Why can't we see stars in the sky when earth is filmed from space?

Question

Recently saw the 'Blue Planet' IMAX film which filmed the earth from a spacecraft. No stars were to be seen. Why is that?

I could find replies to dozens of these answers, positive and negative, but I just know there will still be contradictions! My choice of words could have been better ie. shuttle instead of space craft / space instead of sky..........

If filming from space, it wouldn't be considered the sky. I'm sure you just meant space ;) It seems everbody that explained light aperature and filmed solved your question. I just wanted to check in on it and star your question, an educated question at that :)

Just this one then. Yes, I did mean space not sky. And yes, to all contributors who explained about light aperature, I fully understand the explanations given and concur thank you.

Answer 1

The IMAX film was made on the space shuttle while it was in orbit. The Earth is bright, because it is lit by the sun. The stars are bright suns, but far away, and become faint points compared to the Earth. So, the stars don't show up on the film.
http://www.imax.com/ImaxWeb/filmDetail.do?type=nowPlaying&movieID=code__.__6768

This is the same as taking a picture of the moon with your camera. The camera won't see the stars, because they are relatively faint. However, if you take a ten second exposure, the stars will be seen in the picture. And the moon will be over exposed.

The camera would be set for infinity focus for the moon and the stars. And the camera must be held very still so the stars aren't blurred out. The atmosphere also blurs the stars a little. If the picture is longer than ten seconds, the stars will form little trails because the Earth is rotating as you take the picture.

Answer 2

Many of the answers already given are technically correct. Photographic film, and any digital picture chip as well, does not have the wide contrast range or large contrast ratio that the combination of human eye and processing power of the brain can achieve. The human visual system (eye and visual cortex in the brain combined) can give us a picture with a contrast ratio of 1million : 1, meaning we can perfectly well see together in the same view two different objects, one of which may be 1million times brighter or fainter than the other. Not so, in fact not nearly so, any photographic film or picture chip. Their exact contrast ratios vary by design, ranging anywhere from 200:1 at the low end to 10,000:1 at the high end. It would require heavy, time consuming picture editing from a combination of differently exposed pictures to pick out the good "raisins" of each exposure and combine them into the one "perfect picture" that would resemble what a human can see, or even more than that. Sometimes this is actually done (using Adobe Photoshop, for example). Check out some of the solar eclipse composite pictures of Fred Espenak on his web site www.mreclipse.com (seems temporarily down, hope it will be up again soon), also try http://sunearth.gsfc.nasa.gov/eclipse/solar.html

That is why the comparatively faint stars don't show up in an ordinary picture of planet earth from space. Neither do they show up in an ordinary picture of the moon if the exposure setting is optimized for detail rendition of the bright lunar surface, thus 'cutting out' surrounding faint stars.

Answer 3

You can't see the stars from a spacecraft taking photos of the earth because the stars are much farther from the earth than the spacecraft is, i.e., the starts are behind you.

If you turn the camera around to the opposite side of the space craft you will see plenty of stars. Heck, if you're lucky you may even see some Martians!

Answer 4

Darling, it's an IMAX!! All the Answers above want to be techy about aperture, shutter speed etc but why can't we see an IMAX film assembled from many sources which simulates what the "sky" WOULD look like IF IF we could film the Earth and the stars at the same time. They've had 30 years: surely a pastiche could be slapped together.

Answer 5

B`cos you are hanging in between the stars and the Earth. If you realy want to see the stars then either you turn back or go little more away from the Earth but you have to cover the distance of the space i.e just above the stars . under the film namely " Blue Planet " IMAX -wanted to show us the Earth thats by they filmed the earth from the spacecraft otherwise tthey could film from the earth just to cover the earth as well cover the stars in a sinngle shoot.
Is it not technical to understand it . And you must get reply to your question very well.

cheers
Rajan Sharma

Answer 6

You saw no stars because the film was exposed to bright sunlit scenes. When an object is bright, the film needs to be exposed for only a short time to form an image. Stars are faint objects. So when the exposure time is right for a spacesuit or the Earth lit by the sun, the stars simply do not have time to register on the film. if you went to the darkest site you could find here on Earth and took pictures at night using the same camera settings the astronauts used, you'd find no stars in your images either!

