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Distance of stars

  1. Nov 12, 2003 #1
    please can somebody help me with this parallax equation:

    D=distance to star
    using the rule D=(d/2)/tan(theta/2)
    when d = 300*10tothe6
    and theta = 5*10tothe-5

    what is the distance to the star in km and light years?
  2. jcsd
  3. Nov 12, 2003 #2
    Okay - assuming that you've given the units in kilometres and degrees...

    To get the answers in km you should just be able to plug the numbers into a calculator.

    To get the answer in light years you have to first calculate how far a light year is (in km, obviously).

    Rather than me just giving you the answer, why don't you have a go, then we can see if our answers agree...

    Last edited: Nov 12, 2003
  4. Nov 12, 2003 #3
    hi there thankyou for your interest in my posting jess

    d is in km
    theta is in degrees
  5. Nov 12, 2003 #4
    You'll be wanting to hit 'post reply' rather than 'new thread', then :wink:

    Oooh look - we've been moved

    Last edited: Nov 12, 2003
  6. Nov 12, 2003 #5

    Tom Mattson

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    Presto! The threads are merged.
  7. Nov 12, 2003 #6
    for this answer i get a result of:


    So, is this answer the number of km?

    what is this answer in exponential form? ie: 34 * 10tothepower13?

    1 light year is 9.467*10tothepower12, so in light years i think the distance will be:
    27 light years

    Please let me know if i am right
  8. Nov 12, 2003 #7
    Yes, that's the answer in kilometres, and it's the same one that I've got.

    34 x 10^13 km is correct as well.

    If you take the speed of light to be 300,000 km/s, then a light year is 9.461 x 10^12 km - which looks roughly like what you put.

    I get an answer of 36.3 l.y though - you might have typed a digit wrong somewhere, perhaps. Even a back-of-the-envelope type calculation gives an answer of at least 34, if you look closely.

  9. Nov 12, 2003 #8

    thankyou very much jess!
    I need the help for some uni coursework.
    p.s. I am from edinburgh too!
  10. Nov 12, 2003 #9
    This isn't Astronomy 1Ah or 1Ch work, is it?
  11. Nov 12, 2003 #10
    i study at the university of abertay dundee and travel from edinburgh.
    My coursework is from "horizons of science 1".
    this module is concerned with the big bang, black holes, telecommunications and cosmological phenomena
  12. Nov 12, 2003 #11
    Hehe - for a moment there I thought you might be one of my tutees (if that's the right word)

    Good luck with the rest of your course...

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