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max8166
2006-Aug-17, 10:19 AM
I know the moon circles the earth every 29.5 days, and that it has an eliptical orbit, but how can I find out where it will be? Does it follow the equator in its orbit? The sun has a solstice as the axis of the earth changes over a year but does the moon have a solstice too?

Is the information in here http://en.wikipedia.org/wiki/Moon ?
And Here http://en.wikipedia.org/wiki/Ecliptic#Ecliptic_and_Moon ?

trinitree88
2006-Aug-17, 11:04 AM
I know the moon circles the earth every 29.5 days, and that it has an eliptical orbit, but how can I find out where it will be? Does it follow the equator in its orbit? The sun has a solstice as the axis of the earth changes over a year but does the moon have a solstice too?

max. If you sat on the same rock every sunrise, moonrise....the sun, moon, and the planets follow nearly the same path across the sky. If it was exact, there'd be an eclipse every month. It's approximate, so it isn't a line, but a band in the sky.. This band is divided into 12 sections. At sunrise, the sun appears to rise while in a constellation, that's the zodiacal "sun sign". 12 of them cover the year...hence, the signs of the zodiac.
When teaching the night sky, I sit a kid in a chair, facing ~ South, and have them follow the sweep of a laser pointer across the wall...motion of the sun. Successive sweeps rise slightly from Dec.21-June 21...drop slightly from June 21-Dec.21
If you pay attention to the daily sweeps, you should find the moon ~there at night, and the planets, too. You can naked eye see Mercury, Venus, Mars, Jupiter, Saturn (Earth)....This is the simplified version. Pete

gwiz
2006-Aug-17, 11:17 AM
Most astronomy magazines publish monthly charts of where things are, including the moon. No doubt there are websites that do the same - suggest you google a bit - the word "ephemeris" might help.

cjbirch
2006-Aug-17, 11:23 AM
This website should help you find what your looking for!
http://www.fourmilab.ch/yoursky/

grant hutchison
2006-Aug-17, 12:21 PM
The moon's orbit is inclined by about 5 degrees relative to the ecliptic plane. (The ecliptic plane follows the zodiacal band in the sky that trinitree88 described above.) The orbit twists around slowly in the ecliptic plane, maintaining a more or less constant tilt.
Within its orbital plane, the moon moves closer to the Earth (perigee) and farther from the Earth (apogee) at either end of its orbital ellipse. These points also migrate continuously around the orbital plane.
So its position in the sky is difficult to predict without some maths, and impossible to predict accurately without a lot of maths.
Websites or astronomy software are by far the easiest ways to find the moon's position.

Grant Hutchison

max8166
2006-Aug-17, 12:42 PM
Oh this is good, this is just what I was looking for thanks
http://www.fourmilab.ch/earthview/moon_ap_per.html

Blue Fire
2006-Aug-17, 02:36 PM
From: http://www.astro.wisc.edu/~dolan/constellations/extra/Zodiac.html

The Zodiac is the ring of constellations that the Sun seems to pass through each year as the Earth orbits around it. Contrary to popular belief, there are actually 13 zodiacal constellations, if you pay attention to the way astronomers define them. In addition to
Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, and Sagittarius,
the Sun also passes through
Ophiuchus.
The bold is mine. Just thought I'd put my 2 cents in for the sake of being contrary. ;)

grant hutchison
2006-Aug-17, 02:57 PM
Contrary to popular belief, there are actually 13 zodiacal constellations, if you pay attention to the way astronomers define them. The twelve astrological "houses" familiar from newspaper horoscopes span 30 degrees each, so violate all the zodiacal constellation boundaries. Two of the houses (Scorpio and Capricorn) don't even have the same names as their parent constellations. The houses have also shifted relative to the background stars in the last few millennia, so that the astrological house of Ares is sitting in the constellation Pisces, and so on around the sky.

Grant Hutchison

hhEb09'1
2006-Aug-17, 10:27 PM
I know the moon circles the earth every 29.5 days, It actually circles the earth in a little over 27 days--so that it goes through the cycle of constellations in those 27 days.


