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Pooh-Bah
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Pooh-Bah
Joined: Jan 2001
Posts: 1,819 |
In reply to:
One of the things I am most grateful for living at just this time on earth is that the full moon rises just at dusk and is up in the sky the entire night long. I think that is amazing, astoundingly beautiful, and inspiringly mystical. But surely, there have been whole epochs on earth when this was not the case, when the full moon rose during the day, and was on the other side of the earth during the night.
I do not believe that that is possible. As stated earlier, the moon is full when its orbit about the earth places it directly away from the earth. (More clearly, the earth is right between the moon and sun.) Thus lunar eclipses can only occur on a full moon and solar eclipses can only occur on a new moon, on those occasions when the moon's orbit is in the same plane as the earth's and the sun's. The full moon will always rise at about sunset and set around sunrise because of the orientation that makes it full in the first place. The exact time will vary depending on the observer's distance from the equator. The corollary to this is that crescent moons will be visible at different points during the daytime.
What I find scientifically mind-boggling about the moon is that its rotation is such that we always see the same face of it. This seems to me to be an extraordinary coincidence, and I would love to hear more on the subject from anyone more learned in astronomy.
The spell checker suggests replacing moon's with mooned.
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Posts: 77
journeyman
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journeyman
Joined: Nov 2002
Posts: 77 |
Well, I don't profess to have a logical mind. So I guess I'll have to ponder just what it means to me now if indeed the full moon always rises at dusk (depending more or less upon one's relation to the equator), and sets sometime around dawn, throughout all history. That's almost *more beautiful in its symmetry. Quite remarkable really. Is it true?
And how useful to have been able to count on the bright glow of the full moon to carry out all those ancient rites in the middle of the night!
And this spell checker is the most ridiculous thing I have ever come upon. Utterly useless, which is too bad as my spelling needs work!
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Joined: Jan 2001
Posts: 1,819
Pooh-Bah
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Pooh-Bah
Joined: Jan 2001
Posts: 1,819 |
Well picture the half moon. At half moon, the moon is at right angles from the line connecting the sun and the earth. The light from the sun is hitting the moon, and from our vantage on earth, it looks like a tennis ball lit up from one side with a flashlight. Thus we see what appears to be a half disc. At full moon, it like we have our backs to someone who is holding a flashlight, and we're facing a tennis ball (which is a little higher than our heads so it isn't eclipsed by our shadow) and it is illuminated by the flashlight. We see the whole face of the tennis ball that is illuminated.
So if at full moon, the earth is between the sun and moon, then during the day you're on the part of the earth that is facing away from the moon. As the earth continues to rotate, the moon appears at one horizon, while at the time the sun is disappearing over the other horizon.
Gibbous moons occur as the moon is beyond the earth (from the sun) but not quite 180 degrees. Crescent moons occur when the moon is nearer to the sun than the earth.
This phenomenon is related to the way that we can only see Venus in the morning or evening. Venus's orbit is inside the earth's orbit, so at night when our part of the planet is poitning away from the sun, we're also pointing away from wherever Venus might be. But sometimes in the mornings or evenings, Venus can be seen low in the sky brightly reflecting the light of the sun.
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Posts: 2,636
Carpal Tunnel
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Carpal Tunnel
Joined: Jun 2001
Posts: 2,636 |
MM, Ænigma, our spellchecker, is ridiculous and frustrating only if you want it to function normally. That would soooo not fit in with the rest of this board. Have fun with it and use your RL dictionary to check spellings.....or better yet, spell however pleases you. That werks for us, right musick? 
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Pooh-Bah
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Pooh-Bah
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Posts: 872
old hand
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OP
old hand
Joined: Sep 2001
Posts: 872 |
What I find scientifically mind-boggling about the moon is that its rotation is such that we always see the same face of it. This seems to me to be an extraordinary coincidence...
Thats an easy one Alex, *the tidal pull of the earth through time has slowed the moons rotation around its axis to match the moon's orbital period, so that it has zero rotational momentum relative to the earth.
But the moon pulls back, and acts as a brake on the eastward spinning earth. Geologic findings (one the Pottsville Formation in Northern Alabama) indicate that 900 million years ago, a day on the then fast spinning earth, was only about 18 hours long.
But the same braking force was acting on the moon as well. And since the moon has only 1% of the mass of the earth, the moon "locked up" a long time ago and keeps the same side always facing the earth.
Then be it ours with steady mind to clasp
The purport of the skies-- the law behind
The wandering courses of the Sun and Moon.
________________________________________- Lucretius
* Adapted from Seeing in the Dark ~ Timothy Harris.
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Joined: Sep 2001
Posts: 6,296
Carpal Tunnel
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Carpal Tunnel
Joined: Sep 2001
Posts: 6,296 |
Remember our discussion a while back about the asteroid Cruithne? How we learned that its orbit is horseshoe-shaped?
I'd love to see the math on that.
I'd love to hear Copernicus's reaction to that math.
I've got here in my notes:
"Cruithne's path is much more complicated than simple satellite motion; pondering the diagrams carefully should help clarify matters....Hoseshoe orbits are named because of their shape in a reference frame which corotates with their accompanying planet, and have been known theoretically for many years. "
--Paul Wiegert, previously of the Dept. of Physics and Astonomy, York University, Toronto, Ontario
Point is: There aren't just elliptical orbits--or circular as Copernicus thought. The horseshoe one is the oddest one I know of. Any other unusual orbits we should know about?
AnnaS: I promise you two very good words tomorrow. I left my physics book at home.
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Posts: 77
journeyman
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journeyman
Joined: Nov 2002
Posts: 77 |
ok, ok. You guys are great! I'm so glad I found all of you. People who think! Imagine that...Poeple who love to think and want to learn.... green flashes, high altitude sprites, speleogenisis (well, I'm STILL waiting on that one).
It's all good.
Thanks, mm
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Joined: Jun 2002
Posts: 7,210
Carpal Tunnel
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Carpal Tunnel
Joined: Jun 2002
Posts: 7,210 |
The horseshoe one is the oddest one I know of. Any other unusual orbits we should know about?
I believe there are sun systems that have figure-8 orbits...
formerly known as etaoin...
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Joined: Nov 2002
Posts: 77
journeyman
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journeyman
Joined: Nov 2002
Posts: 77 |
My mother used to sing this song to us at the piano when we were children. She's from an irish family; grandpa was a union man who worked for the railroads, and they had the sign of the hobo on their house when she was a child, even though it was the depression and they didn't have enough food for the four little girls.
This song was beautiful, and I can hear the melody and sing the words in the memory of my mind. Thanks Juan, for taking me back to a gentler place and time in my life....
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