Science question, not word-related. In another thread, Seanahan said, "Didn't Hubble discover red shift around WWI?" I'd thought the red shift was known earlier, but my checking left me a bit more confused.
I found that Vesto Melvin Slipher discovered that galaxies outside our own have red shifts (It may be that he discovered the shift itself, not just that it is displayed by galaxies.) That discovery paved the way for Hubble's 1929 demonstration that the amount of a galaxy's red shift is proportionate to its distance (the distance being measured by Cephid variables). In other words, the farther away a galaxy is, the faster it is receding from us; that is, the universe is expanding.
But I'd thought that red shift had earlier been observed in stars, not just in galaxies, and had been used to measure star distances. Specifically, I'd thought that:
parallax can be used to determine the distances of a nearby stars (it's too small to measure for more distant ones);
in each such case, the star's distance was found to be proportionate to its red shift;
the shift/distance relationship thus deduced was used to calculate the distance of more distant stars, from their observed red shift.
I see that I was mistaken in the above, but I'm not sure of the details. Was red shift observed in stars in our own galaxy?
quote: Can this blinking star tell us how fast the universe is expanding? Many astronomers also believe it may also tell us the age of the universe! The photographed "Cepheid variable" star in M100 brightens and dims over the course of days as its atmosphere expands and contracts. A longer blinking cycle means an intrinsically brighter star. Cepheids variable stars are therefore used as distance indicators. By noting exactly how long the blinking period is and exactly how bright the star appears to be, one can tell the distance to the star and hence the star's parent galaxy. This distance can then be used to match-up easily measured recessional velocity ("redshift") with distance. Once this "Hubble relation" is determined for M100, it should be the same for all galaxies - and hence tell us how fast the universe is expanding. The exact magnitude of this calibration is under dispute and so a real live debate involving the value of Hubble's constant titled "The Scale of the Universe" will occur in April 1996 in Washington, DC.
Stars don't move apart from each other at constant rates. The Hubble proportion only works for galaxies outside the local cluster, where they're all moving apart as part of the cosmological expansion.
Stars in our own galaxy are moving in random directions, taking into account the gravitational attraction of the centre. So while you can see redshift in a star, and periodic variations in it can be used to detect binaries and planets, it's different for each star.
Before Hubble, nebulae were known: large fuzzy clusters outside the main body of the Galaxy, such as the Magellanic Clouds. One side of the Great Debate of the 1920s said they were just satellite clouds, the other side said they were other 'galaxies' in their own right, comparable in size to our own. Distances to some of the nearest ones could be estimated, and Vesto Slipher was first to see a relation with redshift. Hubble proposed the redshift effect applied to all of them, and that therefore nebulae were a vast sea of galaxies.
Obligatory linguistic nugget: for some reason astronomers generally write it redshift, not red shift.
As most of you should know, the universe is expanding. The expansion is not constant, but accelerating. The farther(uh oh, farther/further problems perhaps) away an object, the faster it is moving away from us. Thus is it difficult to detect redshift in objects in our own galaxy, because they aren't moving away from us very quickly. However, objects that are very far away have a noticeable redshift.
quote:If the universe contaiins everything, and the universe is expanding, what is it expanding into?
This question may be a little too big to address here. Here is a possible place to start reading:
quote: From http://www.weburbia.demon.co.uk/physics/centre.html The Big Bang as far as we understand it was not an explosion like that at all. It was an explosion of space, not an explosion in space. According to the standard models there was no space and time before the big bang. There was not even a "before" to speak of. So, the Big Bang was very different from any explosion we are accustomed to and it does not need to have a central point.
Bill Bryson's A Short History of Nearly Everthing makes a valiant attempt at explaining the Big Bang (and many other science questions). It's fun to read, as well!
Build a man a fire and he's warm for a day. Set a man on fire and he's warm for the rest of his life.
quote: If the universe contaiins everything, and the universe is expanding, what is it expanding into?
I remember asking one of my junior high science teachers this very question, and wondering why he was the teacher, since he didn't know the answer. Now I realize this one of those questions like "Does God exist?". Science knows no good answer. It helps to think of the universe as a balloon, with more and more air being blown in. The outside of the balloon is still the boundary of the universe, and contains everything, but it contains more and more air as time goes by. Luckily, there is no analogy for the popping of the balloon.
Of course, the universe is defined as "everything", so there is no air to blow into the balloon that isn't already part of the universe. Another term is needed to describe this, but for lack of it, universe pulls double duty.