This band is divided into 12 sections. At sunrise, the sun appears to rise while in a constellation, that's the zodiacal "sun sign". 12 of them cover the year...hence, the signs of the zodiac.As grant hutchison mentions, astronomers use a different definition of the constellations than the astrologers do, but even then, the signs have shifted more than a whole sign because of precession so that the sun does appear in the current sun sign.
When teaching the night sky, I sit a kid in a chair, facing ~ South, and have them follow the sweep of a laser pointer across the wall...motion of the sun. Successive sweeps rise slightly from Dec.21-June 21...drop slightly from June 21-Dec.21
If you pay attention to the daily sweeps, you should find the moon ~there at night, and the planets, too.The difference in the height of the sun will vary as much as 47 degrees from early summer to early winter, but when the ecliptic is high in the day, it is low at night, so the height of the sun at local noon on the first day of summer can be 47 degrees higher than the height the moon or planets attain that night.

max8166
2006-Aug-18, 08:50 AM
It actually circles the earth in a little over 27 days--so that it goes through the cycle of constellations in those 27 days.

Yes this is confusing me. On one hand we have:
Revolution period(Sidereal period)=27.32166155 days (27 d 7 h 43.2 min)
and on the other:
Synodic period = 29.530 588 days (29 d 12 h 44.0 min)

Any explaination would be gratefully received

hhEb09'1
2006-Aug-18, 09:25 AM
Yes this is confusing me. On one hand we have:
Revolution period(Sidereal period)=27.32166155 days (27 d 7 h 43.2 min)
and on the other:
Synodic period = 29.530 588 days (29 d 12 h 44.0 min)

Any explaination would be gratefully receivedThe 29.5 days is the time between full moons, more or less. Since the earth and moon are revolving about the sun, the moon takes a couple more days to "catch up" to the point where it can be full again.

Similarly, the earth rotates in 23h 56m--it takes an additional 4 minutes to "catch up". If you add up those four minutes per day, over the entire year, you find that there is an additional day/rotation that is "lost" because of the revolution about the sun. Those extra couple days in the case of the moon add up to one full "lost" revolution.

max8166
2006-Aug-18, 10:07 AM
So to position the moon in the longitudinal sense, in other words ignoring the latitude. Can I say that for every earth day (24 hours) the moon moves about 13.179 degrees ** in the sky? (just in the longitude plane)

** 360/27.32166155

grant hutchison
2006-Aug-18, 10:58 AM
So to position the moon in the longitudinal sense, in other words ignoring the latitude. Can I say that for every earth day (24 hours) the moon moves about 13.179 degrees ** in the sky? (just in the longitude plane)
Afraid not.
1) Because the moon has an elliptical orbit, it moves alternately faster and slower across the sky.
2) When the moon is far from the celestial equator, it will cross more lines of celestial longitude for a given angular movement than it does when it's near the equator: the lines of longitude are closer together (as they converge towards the pole), and the moon is moving more nearly orthogonal to them.

Grant Hutchison

max8166
2006-Aug-18, 03:19 PM
13.179 degrees, I meant just as an approximation, how many degrees would I be out by in the worst case? I was only trying to approximate. Also as the moon crosses the Ecliptic twice an orbit or is it twice a month, can you approximate the Latitude by making it equal to the latitude of the sun (plus or minus 5 degrees)

grant hutchison
2006-Aug-18, 04:31 PM
13.179 degrees, I meant just as an approximation, how many degrees would I be out by in the worst case? I was only trying to approximate.Approximate to a thousandth of a degree? ;).
I don't know the size of the error, and of course the calculations to determine that are almost as complicated as the calculations to get an exact position for the moon. But I'd guess on the order of a few degrees.


Also as the moon crosses the Ecliptic twice an orbit or is it twice a month, can you approximate the Latitude by making it equal to the latitude of the sun (plus or minus 5 degrees)Again, afraid not. While the new moon will have the same approximate latitude as the sun, the full moon will have approximately the opposite latitude: south of the equator if the sun is north, north of the equator if the sun is south. Other phases will have intermediate latitudes.

