when your looking through a telescope or anything at all really to see farther into space are you accually seeing farther into space or are you mangnifing an image. Take a star for example that just burnt out. Do you see a burnt out star when you look through your telescope or does it still look like its there shining.
Since light travels at a fixed…and known speed, you are looking at events that occurred in the past. The term ‘real-time’ is a misnomer for observational purposes. For instance, a sufficiently powerful telescope could peer far enough into the past to see the last time my wife actually wanted to have sex.
IANAn Astronomer but a telescope only magnifies the image. The light that hits the surface of the objective lens of your telescope is exactly the same age as if it were to hit your unaided eye. What the telescope is then doing is spreading the field of view over a larger surface of your retina, thereby increasing its apparent size (which, in turn, dims the image’s brightness).
There is no way to see the object that you would like to observe as it would appear right then (not to mention the Relative can-o-worms that would open), unless you were actually within its vicinity in space.
kevsnyde: Not quite.
What the telescope actually does is collect more light than your eye can. Look at the difference in diameter between a telescope and your eye.
Think of it like a funnel in rain. The smaller funnel will not gather up as much water as the larger funnel.
As Ell said. In case of planets, the telescope does make them look bigger, but the increased light gathering of the telescope compensates. Plus, in the case of stars, they are always points sources no matter how much magnification you got in your backyard–so the main effect of the telescope is to gather more light.
Heh, I knew someone would nail me on this. Of course I didn’t mention that the bigger the lens the more it will compensate for the loss of brightness as you go up in magnification.
But was I wrong to state that the image is also being magnified as well? It makes the planet LOOK bigger because the light IS being spread out more (which would dim the image) over the surface of your retina, no? That is where, as I understood, the bigger the objective lens, the more you would compensate for this loss. I understand that under typical power we will still not resolve the discs of the distant stars, but that does not mean the light is not being magnified in size (or thereby, “spread out”).
Of course telescopes magnify, they have to. The large aperture compensates for the increased magnification, so the surface brightness doesn’t drop. But a telescope can’t increase the surface brightness of something. If you try to build a 100-mm aperture telescope with no magnification, the output beam ends up being 100mm wide which wouldn’t fit into your pupil. The only way to get around this is to use electronics, i.e. night vision systems. This doesn’t apply to point sources like stars, just extended objects.
Getting back to the OP, a burnt out star is a burnt out star no matter what instrument you use to observe it (besides a time machine, that is). A telescope does allow you to look farther out because things that are far away usually appear faint, and a telescope allows you to see fainter objects.
Several things going on here:
1.) A telescope does magnify the image you see. That is, when you look through a 7X telescope, the image of Mars, for instance, extends over 7 times the angular range it does when you look at it with your unaided eye.
2.) The large objective lens does indeed gather more light than your eye does, which makes that magnified image look brighter. But there’s another important reason for having a large objective lens:
3.) The larger the objective lens is, the smaller the distant objects you can resolve. The wave nature of light places a limit on the smallest object you can resolve. Thomas Young realized this around 1800, but the definitive work on resolution was done by George Biddell Airy, Astronomer Royal and director of Greenwich Observatory, circa 1835. He derived a lot of results in diffractive optics, but is probably most famous for the Airy Function and the Airy Disc – statements about how small the spot of light that forms the image of a distant object will be. The image has a dark right at 1.22 times the wavelength times the f/# of the telescope (f/# = focal length/diameter). If you cruch the numkbers through, you find that, even for the largest telescopes, the size of this Airy ddisc is larger than the magnified image of a distant star. Those spots of light you see in pictures of stars aren’t stellar diameters – they’re the limiting spots sizes defined by the telescope. (Using some exotic techniques, it has been possible to obtain the images of a couple of stars. AFAIK, the only stars besides our own sun that we have gotten real images of are Betelgeuse and Mira – pretty big stars and relatively close by). You can see why a big diameter is important – the bigger the diameter, the smaller the image, so the less “blurry” the image you see through the telescope is.
But tcburnett is also right. because light takes so long to travel to earth you can actually look at things that no longer exist. my physics teacher at school once said that, on average, when you look at a star you are looking back 7 years… that’s pretty cool i think.