(presentation for Powell Observatory Open House, March 24, 2007)
Astromomy is that rather awkward field of study for which the scientist has no control. Really, it is kind of disturbing. For the most part, all the poor astronomer can do is to choose when to look, and how to look. Normally, an astronomer cannot choose where to look from. I mean, we are afterall pretty much stuck on a planet named Earth, orbiting a star named the Sun, and that is executing its own orbit around a galaxy called the Milky Way, which is falling somewhat toward a cluster known as the Virgo cluster of galaxies. But the Milky Way is very large, and even though the Sun is cranking through space at an astounding 250 km/s (or around 150 miles every second), we are getting no where fast. Except for the Earth circuiting the Sun once a year, the poor astronomer is in effect stuck with having to view the entirety of the universe from one fixed position. There is no getting a look from another angle (at least not within my career span!).
So the problem is something like this. You are given food, water, a tent, a telephoto camera, and writing materials. You are told to go live on Buffalo Mountain for a year, with no internet or books or such things. You are asked to prepare a report on the diversity of nations present on the Earth, an overiview of their histories, and expectations for their futures, but without actually being allowed to travel anywhere. Best of luck!
The goals of the astronomer are somewhat similar. Every galaxy is a nation, and the stars its citizens. We can see it all, but we can't travel through it. So the issue of "perspective" is really of great importance for the astronomer.
What we fundamentally see is light, or the shining of objects. Now it helps us a great deal that light travels at a finite speed. What this means is that in the sense we do get to see the universe from a different perspective of a kind. The finite speed of light means that it takes time for the glow from a star to travel through space to us. The light we see from a star today is now how the star is today, but tells us how the star was when the glow arriving at the Earth today first left the star many years ago.
If you take a snapshot of the universe today, what you get is a view of planets, stars, and galaxies. But the more distant the object, the older the light that you see. So for objects that are farther away, the light is telling about their nature and properties when the obsnapshot of the universe today, what you get is a view of planets, stars, and galaxies. But the more distant the object, the older the light that you see. So for objects that are farther away, the light is telling about their nature and properties when those objects were younger, not how those objects are at this moment.
So looking to great distances is like seeing the universe at younger and younger ages, which is not too different from seeing the universe from a variety of different places. Here is an example of how this might work. Suppose that everyone came into this room with the same age of a teenager, but everyone ages really fast. And suppose that light travels really slow, maybe taking decades in person age to cross the room. And further, I am standing at the front of the room, with my eyes closed. When I open my eyes, what do I see? The front row will be filled with older people. The next row will appear to have slightly younger people, but those in the back row may still appear as teenagers. In fact, everyone in the room will be of the same age, but that is not how I will perceive. (And each of you will perceive rather different things as well!)
Astronomers have to take this and work backwards. We say, I know the speed of light. I see all of your ages. If I knew your distances, I could figure out how old each of you were when arriving. Lo and behold, you were all the same age.
Astronomy can make head aches, because you do have to think in this funny sort of way - realizing that you are stuck viewing almost everything from a fixed place but knowing that you are looking back into the past. Keeping this straight is not too bad, once you realize what is going on, and from our view and the time travel trickery, astromomers try to piece together a bigger picture of what is going on.
So when you are viewing telescopes here, remember that what you are seeing is the same view that everyone else on planet Earth is getting. And except for Solar System objects, it is the only view we ever get.