How does having long exposure help with distance in photos?

[Phys12]

The Hubble Space Telescope was able to take the Hubble Ultra-Deep Field Image thanks to the telescope being exposed to a single section of the sky for well over two months. But what I don't get is: how does keeping the telescope open for a long time help with catching distant objects? It can't be the case that it allows the light from that far away to reach us during that time, for it will have to be a big coincidence that we pointed only when it was first reaching us.

I tried to search for long exposure photography, but it mostly revealed how using that we can take pictures of moving objects differently by altering the exposure time. I couldn't find much on how it helps with seeing distant objects. How does it really work?

Correction: there were two sessions of observation-- one for over two months and the other for a little over a month.

 

[davenn]

Correction: there were two sessions of observation-- one for over two months and the other for a little over a month.

and you will find even those periods were not continuous as others would have booked time on the scope during those months for doing other research
there may have been an hour here and an hour there etc etc over a period of several months to get a final exposure time for a number of hoursDave

 

[Phys12]

and you will find even those periods were not continuous as others would have booked time on the scope during those months for doing other research
there may have been an hour here and an hour there etc etc over a period of several months to get a final exposure time for a number of hoursDave

And how exactly did all of this really help in imaging extremely distant galaxies?

 

[davenn]

And how exactly did all of this really help in imaging extremely distant galaxies?

because as you build up exposure time, you improve the signal to noise level and are able to image fainter objects or capture finer detailI will be doing the same thing tonite when I go out to image a comet and some other deep space objects
I will take a whole bunch of images and then stack them to produce a much better outcome than just a single exposureDave

 

[Phys12]

because as you build up exposure time, you improve the signal to noise level and are able to image fainter objects or capture finer detail

Dave

And all of this happens by keeping the shutter open for a longer time and stacking different images together? If we did not have an atmosphere, say, then could I make my own Ultra-Deep Field Image by using a typical observatory with, say, 10 m. diameter telescope (by of course, increasing the exposure time/stacking all the images)? Why/Why not?

 

[davenn]

on the system I am currently using, I can do a maximum of one minute exposures before tracking issues become a problem

so I could do a bunch of 1 min exposures tonite, some more in a few days time and may some more in a few week's time when the next clear sky happens

doing so I could accumulate an hour or so of data
some of my fellow astro guys have no problems doing 10 min exposures and then stacking dozens of them to make the equiv of several hours of exposure time

no atmosphere just gets rid of all the distortions caused by air movement, light pollution etcDave

 

[Phys12]

on the system I am currently using, I can do a maximum of one minute exposures before tracking issues become a problem

so I could do a bunch of 1 min exposures tonite, some more in a few days time and may some more in a few week's time when the next clear sky happens

doing so I could accumulate an hour or so of data
some of my fellow astro guys have no problems doing 10 min exposures and then stacking dozens of them to make the equiv of several hours of exposure time

no atmosphere just gets rid of all the distortions caused by air movement, light pollution etcDave

All right, thank you! :)