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Sidereal vs. Solar Day

  1. Oct 8, 2005 #1
    Imagine you go out tonight at 9:00pm and see a star rising on the horizon. If you go out tomorrow at the same time, the star will be in a different location. What day would you be able to see the same star rise from the horizon at 10:40pm?

    My half-answer:
    The difference between a sidereal and a solar day is that the solar day is ~3.9 min longer.

    However, I cannot seem to apply this concept to figure out which day the star would rise at 10:40pm.

    I have formulated my own equation,

    tn = to - 3.9n

    Where tn is the final value of time (in this case, 10:40pm), and to is the original value of time (in this case, 9:00pm). n is the number of days (in this case, what we are trying to find).

    By substituting values into my equation, I get:
    n = (9:00pm - 10:40pm) / 3.9 min

    However, I cannot figure out the answer from that. This is a very easy question but I am really stumped. Any help?
  2. jcsd
  3. Oct 8, 2005 #2
    How many minutes from 9:00pm to 10:00pm and then how many more from 10:00pm to 10:40pm?
  4. Oct 8, 2005 #3
    9 -> 10 = 60 min
    10 -> 10:40 = 40 min

    100 min in total

    Then what?

    Is it :

    100 min / 3.9 min = 25.6
  5. Oct 8, 2005 #4
  6. Oct 8, 2005 #5
    I cannot believe I am still confused.....


    but 25.6 what?

    days? How does that work according to units?
  7. Oct 8, 2005 #6
    or how about instead of 100 min.... 1440 min - 100 min = 1340 min

    1340 / 3.9 = 343.6 days?
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