Why am I halucinating the moon seems tobe in a different orbit? I'm 36 degrees North and the moon was allmost 90 degees to the earth Saturday morning.
Tom
Newbie
Moon's Orbit
Why am I halucinating the moon seems tobe in a different orbit? I'm 36 degrees North and the moon was allmost 90 degees to the earth Saturday morning.
Tom
Order of Kilopi
welcome to the boards Tom!
I assure you that the moon did not change orbit, although I do not know why you saw such a thing, I will leave it to a professional to figure it out.
(Calling KenG, your needed in the Moon's orbit thread)
Member
Newbie
Thanks for the reply. For the last 3 or 4 days the moon has been rising in the NE, and setting in the NW. Is this its normal path? It was overcast last nite, so I could not see it. I'm in NE Oklahoma. Whats the difference between a Junior Member and a Senior Member?
Order of Kilopi
It is a rating according to the amount of posts you have.
I think Junior is <50, Plain Member is 50-99, and Senior is 100+
I might be wrong about the Junior to plain Member part, It might start at 40 for the plain member, but I am pretty sure it starts at 50.
I was misinformed on the moons orbit, my apologies, My general science teacher always said it was fixed in unchanging orbitI wonder if it has more to do with the earths tilt then the moon actually changing position?
Order of Kilopi
Coincidentally, someone last year, this time, thought the moon was directly overhead. See topic moon directly overhead, manchester
From table generated at US Naval Observatory Sun/Moon Altitude/Azimuth Table:
It looks like at around 2:45 AM, people in your region saw the moon at almost 80 degrees up from the southern horizon -- if I entered your location and time right.Code:W 98 00, N36 00 Altitude and Azimuth of the Moon Dec 18, 2005 Central Standard Time Altitude Azimuth Fraction (E of N) Illuminated 02:30 78.8 162.8 0.93 02:40 79.2 174.2 0.93 02:50 79.2 186.1 0.93 03:00 78.8 197.5 0.93 03:10 78.0 207.8 0.93 03:20 76.9 216.7 0.93 03:30 75.6 224.3 0.93
Edit: And for the bonus question...
Just as predicted, same table:Originally Posted by twa47
It set around 10:15 AM, about 300 degrees east of north (i.e. 30 degrees north of due west).Code:[Moonset] 10:10 0.8 299.8 0.91 10:20 -1.4 301.2 0.91 [Moonrise] 20:00 -2.0 60.0 0.89 20:10 0.2 61.4 0.89
It rose around 8:05 PM, about 60 degrees east of north (i.e. 30 degrees north of due east).
Roughly, the winter night moon follows a similar path to the summer day sun.
Order of Kilopi
Yep, the Moon's doing what it should be doing - rising in the NE, setting in the NW.
Round about the time of the full Moon, the Moon is on the opposite side of the sky from the Sun.
In winter, the Sun is low in the southern sky from where you are, rising in the SE and setting in the SW, giving short days. That puts the full Moon high in the sky, so it rises north of east and sets north of west.
In summer, the situation is reversed: the Sun rises in the NE, climbs high in the southern sky at noon and sets in the NW, giving you long days; but the full Moon is low in the southern sky, rising in the SE, setting in the SW.
The situation is compounded at present because the tilt of the Moon's orbit has carried it north of the ecliptic while it's passing through full phase, so it's rising even higher in the southern sky than usual, carrying it well north of west before it sets, and well north of east when it rises.
Grant Hutchison
Order of Kilopi
I think what was confusing you, twa47 (yes, welcome), is the term "unchanging orbit". This means the orbital plane of the Moon doesn't change (at least not in a human lifetime) from the point of view of distant stars "looking in" on our solar system. This is the most objective frame to use, called the "sidereal frame". But from our perspective in our back yards here on Earth, the path taken by the Moon through the sky as the Earth rotates is complicated by the Earth's orbit around the Sun. The orbit means that the Moon's phase is different when the Moon is seen against the same background stars as the year goes by (think about it-- the Sun would be seen against different zodiacal constellations, so when the Moon is in front of the same stars, the Sun is in front of different ones, so the phase is different). Thus if you match up different phases throughout the year, you can get the Moon to follow the same apparent path, but if you pick the same phase, like the Full Moon in Grant's post, then it will follow a different apparent path across the sky in different seasons.
