Why do most photos of galaxies/stars say it took X amount of hours to capture? Can a single photo not be taken?
In: Physics
It is a single picture, but the camera was held open for a long time collecting photons.
Any photograph takes time to capture enough photons to make an image, but it’s usually measured in fractions of a second and not hours/days.
The reason astronomical objects like galaxies take so long to photograph is because they are so far away that there aren’t many photons from them that happen to hit the lense of the camera – they have had millions of years to spread out. So you need a longer time to collect enough photons to see an image.
Fun fact, there are actually a lot of nebulae and even galaxies that take up as much space in the sky as the full moon (the Andromeda Galaxy actually appears in the sky about five times the size of the moon – not making this up). The problem is they are much much farther away, so if you look up with your eyes, you might get a photon here and a photon there, but never enough to actually see the objects.
Cameras can collect information for a much longer period of time than our eyes before making an image, and they have larger areas from which they collect light. Think telescope lense compared to the side of a human pupil.
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