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Measuring distance from stars

  1. Mar 2, 2005 #1
    The distance between stars is measured by the time it takes light to travel between them correct? How do you measure the time it takes?

    for example from CNN "It is 12.7 billion light-years away, meaning the light just recorded -- by NASA's Chandra X-ray Observatory -- took 12.7 billion years to reach the vicinity of Earth."
    How do they figure out how long it took this light to reach us?
  2. jcsd
  3. Mar 2, 2005 #2


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    Actually, there are a lot of different methods used to determine the distance to stars, galaxies, etc. The most basic (and most reliable) way for stars is parallax. For more discussion on that, see here. That only works for relatively nearby objects, however.

    Well, it would depend on the object they're talking about, but at that distance, they probably have approximated the distance (and, thus, the light travel time) based on the redshift (and http://www.absoluteastronomy.com/encyclopedia/H/Hu/Hubbles_law.htm [Broken]). Of course, the process going into determining the cosmological parameters needed to do that calculation is quite complicated, but that's the basic idea.
    Last edited by a moderator: May 1, 2017
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