How big are the stars?

I'd like to get a basic grasp of why or how we know, or estimate the distance of the far away stars. One way for me to get a quick start is for someone to explain the following. If the earth, and solar system were the center of the universe, and the stars were, for some reason (this isn't a theory, just a base from which to understand) patterned in such a way as to get smaller the farther away they were - then how would we tell? In other words, as we looked in our telescope, and they appeared a certain size, what is it that we really can use to properly deduce the size (therefore distance?). That's already a lot for a thread, but, here's another. With the distant space probes, I believe even on opposite sides of the solar system, reaching the edge, apparenty having unexplainable 'slow down' effects, some have said it could mean a rethink on perhaps even the speed of light, or such basics. Others felt it was, although all attempts failed to explain it, probably something trivial. Could it be related to the speed of light?

I'm not an astrophyscist but I think I can give a roughly correct answer to you.If a star is larger or smaller it also varies in it's behaviour. A big start "burns" hotter and faster at the core. It produces more overall enegry and is brighter.Different stars also are different colors and this depends on the reactions going on in them, their size and other stuff I don't know about.You can't, I don't think, construct a pattern of stars that would work to produce the result you want.In addtion, a few stars are close enough to show a 'proper motion' and to have their distance measured directly by their parallex (they move against the background if you look from different positions).The physics of stars is reasonably well understood so you're scenario is a complete non-starter for several reasons.As for the slowing down of the voyagers, I don't think it is understood as yet. However, no one, that I am aware of, is throwing in a light speed change for that. You need to understand that 'c' the speed of light in a vacuum is a part of physics in other places. You can't change it without changing other things and those other things have been measured over a lot of time so there isn't any available evidence pointing to a change in c that I know of.

Arkathon - to put some flesh on the term parallax:
Go outside and look at something moderately distant - a tree, perhaps. Hold up your thumb, and look with your right eye at the thumb superimposed on the tree trunk. Then close the right eye and open the left. Your thumb "moves," right?This same thing happens when you look at "nearby" stars in january and again in July. The earth is 186,000,000 miles "left" of where it was before - clear across its orbit, and a star that's nearer - like your thumb - will shift against the background, distant stars. This effect was first measured in the 1830's, and was measured very accurately for a bunch of stars by the Hipparcos sattelite in the 1990's.As to the actual size of stars - they vary a great deal. In a scale model that I use for schoolkids, I make our Sun a beachball, 14 inches or 35 cm in diameter. The Earth is then a bb, 0.12 inch or 3 mm in diameter, 125 feet or 40 meters away. A white dwarf star is about the size of the Earth; a red supergiant is more like 500 feet in diameter.
And as for distances to other stars, the closest star in my model is another beachball 6000 miles from our beachball.Edit to answer one of your main questions: even the closest stars appear too small to "take a picture" of their size - sizes have to be measured or calculated by less direct methods like interferometry, or finding ones that get eclipsed by companion stars.[This message has been edited by Coragyps, 02-23-2004]

And to spell it correctly too!

So there would be no other known possibility that would make a star brighter? And is a brighter star then supposed to be bigger? Yes I would be quite surprised if I were to construct a pattern on this forum that was not thought of before. But already the answers seem to be good, and to the point, as far as man's knowledge goes. I guess you realized I was coming at it from a YEC perspective (This means young earth creation, no?) So then by glancing at the next post I see that the parralax is something like a difference of say, 186,000,000 miles in veiwpoints. How does this relate to how far away it is? In other words, whether we see it with the right, or left eye, how does it make it clearer as to distance in space. here's a couple links
BBC NEWS | Science/Nature | Mystery force tugs distant probes
Page not found – The Mars Mission – The Enterprise Mission
It seems the second link is an art bell type link, but seems interesting.

I'm trying to imagine how I can judge the distance of the tree, even though my thumb seems to have moved. I can see my thumb has moved, but how do I relate it to the tree? This seems like great distances, and a good way for children to understand them. What I'm trying to get, is, why is the basketball 6000 miles away, and not, for example 7000, or 500 miles? So we could tell one is farther away, cause it gets eclipsed, this is good. Now, what makes it any distance other than 'farther away'-wouldn't it still boil down to knowing how far one of the stars were at least?

