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    Jovian's Avatar
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    Default Homework Question - calculating the time of sunset on winter solstice



    Let me pre-face this by saying that I indeed have read the sticky on homework questions, and that it is ambiguous as to whether they are forbidden, discouraged, or discouraged under certain circumstances. The first case seems unlikely so I'm going to post this anyways. I know there are a few guys on here who could probably help me out, so here it goes. (I am going to copy and paste some of this from another forum)


    1. The problem statement, all variables and given/known data

    On the date of the winter solstice (Dec. 22), what are the approximate local sidereal times and local apparent solar times at sunset? (Assume 40 degree N latitude)

    2. Relevant equations

    Local apparent solar time = the HA (hour angle) of the sun as it appears in the sky + 12 hours

    Winter solstice = day of the longest night

    sidereal time = right ascension of an object on the upper meridian

    3. The attempt at a solution

    I know the solution must be related to the HA of the sun at sunset, but I really don't know how to figure out what that is... my textbook is awful so if anyone could get me started I'd appreciate it.

  2. #2
    DaveW's Avatar
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    Default

    Just remember that sin(Alt) = sin(Dec)*sin(Lat) + cos(HA)*cos(Dec)*cos(Lat). You have all but one of those, so go from there.
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  4. #3
    Jovian's Avatar
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    Quote Originally Posted by DaveW View Post
    Just remember that sin(Alt) = sin(Dec)*sin(Lat) + cos(HA)*cos(Dec)*cos(Lat). You have all but one of those, so go from there.
    Thanks for the equation, no where in my book was this given... I was able to find the local apparent solar time, hopefully I can now figure out how to get the sidereal time.

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    Default

    If you want to check results for any UK place, I made a rising and setting times calculator at sunset.dyndns-web.com
    I used the algorithm by the Nautical Almanac Office.

    Thanks!

 

 

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