, near the upper left corner of the picture, what is either a couple of bad pixels or a white and blue star. I needed to view the full size image as I moved the side bar to pick up the colored pixels

A photoshopped enhanced version of the image shows many small dots, with approximately the same distribution "above" the Earth as in the Earth's shadow. That suggests to me that they aren't stars.

What I can't figure out, though, is the nature of the shadow/dark spot in the lower right corner. The image is said to be taken 4 days before the June 21, 2001 eclipse; so that can't be it.

BMAONE23 · Post by **BMAONE23** » Sat Dec 29, 2007 8:18 pm

I was wondersing about that lower right corner "dark spot" myself.

Qev · Post by **Qev** » Sun Dec 30, 2007 2:33 am

Maybe it's the edge of the photographer's thumb?

I have no idea what that could be, otherwise. It's four days off and half the world away from the solar eclipse that occurred the month the photo was taken.

DavidLeodis · Post by **DavidLeodis** » Sun Dec 30, 2007 1:26 pm

I wonder if the 'dark spot' in the lower right could be a small part of an eye of an hurricane?

One thing that is confusing me (easily done I admit!) is that when the "this gorgeous view" is clicked on when online that brings up the image in the Gateway to Astronaut Photography of Earth website. In the image data (under Nadir) it indicates that the image was taken on 2001/06/17 at 21:51:05. However, in a labelled image in that webpage (and others that can be brought up from that webpage) it has the same date but gives a time of 22:33:05. That may be the time when the image was released, but, unless Nadir time is different from normal time, it is confusing.

NoelC · Post by **NoelC** » Sun Dec 30, 2007 8:41 pm

elvis1 wrote:Can some one tell me why in all the pictures I see, like the one today of EARTH, and one in SEPT. of a space walk, the whole background is black but you can not see one STAR, if it is that dark (black) out there I would think that the stars should show in these pictures. thank you.

Already answered above, but I'll elaborate a bit:

For objects in the sun (e.g., the Earth, or spacewalkers) a VERY short exposure time is required. It's just the same as if you're photographing someone outside on a sunny day - you'll have exposure times like 1/500th of a second. The stars are simply too dim to show in such exposures. By contrast, a night exposure that will show stars can actually be in multiple SECONDS, instead of a small fraction of a second.

The dynamic range of a camera just isn't wide enough to capture both the very dim stars and the sunlit subjects at the same time.

-Noel

Chris Peterson · Post by **Chris Peterson** » Sun Jan 06, 2008 1:12 am

NoelC wrote:The dynamic range of a camera just isn't wide enough to capture both the very dim stars and the sunlit subjects at the same time.

One additional comment: it is often believed that the stars appear exceptionally bright or numerous from space, but in fact, the attenuation of the atmosphere is slight- not more than a few tenths of a magnitude at the zenith. So a camera used in space will respond to stars the same as one used on Earth at night. And the sunlit Earth from space will look the same to the camera as the sunlit ground would from below.

This applies also to the APOD showing the Milky Way from an elevation of 5000 meters. Visually, this altitude makes almost no difference to the appearance of the sky. The limiting magnitude is about the same at any dark sky site in the world, regardless of elevation.

orin stepanek · Post by **orin stepanek** » Wed Jan 16, 2008 11:43 pm

Qev wrote:Maybe it's the edge of the photographer's thumb?

I have no idea what that could be, otherwise. It's four days off and half the world away from the solar eclipse that occurred the month the photo was taken.

It don't look like a huricane. It may be a thumb of finger, or maybe a shadow from the space station.
Orin

craterchains · Post by **craterchains** » Thu Jan 17, 2008 12:47 am

Possibly the edge of the window on the International Space Station.

iamlucky13 · Post by **iamlucky13** » Thu Jan 17, 2008 7:53 pm

craterchains wrote:Possibly the edge of the window on the International Space Station.

There's a couple of good guesses, but this is the one I'd most likely subscribe to. Unless the shadowy feature is something soft-edged in the atmosphere, it's quite out of focus, so it's close to the camera. Even if it were something only slightly further away, like the Quest airlock, it should be in better focus than we see.

My first thought had been vignetting from a lens with a small image circle, but the orientation is wrong.

The windows are pretty small on the ISS. The astronauts will be in for quite a treat next year when the cupola gets installed.

Chandler22 · Post by **Chandler22** » Mon Jan 21, 2008 7:31 pm

After looking at this picture i really like the close up picture of the earth from outer space. it shows how dark outer space is and how the blue the earth is with some red parts that stand out in the picture to.

Starship Asterisk*

Earth at Twilight (APOD 27 Dec 2007)

Earth at Twilight (APOD 27 Dec 2007)

Earth at Twilight (APOD December 27 2007)