Expert: Paul Wagner - 2/20/2005

Question
I guess my main question would be if a telescope has been aimed in one direction for more than just a few hours... like more then one year.  As you stated below it might only be a slight change after being aimed in one spot and coming back to it.  

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Followup To
Question -
Paul,

I hope you are able to understand my question.  As I learned in astronomy you sometimes see things in the past instead of the present. (such as looking at the sun, you look at it ___ secs ago instead of present since it takes light time to travel to the human eye)  I was wondering what was the longest time a telescope has been placed to look in ONE AREA of space and have information fed to it. (for example: seeing galaxies many years ago, and watching them change over present time (but at the same time it is really past time).  Thank you.

Mike
Answer -
Dear Mike:

Telescopes have been aimed at one section of the sky for a few hours, to capture all the light from that area.  This is how astronomers let the light hit film to take photographs of very dim objects.  But remember that while the telescope may be aimed at a part of the sky for a few hours...galaxies usually don't change that fast, so you don't usually see any changes.

Imagine if you were looking at the moon--even if you looked at it for several hours, it wouldn't change much.  Because the distances and the size of the objects we study in astronomy are so huge, we usually can only get a snapshot of what they look like. To understand how things change, we usually have to come back years later and compare the images.  Even then, the changes are usually very slight.

Paul Wagner  

Answer
Dear Mike:

The real issue here is how quickly things change. Except for a few very rare situations, the stars arounds us haven't changed noticeably in 2000 years. So even if the scope had been pointed in that direction for 2000 years, we wouldn't have much to talk about.  

There are some stars that do change, called variable stars, and they have been recorded exactly as you suggest--by watching them for long periods of time, a measuring how they change.  Some change over a period of years, others over periods of weeks, days, or even seconds.

And don't forget that telecopes are not TV cameras.  They accumulate light, so that the image is a summary of all that time onto one image, one photograph.  To detect variable stars, astronomers had to compare one photograph with the next, to see how one of the stars was different.

Paul Wagner