It's not the tree in the analogy you are measuring the distance of - it is your thumb distance that would be measured based upon the angular change and some simple trigonometry.This has been done for thousands of stars with reasonable accuracy out to about 500 parsecs (approx. 1600 light years.) One light year is about 6 trillion miles.From the distance and the known luminosity of the star you can then calculate the diameter.The diameter can also be measured directly for a lot of stars now by interferometric techniques. In fact the difference in the polar and equatorial diameter of some fast rotating stars has been measured this way.

I've read the first one before and would note that "fanciful" is applied to some suggestions.The other one I can't comment on. I don't know how sensible it is.You seem to be doing something I have seen from YEC'ers before. Grasping desparately at straws trying to figure out someway the age measurements could be wrong.Whatever is learned here I think you will be disappointed in your hopes. There are a great number of things which make a 6,000 year old earth not a viable option. To think that this one anomoly is going to help sweep all the other things away is fanciful indeed.Why don't we all wait to see what is learned here. Meanwhile if you are so sure of your 6,000 year old figure you can go to dates and dating and start or find a thread there to show what is wrong with the dating methods.Even if c is actually changing it doesn't get you out of the hole all that easily.

Ok so we're getting there, about 1600 light years. Now how does one jump to millions of light years from this point of 'reasonable accuracy'? So far we seem within reason.

I see where this is going.Try doing a Google search on "cosmic distance ladder" and read some stuff. Any questions come on back.There are several ways of getting out to greater distances - some dependent on each other - some independent.Off the top of my head i can think of about 12 different methods.

I see you are not an optimist. I don't see any big disappointment so far. So now you think I'm in a hole? With the things you seem to read into some basic questions, I can see how you might be worried someone might think you read too much into your concepts of space and time. maybe someone will dig you out here and explain it.

Google search the following topics:parallax
secular parallax
dynamical parallax
spectroscopic parallax
spectroscopic binaries & distance determination
cepheid variables
RR Lyrae variables
planetary nebulae & distance measurement
Baade-Wesselink method
main sequence fitting
galactic maser & distance determination
proper motion & superluminal jets & distance determination
redshift distance determination
Sunyaev-Zeldovich effect
Type Ia supernovae & distance determinationThere are some others but thats a good starting list.

Those links are not really relevant to the discussion. The first is an old story about the anomalous acceleration problem (still unresolved) of some deep space probes.For a file which is directly relevant to the subjects being considered here, see Determining Distances to Astronomical Objects at talkorigins. This is quite a new FAQ. It does not address the size of stars, but it does address their distance, which seems to be under discussion here as well. What is nice about this FAQ is that it goes through a kind of ladder of distance measuring techniques, each one reaching further than the previous. The methods check on each other within the region of overlap. There is a section on parallax, wich a fairly straightforward description for beginners.Cheers -- Sylas

'links not relevant'---"Astonishingly, this new NASA evidence for a variable "speed of
light" (once properly interpreted!) is not unique.A compliation of recent scientific literature on the subject by
Lambert Dolphin (right), former physicist at the Stanford Research
Institute, reveals an historical body of published and unpublished
laboratory and astronomical evidence strongly supporting such a
radical interpretation -- directly contradicting what is taught
regarding the "inviolability of C" in current textbooks."
If there was any truth in this it would be relevant, no?
Thanks for your link. Theres a lot there. It seems there are some leaps of faith one must take to get much farther than the 1600 or so lightyears though.(I figure if the world were 6200 yrs old, looking at stars from either side of the world, travelling away from each other, we'd maybe have about 12,400 light years to play with) By the way, was there a reason that if stars were fantastically smaller way out there we would know it?

Not leaps of faith - inferences from observation. Well, I imagine that we know roughly how massive the stars are, by observing their gravitational effects, and from that and their luminance we can estimate what kind of nuclear processes are occuring, and from that, we can figure out what size they would have to be. Of course that relies on the laws of physics being the same in all parts of the universe, but that seems to be the case, as far as we can observe.