In Astronomy it is common to see 30 minute exposures.....?

Question

It is common for people to use 30 minute exposures in Astronomy. Like this pic here.......

http://www.celestron.com/c2/image_view.php?FileID=124

Why did he use a 30 minute exposure, and how is that different from a regular snapshot?

Answer 1

It's not at all uncommon to use exposure times of an hour or more for very faint objects. If the radiance is low enough, it may take over an hour to collect enough photons to actually be seen on the film (or on the surface of a CCD detector).

HTH ☺

Doug

Answer 2

Yes, it is very common. The light coming from most deep sky objects is very faint. To the naked eye, even through an 8" telescope, the Ring Nebula is just a fuzzy batch of bluish light. You can't see any color. Long exposures bring out the color.

Of course, the larger the telescope you use the brighter an object will appear and exposure times would be shorter. However, nothing ever appears like it does in photographs because your eyes can't take long exposures.

Big research telescopes look at extremely faint objects so they still use very long exposures. The famous "Deep Field" photograph by the Hubble telescope was something like 100 hours of exposure time...in order to pick up the faintest objects in the universe.

Answer 3

A regular snapshot wont even get close to what you can see with your eye. The faint star you can see in the middle of the ring is just about on the limit of what you can see in an 8" 'scope, but it's still not bright in a 30 minute exposure.

Answer 4

A snapshot would show you about what your eye could see, or maybe less, depending on the sensitivity of the camera. By accumulating photons for longer periods of time, an astro camera can bring out details far fainter than what you could see with your eye at the eyepiece. Exposures can even be spread over several nights, and multiple images combined in the computer to reveal very faint details.

Answer 5

i take pictures like this with my digital camera. you need to have a camera that allows the shutter to stay open for extended periods of time so that the faint light can collect on the cameras sensor. you will also need a telescope that can track the object you are trying to photograph. if you want to try and take simple pictures of the constellations you dont need to leave the shutter open too long. maybe 20-30 seconds depending on the type of cmera...good luck!!!!

Answer 6

Basically I agree with thankyoumaskedman and Edwin. Manual mode, tripod, Bulb setting. There are remotes that will do the timing for you. Even more interesting is an intervalometer, which will open the shutter periodically. Handy for time lapse photography.