Order of Kilopi
Ken, you were 2hrs and 8min late
Member
Order of Kilopi
You're right Dragon Star! You have to move fast around here...
Established Member
The Moon
Last night (Dec 17, 2005), the maximum elevation of the moon, as seen from Tulsa, Oklahoma was about 81 degrees, at 1:40 AM CST. This morning the moon transited about 2:40 AM CST, at an elevation about 79 degrees. Tomorrow it will transit about 3:30 AM CST, at about 76 degrees elevation (I used the JPL Horizons Ephemeris, which anyone can use).
The orbit of the moon is inclined about 5 degrees from the ecliptic, but the Earth is tilted (obliquity) about 23 degrees. So the moon can be overhead as far north as about 28 degrees. So it will get pretty high in NE Oklahoma.
Order of Kilopi
Well ...
To be picky, the orbital plane of the Moon shifts quite rapidly in the sidereal frame. It stays tilted at around 5 degrees to the plane of the Earth's orbit around the Sun, but it twists in the ecliptic plane.
If it weren't for this "nodal precession", eclipses would occur on approximately the same dates, twice a year. Instead, they slide around the calendar as the "eclipse season" drifts with the Moon's orbital precession.
So, in summary: the Moon moves in a tilted ellipse around the Earth, moving alternately closer and farther away each month. The tilt stays constant relative to the Earth's orbit, but the plane of the ellipse twists around the Earth. Meanwhile, within the orbital plane, the ellipse turns slowly like the hour hand of a clock, so that the closest and farthest points move slowly around the Earth.
It's "constant", but only in terms of these various constant motions! (And superimposed on that there are various minor perturbations that mean the whole thing never really properly repeats itself.)
Grant Hutchison
PS: (Edit) Some figures.
One full (clockwise) twist of the Moon's orbital plane on Earth's orbital plane takes 18.61 tropical years: so eclipse seasons come at 173-day intervals instead of 183-day (half-yearly) intervals. One full (anti-clockwise) turn of the Moon's orbital ellipse within its orbital plane takes 8.85 years. In the unlikely event anyone's interested, the technical terms for these two movements are "regression of the nodes" and "rotation of the apsides".
Last edited by grant hutchison; 2005-Dec-19 at 12:07 AM.
Order of Kilopi
Indeed, I wonder if when you stop posting if your brain will explode from not releasing your scientific information.You're right Dragon Star! You have to move fast around here...
Anyone else think that grant hutchison also knows too much?
Order of Kilopi
Not picky, that's an important correction, 18.6 years is in fact pretty quick on human timescales. I should have said "in the lifetime of a salmon" or some such thing. It's hard to keep track of all the cycles within cycles, it only makes it more amazing that even ancient cultures were able to do it. The bottom line, twa47, that no statement about astronomy is 100% correct, including this one.
Order of Kilopi
My deeper fear is that once I've said everything I know, I'll have to stop posting! (Or is that not necessarily true...?) But this is the beauty of being wrong, there's always something more to get straight.Indeed, I wonder if when you stop posting if your brain will explode from not releasing your scientific information.
Order of Kilopi
Oh now common, there are always new n00bs to set in their place, plus I will always be around for correcting!
Order of Kilopi
I suppose you're right. And there's always more to learn-- should we tell twa47 that the Moon is very slowly getting farther from the Earth, and why, or doesn't he yet Need To Know?
Order of Kilopi
Hmm, let's let him decide on that, if he wants to know, he can tell us.
So how about it twa47? Is this something your interested in?
Newbie
Yes, you have overwelmed my pea brain. Thanks for the info. I could have sworn I saw the moon set in the south west a couple of weeks ago.
