Why does one need a long exposure time if one makes pictures of galaxies for example?

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Why does one need a long exposure time if one makes pictures of galaxies for example?


In: Technology

The light from galaxies, stars and other objects in the night sky is very weak, so the camera needs more time to ‘gather’ light to make the photo. Think of all of the light going into the camera being layered on top of each other, overlapping which makes each light source brighter. Other camera things come into play aswell such as the ISO and the Aperture of the camera. A higher ISO makes the sensor more sensitive to light, but the image will be more grainy. The Aperture is the size of the opening on the camera, pretty much the same as how your pupil changes size to adjust to low light areas, or very bright areas. Aperture allows more light to get into the sensor so, the camera can gather more light quicker. Aperture is measured in F stop numbers. The lower the F stop the wider the aperture = less light gathered, and a dimmer photo.

I probably missed some stuff but that’s the basic reason why.

The longer the exposure is open in a camera more light can be let in. With stars being so far away it requires a longer exposure time to collect the light given off to be visible.