Why is it, when you see the earth from space, there are no stars in the background? What causes this, and why?

1 Answer
Mar 29, 2016

Answer:

In order to capture a clear image of the earth, which is quite bright when lit by the sun, the camera must be set to a fast shutter speed and low aperture. Under these conditions, the exposure is not sufficient to capture starlight.

Explanation:

In order for a camera to capture starlight, which is quite faint (yes, even from space!), it needs to be open lone enough to let in enough light to register on the sensor chip (or film). Cameras are not able to capture both bright and faint objects at the same time. You may have seen this in a photo where either part of the photograph is way overexposed, or else part is in virtual darkness.

You can simulate this yourself by going outside on a nice dark night with a sky full of stars, and take a photo of a friend using the camera flash. Your friend will be well lit, but the stars in the background will be invisible.

Conversely, if we are looking at a photo of the night side of Earth, the sun or moon may be in the background, also limiting the exposure. But some images of the night side of Earth from space, like the one below, DO show stars.

http://www.nasa.gov/content/iberian-peninsula-at-night