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    Moonrise/Moonset
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    Journeyman Greytalker

    Joined: Sep 20, 2001
    Posts: 179


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    Mon May 14, 2018 5:04 pm  
    Moonrise/Moonset

    I confess that a lot of discussion involving Oerth's solar system and the calendar goes over my head.

    From what I can tell about the moons, their cycles are so regular that the same nights each year have full moons, half moons, or new moons, etc. That also suggests the times of moonrise and moonset are consistent from year to year.

    I want to create an adventure that takes place on the night of Growfest 4th (spring equinox). I want the adventure to begin with one of the moons rising, and conclude when that same moon sets.

    Does anyone have any information or learned guesswork on when moonrise and moonset would be that night?
    Adept Greytalker

    Joined: Apr 11, 2009
    Posts: 341
    From: Aspedri

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    Mon May 14, 2018 8:38 pm  

    Edmundscott,

    I was amusing myself writing a VBA almanac for Greyhawk, at one point, and moon rise and moon set times were extremely complicated if I remember correctly. A lot depends upon latitude. I ran out of energy to pursue this in the detail desired, and did not consult Greyspace which might have proven helpful. Short version, I made a series of very crude guides for storytelling, but not particularly helpful for high detail.

    During a full moon, the sun rises exactly 6 hours before midnight, and sets 6 hours after midnight. When the moon is waning, moonrise will occur less than 6 hours before midnight and moonset will occur more than 6 hours later, proportional to how far from a full moon the date is. The reverse occurs during a waxing moon, when it rises more than 6 hourse before midnight each night, and sets less than six hours after midnight. In all cases, I had the moons in the sky for 12 hours, shifting the rise and set times.

    This rule could use some revision, and does not account for latitude. Given time, I may revisit the approach for Luna... Celene might be more troublesome, even suspending Newtonian Mechanics. I recall that calculating e (elongation) had me giving up as it brought back bad memories of geometry and I was not attempting to earn a masters in astronomy at the time. That, and without a heliocentric model, it becomes nightmarish to contemplate the sun's position.

    This may also help:

    https://www.almanac.com/content/when-will-moon-rise-tonight
    Journeyman Greytalker

    Joined: Sep 20, 2001
    Posts: 179


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    Tue May 15, 2018 3:36 pm  

    In your second paragraph, where you say "sun" you mean "moon" right?

    Why would Celene suspend Newtonian mechanics? Wouldn't it just have a longer orbit?

    I just checked Weather Forecaster for Greyhawk's World, and saw that Luna will be at 1/4 on Growfest 4 and Celene will be full, so I'll use Celene's rise and set as the bookends of the adventure.

    The latitude will be 27 degrees N (southwest Sterich) and sunrise at 5:34am and sunset 5:49pm. If your link holds true for Celene, then I think we can set moonrise and moonset around those times (or split the difference and say 5:41am & pm).

    Thanks for the thoughts and the link!
    Adept Greytalker

    Joined: Apr 11, 2009
    Posts: 341
    From: Aspedri

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    Wed May 16, 2018 8:34 pm  

    Curses! You are correct, I meant sun.

    You are also correct that a second body would not alter Newtonian Mechanics... but it would make the math a lot harder...
    Master Greytalker

    Joined: Nov 01, 2007
    Posts: 691
    From: NOW IN Cape May, NJ! Loving the new digs!

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    Fri May 18, 2018 12:53 pm  

    And interesting and informative thread!
    Wow, thanks for that!!

    Also Tarrelton
    edmundscott wrote:
    In your second paragraph, where you say "sun" you mean "moon" right?
    tarelton wrote:
    Curses! You are correct, I meant sun.
    Did you still mean moon, rather than sun again, right?
    Razz
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    Apprentice Greytalker

    Joined: Dec 01, 2006
    Posts: 33


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    Sat Jun 16, 2018 5:31 am  
    Re: Moonrise/Moonset

    edmundscott wrote:
    I confess that a lot of discussion involving Oerth's solar system and the calendar goes over my head.

    From what I can tell about the moons, their cycles are so regular that the same nights each year have full moons, half moons, or new moons, etc. That also suggests the times of moonrise and moonset are consistent from year to year.

    I want to create an adventure that takes place on the night of Growfest 4th (spring equinox). I want the adventure to begin with one of the moons rising, and conclude when that same moon sets.

    Does anyone have any information or learned guesswork on when moonrise and moonset would be that night?

    A full moon rises at sunset and sets at sunrise. A new moon is opposite, a first quarter moon rises at noon and sets at midnight, and third quarter rises at midnight and sets at noon.
    Exact time will vary somewhat with daylight savings time/where you are in the local time zone, local topography, etc.
    And of course the time of sunset/rise will depend on your latitude.
    But to keep things simple, assuming you are at the equator, the sun rises and sets at 6am/pm
    If you have a calendar of the moon phases, its just a math calculation to find the exact setting/rising of a moon in comparison to its closest quarter.

    Take the lunar cycle and divide that into the hours in a day, and that's how much later the moon will rise each day. Which for Earth, its 24/28, which is .85 hours, or about 51 minutes.

    So Celene, with a cycle of 91 days, would rise/set about .26 hours, or 16 minutes later each day. (Assuming Oerth has a 24hr day).
    So 5 days after the fullmoon of Celene, it will rise an hour and 20 minutes after sunset (16minutes x 5=80 minutes). Which will be 7:20pm at the equator, or anywhere during the equinoxes. If you want the exact local time, based on time of year and latitude, ill let someone else work the math for that!
    Paladin

    Joined: Sep 07, 2011
    Posts: 831
    From: Houston Texas

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    Wed Jul 25, 2018 4:47 pm  

    Here is one persons approach to the moons and how they relate... I was questing for something else at the time so have not don the hard math on it.. but a cursory look is promising for those that like "crunchy bits"

    DLG
    https://www.nirgal.com/games/rpg/greyhawk/tides_math
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