lunar cycles
Apr. 27th, 2003 01:05 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
chrisvenusI have spent a long time tonight thinking about lunar cycles due to some evil woman making me *glares at ![[livejournal.com profile]](https://www.dreamwidth.org/img/external/lj-userinfo.gif)
nevecat*.
The original problem for me (and I think she was doing the same) was to create something that given a date and time would give you a phase of the moon. This was to be used for garou related purposes where the phase of the moon you are born under is relevant.
Now, for the last four hours or so I have been banging away at writing a nice web page to do this (makes it universally useful that way) and that was the easy part. The thing that has caused me much confusion and consternation is this. The data that I can find on the web for when full moons are generally don't have the same period between full moons.
Now my thinking is that the time between two full moons should be identical. It is based on a few things... The rotation of the earth around the sun, the rotation of the earth around its axis and the rotation of the moon around the earth. However, these are all regular very predictable things. The lengths of these are all constant to the best of my knowledge.
The first two clearly are, the only one that might not be (and this is the relevant one) is the moon but the only thing I can think that might alter that is gravitational effects from the sun distorting its orbit time but I am as sure as I can be without doing the maths that they are irrelevant. Or, as has just been pointed out elliptic orbits might make a difference, I believe that according to kepler's law or some such thing that the angular velocity is not constant so could that make a difference? Maybe if it is an elliptic orbit that is slowly progressing or something.
Anyway, the upshot of it is that this is driving me absolutely skatty. I have found no useful resources on the web that explain how to calculate when full moons happen and so on.
In the 30 minutes since I started writing this I have found http://www.peter-hayes.freeserve.co.uk/sun_moon.html which is a web page citing a book as a source of its calculations and the calcs are really quite complicated looking. They may be precise but at this stage I am too tired to work out what they mean. The fact it starts with 11 arrays, each of 60 elements makes me think it might be quite complicated.
Oh well, I'll look at it tomorrow. Meanwhile if anybody can find online resources explaining nicely about this that'd be great. Alternatively if anybody has decent books that might explain it then that too would be great.
But now I really *should* go to bed. Am tired now and need to be up and ready to leave the house in 8 hours. This really means I should be awake before that.
Oh well, at least now I can sleep on it and might have the answers I want in the morning. Not the usual way to get answers by sleeping on a problem but I'm a 21st century boy.
nevecat*.The original problem for me (and I think she was doing the same) was to create something that given a date and time would give you a phase of the moon. This was to be used for garou related purposes where the phase of the moon you are born under is relevant.
Now, for the last four hours or so I have been banging away at writing a nice web page to do this (makes it universally useful that way) and that was the easy part. The thing that has caused me much confusion and consternation is this. The data that I can find on the web for when full moons are generally don't have the same period between full moons.
Now my thinking is that the time between two full moons should be identical. It is based on a few things... The rotation of the earth around the sun, the rotation of the earth around its axis and the rotation of the moon around the earth. However, these are all regular very predictable things. The lengths of these are all constant to the best of my knowledge.
The first two clearly are, the only one that might not be (and this is the relevant one) is the moon but the only thing I can think that might alter that is gravitational effects from the sun distorting its orbit time but I am as sure as I can be without doing the maths that they are irrelevant. Or, as has just been pointed out elliptic orbits might make a difference, I believe that according to kepler's law or some such thing that the angular velocity is not constant so could that make a difference? Maybe if it is an elliptic orbit that is slowly progressing or something.
Anyway, the upshot of it is that this is driving me absolutely skatty. I have found no useful resources on the web that explain how to calculate when full moons happen and so on.
In the 30 minutes since I started writing this I have found http://www.peter-hayes.freeserve.co.uk/sun_moon.html which is a web page citing a book as a source of its calculations and the calcs are really quite complicated looking. They may be precise but at this stage I am too tired to work out what they mean. The fact it starts with 11 arrays, each of 60 elements makes me think it might be quite complicated.
Oh well, I'll look at it tomorrow. Meanwhile if anybody can find online resources explaining nicely about this that'd be great. Alternatively if anybody has decent books that might explain it then that too would be great.
But now I really *should* go to bed. Am tired now and need to be up and ready to leave the house in 8 hours. This really means I should be awake before that.
Oh well, at least now I can sleep on it and might have the answers I want in the morning. Not the usual way to get answers by sleeping on a problem but I'm a 21st century boy.
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(no subject)
Date: 2003-04-27 04:16 am (UTC)A day isn't really a day... it is measured by the time it takes the sun to travel around the earth and back to the same point, however it doesn't take into account the rotation of the earth around the sun.
roughly the same thing happens with the moon... every day the moon is 17 minutes later than it should be, or something...
add into that that the earths orbit around the sun is elliptical, days are 24hours and 17mins long, we are tilted on an axis, the sun is believed to be orbiting too and everything gets a little complicated...
brought to you courtesy of Astronomy 1Ch...
(no subject)
Date: 2003-04-27 05:45 am (UTC)Hrm.
Don't suppose you know anything about Julian Dates do you? Since those were alo given, and if they're 'accurate', they might be more useful...
Small enough to fit on your phone...
Date: 2003-04-28 04:58 am (UTC)http://www.piecafe.demon.co.uk/
Fits on my phone, which makes those midgames calls so
much easier.