I hope this answer has helped you.

Answer 7

If you were in space yourself, you could see the stars--the human eye is far more ssensitive than most cameras. A long exposure shot will show them, though.

The reason is that light from the sun and the Earth (if you're in orbit) drowns out the starlight. To understand how this works, try this thought experiment (or do it for real if you wish):

Imagine a lamp (lit) on a table in the daytime. If you stand some distance away--or outside the house, looking in the windo---you will have a hard time seeing the light from the candle (if you see it at all). But at night, even someone driving past your house need only glance at the windo to see there's a light on inside.

And that's what happens to the stars--they're drowned outby all the other light.

Answer 8

I disagree, that it has to do with the aperture. (aperture = how much light enters the lens)

the simplest answer I come up with:

Your eyes can see more contrast, that the best lenses and photo/video equipment can reproduce.

Photographers are very aware of this.
Maybe you heard the saying : dont take a picture against the sun.
A photo/video camera needs to be set to the correct exposure for a certain light condition.
It is impossible for a photo/video camera to record the dark shadows and the bright highlights at the same time.

In other words, the range form dark to light captured by a camera is less, then what you are able to see with your eyes.

So if a camera is set to exposure the earth correctly, you will not see the stars, because they are beyond the range of the camera.

Try this:
a) Look at night at the start, while in a city street with bright street lights. You can not or just barely see stars.
When you look at the stars when its pitch dark around you, you can see way more stars.

b) take the following picture with your photo camera:
stand inside of a room in your house at day. take a picture where you frame a window so it fills half the frame, and the other half frame is the inside walls of your room. Take the picture when its really bright light outside.

Then take a look on the picture. Your camera will probably set the exposure so you can see the inside of your room in detail, but the window will be just a white square.
But when you look with your eyes, you can see all the details outside. (trees, street, etc.) and inside.

When you set the camera to exposure correclty on the bright window, you will see in your picture all the details outside, but whats inside your room will be so black, that you cant see anything. (thats exactly what happens when shooting the earth frm space)

Thats the reduced contrast a camera can capture, which is inferior to your eyes.

hope that helps to understand.

Answer 9

This is a remarkable question because it indicates that you are observant and thinking about what you observe at the same time.

The easiest way to answer your question is to compare your eyes to the camera that takes the pictures of the earth. Have you ever been on stage? When you are on a stage and you have these bright lights on you it is impossible to see anything past the first two rows of people.

This is like the camera that needs to focus light on the film. Because the earth is so bright the stars behind it are invisible on the film. In order to see the stars around the earth you would need to use a film that allows dimmer light to be ‘visible’ to the film. If you had film that sensitive the earth would be sooooo bright that it would look like a bright white light bulb! But, you would see the stars!

Answer 10

It takes a whole day for the Earth to complete a rotation, is that fast?... it depends on what your comparing it to, and its not just the earth thats moving, the sky out there is full of air and clouds that move, and the very stars themselves, entire galaxies, but they're all moving at different speeds in different directions and different ways... Its not a question of doubt if the earth is spinning, its a question of where is the moon or stars in relation to the earth at the time... As to motion blur, do look at the moon, it takes quite a bit of time to move across the sky, so in relation to us, its not moving all that fast. the same as the sun itself, if the Earth was spinning so fast as to cause motion blur a day would be over within a small number of hours (like 5 or less).. Actually the more I think about the question and scenarios of the Earth spinning faster, the more spun out I get! ... hehe take care, I hope it helped

Answer 11

Hi,
Actually, your answer is in your question. It is not the 'stars' that is being focused upon (see other answers giving technical info on apertures, etc.).
Haven't seen the film but would be interested if the camera panned to the point that earth was out of the picture and did the stars then become visible? If so, then the focal point was changed to account for the new distance.
Super question and brings to mind other possible answers!