• Question: When Red-Shift and Hubble's Law were being discovered, how did the scientists know how far away the stars they were observing were?

    Asked by bolzanoweierstrass to James, Marcus, Martin, Rob, Suzanne on 19 Mar 2012.
    • Photo: Suzanne McEndoo

      Suzanne McEndoo answered on 19 Mar 2012:

      I think you can measure interstellar distances using parallax, so by seeing how far something moved when you change the position you’re looking from. Like how if you move your head, a tree in the middle distance will move more than the mountains behind it. They’re not easy measurements to make, when you’re talking about star distances, but people used this method as far back as the 1830’s.

    • Photo: Robert Thompson

      Robert Thompson answered on 20 Mar 2012:

      There are quite a few ways of telling the distance to stars. As Suzanne says Paralax is a good one. Because the earth rotates you can make a big trangle, measuring the angle between yourself and the star on both side of the earth and then work out how far away the star is. I’ve got some notes at home of other ways of doing it. I’ll have a look tonight.

    • Photo: Marcus Gallagher-Jones

      Marcus Gallagher-Jones answered on 21 Mar 2012:

      Aside from the parallax, which is good for distance of about 400 light years, method I’ve read about another one. The brightness of a star is directly related to it’s colour spectrum. Measuring a distant stars colour spectrum is a bit more straightforward than its brightness. They can then use this measurement to calculate the brightness of the star. The stars brightness can then be compared to those of nearby stars with well characterised distances. There is a proportional relationship between brightness and distance and so the distance can be inferred from these measurements.

Comments