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Homework Help: Science And PhYsics HW HELP!

  1. Mar 27, 2004 #1
    Hello everyone. I have a question and I'm not sure how to answer it.

    Q: Name the types of electromagnetic radiation that are used to obtain images of Earth from space. In each case include a concise description as well as the frequency or wavelength range.

    BTW, I think I'll probably be only using this thread each time I need help, so I hope that's okay with everybody!
  2. jcsd
  3. Mar 29, 2004 #2


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    Well, I suppose one could put a big mirror in orbit, then look at it through a telescope and see an image of the earth in the mirror: that would be using light but i don't believe that's ever actually been done.

    The only way I can think of that electromagnetic radiation has been used to get images of the earth from space is by relaying bitmapped pictures by radio waves. Hmmm, do they use micro-waves for that now?
  4. Apr 5, 2004 #3
    Question: The nearest star, Alpha Centauri A, is 4.07 x 10^16 m from Earth.

    a. How many light years is it away from Earth?
    b. What is the advantage of stating stellar distance in light years rather than meters?

    Part A, I got stuck because I don't know wheither to use the distance from the star to Earth, or the 9.46 x 10^15 m which is the distance light can travel in 1 year.

    I'm not sure, but for Part A, I divided the distance from AC to Earth by the distance light travels in one year and got 4.30 light-years. I don't know if I did it right, so can someone check my solution?

    And I have no idea what this answer is:

    What is the advantage of stating stellar distance in light-years rather than meters?
    Last edited: Apr 5, 2004
  5. Apr 8, 2004 #4

    for B i wud assume its because in meters the distances are huge so to use them in light years tends to make it a bit easier to understand ..... (just a guess)

    and yes you should divide the distance between AC and Earth by the distance light travels in a year, but 4.3 light years sounds wrong m8 i believe closest star is 20 light years + away ..... not sure tho just my 2 cents
  6. Apr 9, 2004 #5
    That IS the answer. We never want to write really big or small numbers, because it's more work to write and it is more difficult to comprehend. A second reason to use lightyears is because it gives us the amount of time we are looking in history of the specific star.
  7. Apr 9, 2004 #6


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    And, yes, alpha centuari (strictly speaking proxima centauri is the star closest to earth- alpha centauri is actually a triple star system with "proxima" be the one of the three closest) is about 4.3 light years from earth- certainly not "20 light years"!
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