how do they calculate star distance?

[goku]

how do they calculate star distance?

[Jay-qu]

One such technique I know of is using parallax - Fairly detailed explanation ->

http://en.wikipedia.org/wiki/Parallax

[goku]

okay, but how do they know the measurment of the small top angle?

[Buffy]

They don't. Parallax is only useful out to a few thousand light years away, making use of the full width of the earth's orbit (e.g. measure one angle in January and another angle in July and triangulate).

For distances beyond that its possible within our own galaxy to use brightness/spectrum comparisons to do approximations. When you jump out to other galaxies, the primary method is to use the fact that there's a specific type of star known as a Cepheid, that is a variable star whose frequency is exactly in ratio to its apparent brightness, thus you can measure its frequency and its brightness and compute how far away it is. Every galaxy has a bunch of them, so its actually quite easy to map fairly accurate distances of all the galaxies we can see. Amazing visual maps of the universe have been generated by this method to show objects such as the "Great Wall", etc.

Check out the VRML link on this page: http://www.pbs.org/wgbh/nova/universe/tour_ggs.html

Cheers,
Buffy

[goku]

Originally Posted by Buffy

http://www.pbs.org/wgbh/nova/universe/tour_ggs.html

pretty pictures
a car is in the distance with it's radio and headlights on.
the brihgtness of the headlights is 10 candle power,
the decible level of the radio is 4.
how far away is the car?

[Qfwfq]

Clarification:

Originally Posted by Buffy

that is a variable star whose frequency is exactly in ratio to its apparent brightness

I'm sure Buffy meant absolute brightness, which can then be compared with the apparent brightness so as to compute how far away it is by the inverse square of distance rule.

The sequence of methods used for calculating larger distances, each based on information gleaned from measurements of less far distances, is called the cosmic ladder. It starts with parallax between simultaneous observations from different places on Earth. Once Earth's orbit was determined, the next steps were those Buffy mentions. Knowing the distances of many galaxies, Hubble noticed the proportionality of it to spectral redshift.

[goku]

how many of you actually think any of the methods work?
or do you just believe anything that a SCIENTIST says.

my point is, if the stars were that far away we would not be able to see them.
the farther away something gets the smaller it gets.

[Erasmus00]

Originally Posted by goku

my point is, if the stars were that far away we would not be able to see them.
the farther away something gets the smaller it gets.

It is true,the farther away something gets, the smaller it gets. However, how far must something be before you can no longer see it at all? On Earth, things tend to fade away in the distance because of atmospheric effects (the light gets scattered before it gets to you). Consider that you can see planets fairly well with a decent telescope still under the atmosphere. Now, stars are much larger then planets, and look to be just pin points in the night sky.

how many of you actually think any of the methods work?
or do you just believe anything that a SCIENTIST says

I find it far easier to believe that these methods work then that there is a global conspiracy of scientists out to distort things just for the hell of it.
-Will

[Turtle]

Originally Posted by goku

my point is, if the stars were that far away we would not be able to see them.
the farther away something gets the smaller it gets.

___Not true; the smaller it appears is the case. Your engagement of science appears to me to have no interest in adding to knowledge, either your own or others. I take the view that science is always ammendable & you make it clear that your view never is. Why do you bother? If you have in mind you will save me (us) in the name of some untestable belief, I offer you this: The last chosen is the first to go. I'll get in line when & if I choose.

[Tormod]

Originally Posted by goku

the farther away something gets the smaller it gets.

This is an interesting point of view.

Do a scientific experiment.

Bring a friend and stand back to back. Then leave your friend where he is and walk, say, 100 yards.

Has your friend shrunk? Have you? From your point of view, it is (or should be) obvious that YOU have not shrunk. Now, the question is: How do you know that your friend has not shrunk?