Newbie
That would have been setting just behind the sun.
Order of Kilopi
And you'd be right. That's why in my generalization I specified the behavior of the nighttime (full) winter moon. That dawn/dusk/daylight (new) Moon is different, and more similar to the behavior of the winter Sun instead of the summer Sun.
Another table, this time for the approximate new moon, December 1, roughly Oklahoma:
Near dawn, the moon rose about 124 degrees east of north, 34 degrees south of due east.Code:W 98 00, N36 00 Altitude and Azimuth of the Moon Dec 1, 2005 Central Standard Time Altitude Azimuth Fraction (E of N) Illuminated h m o o [Moonrise] 07:40 -0.6 123.1 0.00 07:50 1.4 124.5 0.00 [Moonset] 17:00 1.2 234.3 0.00 17:10 -0.8 235.7 0.00
Near dusk, the moon set about 235 degrees east of north, 35 degrees south of due west.
Order of Kilopi
Yes. See how it works? The Moon moves north and south of the equator every month, whereas the Sun does it once a year - they're both travelling around the sky in big circles that are tilted relative to the Earth's equator.
When the Moon's near the Sun (crescent Moon), it follows roughly the same path as the Sun: in summer, it rises in the NE and sets in the NW; in winter, it rises in the SE and sets in the SW. When the Moon's full, it follows the opposite rules from the Sun, as we've already discussed.
(So if you overwinter in the Antarctic, when the Sun is out of sight for months on end, you'll never see a crescent Moon, but the full Moon will be visible. It'll kind of spiral into view during half-phase, travel around the horizon for a week getting more and more full, then spiral down again for another week while it wanes to half phase and sets.)
Grant Hutchison
Order of Kilopi
And to connect Grant's Antartica test case to the other things that have been said about phases, note that in the Summer where the Sun is out all the time, the Moon would still follow the exact same behavior as Grant described, but the phases would be different. Since the Sun is up, you'll see the crescent phases but not the Full phase, so as the Moon does its upward/downward spiral day after day, it will go from half-phase (which technicallly is called quarter-phase, since it's 3/4 of the way around it's orbit) to a New Moon when it is as high as the Sun and sticks close to the Sun for a day or so, and then back to a half-phase (again, a quarter-phase is more correct since it's now 1/4 of the way from New to back to New again).
Just to clarify the terms a bit more, if you are confused about the quarter vs. half issue, it's not your fault. Phases go: New, First Quarter, Full, Third Quarter. This means Full = Second Quarter = Half way around, i.e., full=half and half=quarter. It's a bit 'loony'.
Established Member
Ba dump bump
Order of Kilopi
Well, the terminology is confused. "Half phase" is generally taken to mean the same as "first quarter" and "third quarter" (for an example showing this, see this page, under the "Aristarchus of Samos" section).
First quarter and third quarter are sometimes called "first quarter phase" or "third quarter phase", which has led to the collective term "quarter phase", which therefore means the same as "half phase". (Sigh.) It all depends on whether you think about the phases as involving the visible disc or the whole surface of the moon.
(I'm not sure, but it seems to me that "half phase" or "first/third quarter" are the more common usages for the phases of the inferior planets Mercury and Venus.)
With that in mind, I confess I intended to type "half moon" in my Antarctica post, since most people have a clear understanding of that; but I obviously messed up.
For absolute clarity, I think the only answer is to use the astronomical term "dichotomy": but not many people outside astonomy have encountered it.
Grant Hutchison
Established Member
Precession of the Moon's nodes over 1 saros cycle (~18 years). Click for animated GIF.
Order of Kilopi
Lovely.
You can also pick up the movement of the perigee as a sort of "sloshing" movement of the orbital ellipse at ~twice the rate the nodes are moving.
Grant Hutchison
Newbie
Grant, Thanks, my well educated friends that were telling me I must be wrong, have recieved an education from you and me. I want to thank you all for educating me.
A Vietnam Combat Vet watching the Universe.
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