Ok so how is it scientist's know?

Question

I've always wondered about this .. heres an example ... they say stuff like .. the ding bat gallaxy is 18 gazillion miles from earth! .... how is it they know it's that far for sure? since they've never been there ..is there some type of measure or somethin' they use or are they just makin' a wild guess? ; )

wow kbw3! naturally some of that was way over my head .. but the way you explained it .. I was able to understand it ... I think! lol thank you for a wonderfully informative answer! if your not a science teacher .. you should be! ; )

omg mike! thats a really sweet thing ta say ... i'm all red in the face now babe! ; )

Answer 1

There are three methods for determining distances. For the closer stars, they use heliocentric parallax. That is taking an angular measurement of the star at opposite sides of the earth's orbit. This baseline of 186 million miles allows them to use trigonometry to make reasonable estimates to stars within a couple hundred light years. But these will be limited to our own corner of this galaxy.

For more distant stars, they use certain kind of variable stars as cosmic yardsticks. These are the RR Lyrae and Cepheid variables. These are large, bright stars which have periods of varying brightness which are proportional to their brightness. They are identified by their spectroscopic features and verified by population studies. One star would not be enough to be confident, but thousands logged and analyzed lead to reliable conclusions about their distances, as a class. Some of these stars are bright enough that we can see them in other galaxies. That way, we can know with fairly reasonable accuracy, the distances to the nearer galaxies. If Andromeda, for example, had only one, we would have to allow a large margin of error, but when a hundred of them all indicate the same distance, then the measurement is quite reliable.

For distant galaxies, we can't resolve individual stars, so the only way we have to estimate is by looking at their red shift. In general, the farther away an object is, the faster it is receding from us. This is not an absolutely reliable method, but along with comparing the type of galaxy with the size that type usually is, gives a fairly dependable measure. Red shift is observed in the spectra of galaxies and seeing how far the emission features are displaced for common elements.

This kind of science represents human intelligence and persistence at its very best.

One more thing: stars in our own galaxy are at vastly different distances from us but their speeds are not so different. We can tell how fast a star is moving toward us or away from us. And the closer stars will generally show greater degrees of motion than the more distant ones. So knowing these two things, we can come up with at least ball park estimates of the distances to stars that are too far away for parallax measurement. Imagine a huge flock of birds that ranges from a few yards distant to a mile. Suppose you know only their locations and apparent speeds but not their sizes. You can see how you can come up with fair estimates of their speeds, even if some are traveling faster or slower than the average.

Eelfins, yes, Cepheid variables, as I mentioned. But only for a few of the closer galaxies.

Answer 2

First of all there are ways of measuring distances that change in a permanent moving universe. Scientists can only find out was their tools experiments and knowledge allows them to find at a moment in time. This can change with another scientist's claim and so on. In other words scientific knowledge can be updated or eventually confirmed by a fully justified event or discovery that science itself will acknowledge as proof beyond doubt.

Answer 3

I don't know about all that sweetie, but I do know there's one particular ding bat I honest to God wish was so much closer to me. ;)

Answer 4

Cepheid variables is the correct answer