MadSci Network: Astronomy
Query:

Re: why can i see the stars at night but pics of space look like a black void

Date: Thu Apr 6 21:52:38 2000
Posted By: Neil Sandham, Secondary School Teacher, Science Teacher and Career and Technology Studies Coordinator, Chestermere Middle School
Area of science: Astronomy
ID: 954816815.As
Message:

First off, most of the time that you see pictures from space, the camera is pointed towards the planet, not into outer space. Therefore, you don’t see many stars in the background, because the earth is in the background.

For those shots where the subject seems to be near the edges of the planet, you can’t usually see stars because

  1. The camera may be focused on the subject only, so it doesn’t pick up much in the background (not usually a problem with modern cameras anymore).

  2. The sunlight bouncing of the earth (or other object) is too bright for you to see the relatively dim stars in the background (in effect it overloads the film).

Another problem is due to the length of time the film is exposed. In order for the faint starlight to be picked up on film you need to keep the shutter open on your camera for several seconds, otherwise, all you get is a dark frame. Most of the pictures you see are from video images, which don’t use a wide enough aperture or exposure setting (lens opening) to take in the background starlight. On top of this, according to Kodak NASA tests all of the film they use to make sure it can withstand the intense radiation of outer space better than standard film, otherwise (as John Glenn found out) space-based photos can show up as overexposed, foggy pictures.

Finally, you can see stars in space-based photography. The Hubble Space Telescope uses digital cameras and magnifying mirrors to capture images of stars and other phenomena. What I think you are referring to (although I am guessing here) is that, pictures taken near the earth’s outer atmospheric layers may be subject to a similar distortion as we experience when viewing them from Earth. This is one of the main reasons why the Hubble Space Telescope was launched: so we can observe stars and space phenomena without the distortion caused by the light passing through the many layers of our atmosphere.

You might also be interested in an amateur’s advice on taking star pictures from Earth.


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