Grant Hutchison

Lord Jubjub
2006-Aug-18, 11:51 PM
The moon is October and November is very low in the northern sky. So low that from Europe or Canada, it never completely achieves whiteness. The full moon at its height is still somewhat orange.

Or so I've heard. I've never had the chance to see the Hunter or Harvest Moon from that far north.

hhEb09'1
2006-Aug-19, 01:10 AM
The moon is October and November is very low in the northern sky. So low that from Europe or Canada, it never completely achieves whiteness. The full moon at its height is still somewhat orange.

Or so I've heard. I've never had the chance to see the Hunter or Harvest Moon from that far north.Not sure what you mean here. The moon tends to be higher then.

My astronomy software says that on Nov. 5, 2006, at 23h UT, from Paris, the moon will be at a height of 57 degrees.

max8166
2006-Aug-19, 09:32 AM
Taking a step back and looking at it another way, can I locate the moon if I know where the Ecliptic Plane is and then locate the moon on this plane preceding the sun by an approx cumulative 13.178 degrees per day, with a 5 degree oscilation about the ecliptic (with an oscilation period of half a rotation)?

hhEb09'1
2006-Aug-19, 01:18 PM
Taking a step back and looking at it another way, can I locate the moon if I know where the Ecliptic Plane is and then locate the moon on this plane preceding the sun by an approx cumulative 13.178 degrees per day, with a 5 degree oscilation about the ecliptic (with an oscilation period of half a rotation)?Um, yes, but I'm not sure what you mean by "preceding the sun". I think you mean, starting with a known position, the moon will advance through the approximate region of the ecliptic at roughly 13 degrees per day. It won't be exact, but it'll get you in the ballpark, unless you try to use it for predictions over very long periods of time.

Kaptain K
2006-Aug-20, 12:47 AM
The moon is October and November is very low in the northern sky.
You've got it backward. In the winter, the full Moon is very high in the sky. Just the opposite of the Sun.

Lord Jubjub
2006-Aug-20, 10:55 PM
Oops, well. . .having lived nearly all of my life south of the 40th parallel, the moon has never seemed to exhibit to me a noticeable shift in the sky.

hhEb09'1
2006-Aug-21, 01:16 PM
Oops, well. . .having lived nearly all of my life south of the 40th parallel, the moon has never seemed to exhibit to me a noticeable shift in the sky.Has the sun? :)

max8166
2006-Aug-26, 08:34 PM
On this page http://www.astronomynotes.com/nakedeye/s12.htm
I found this,
Moon drifts eastward with respect to the background stars (or it lags behind the stars). It returns to the same position with respect to the background stars every 27.323 days.
SO... where I said earlier that the moon:"preceding the sun by an approx cumulative 13.178 degrees per day" I think I meant the other way around :-
the sun is preceding the moon by an approx cumulative 13.178 degrees per day

hhEb09'1
2006-Aug-26, 08:56 PM
On this page http://www.astronomynotes.com/nakedeye/s12.htm
I found this,
SO... where I said earlier that the moon:"preceding the sun by an approx cumulative 13.178 degrees per day" I think I meant the other way around :-
the sun is preceding the moon by an approx cumulative 13.178 degrees per dayNo, you were right the first time. The sun moves through the ecliptic at about a degree per day in the same direction that the moon moves through at about that 13 degrees.

Although I wasn't sure earlier what you meant by preceding the sun.

max8166
2006-Aug-27, 09:48 AM
So does the moon orbit in the same direction as the rotation of the earth or in the counter direction?

cjbirch
2006-Aug-27, 10:16 AM
So does the moon orbit in the same direction as the rotation of the earth or in the counter direction?


When viewed from Earth's North Pole, the Earth and Moon rotate counter-clockwise about their axes. The Moon orbits Earth counter-clockwise and Earth orbits the Sun counter-clockwise.