Noob Question - How do people measure dis?tance of stars and galaxies far away

[Sashatheman]

I read that people can measure stars using paralax , but only if the stars are within 400 light years away. But How do we measure stuff further away. Is there more then one method to measure far away objects?

 

Reason i am asking is that a guy i was talking to told me, that scientists can only measure stars accurately using the parallax method, and anything further then that are just "guesses". I knew he was wrong, but i didnt know how to reply to him. So yeh i would really like to know some info.

 

ps Does redshift have much to do with it?

[YT2095]

don`t quote me, but I think red shift gives an indication of speed it`s traveling when compared to the spectroscopy of known elements and their "Finger prints", rather than actual Distance.

[m4rc]

The parallax method is the method which depends on the least number of assumptions. The red shift method can be used but the only reason that we can assume that the distance is related to the red-shift is that it has been verified using other methods.

 

Another method is to measure the brightness of a star/galaxy and assume the amount of light emitted by that star/gallaxy (absolute brightness). The measured brightness of the star will decrease with distance ([math]1/r^2 [/math] law). In some cases the astronomers can make accurate assumptions of absolute brightness of a star.

Red giants, Cepheid variables, Type Ia Supernovae are 3 types of standard candles (see http://en.wikipedia.org/wiki/Standard_candle ). I believe that their distance of some of these were first measured using the parallax method. Using this data, it was noticed that their absolute brigtness was predictable so their brightness could be applied to measure the distances beyond what is possible with the parallax method.

[5614]

At large distances the parallax method becomes hard to accurately measure because the angles involved become very small. Your friend said scientists can only measure distances to stars, I'd say they can measure the distance to any object, but for an accurate measurement it cannot be too far away. The parallax method only works up to a few hundred light years away.

 

The parallax method was used to measure the distance to our nearest (after the sun) star and measured 4.22 light years (+/- 0.01).

 

At further distances I agree with YT. We know that certain elements of compounds give out a very specific colour light (the study of which is known as spectroscopy). And combining this knowledge with our knowledge of red (or blue) shifting (aka the Doppler Effect) we can calculate the relative velocities between distant objects. I don't know how the relative velocities can be used for distances, but I think it can.

 

Also Hertzsprung-Russell diagrams can be used:

http://en.wikipedia.org/wiki/Hertzsprung-Russell_diagram

 

 

[edit]some of my post is similar to m4rc's which was not there when I started typing this response

[Sashatheman]

thanks people. i also was reading up , that NASA is gonna send some probe i think in 2011, that can measure star distances using parralax, to a much more accurate degree, and will give us better proof

[chemfreak]

A.U's wich ar astronomacal units. Basicly the distance from the Earth(us) to the sun(big hot firery thingy that gives us light)

[[Tycho?]]

A.U's wich ar astronomacal units. Basicly the distance from the Earth(us) to the sun(big hot firery thingy that gives us light)

 

AUs are used for distances within a solar system. They are far too small for the distance between stars and galaxies. For such distances light years or parsecs are used. You can look them up on wikipedia to find out what they are.