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chornedsnorkack
2009-Jun-21, 06:09 PM
Were the Sun viewed exactly each 24 hours, it would trace analemma in sky. A projection of analemma is equation of time.

What figure would the Moon follow if it were viewed each 24 hours 50 minutes?

Gandalf223
2009-Jun-21, 07:23 PM
Dunno, but it should be pretty easy to visualize in Stellarium.

Now I just have to wait for someone who's not as lazy as me.

astromark
2009-Jun-21, 07:26 PM
You can not use the same set of rules for the moons track across the sky. The hands span to the east of where it was last night works for me... Its not the final word on its actual path., or location. Analemma is used to describe the Solar path. The Sun is at the northern tip today of its lazy 8. I would think that the lunar path is well documented to know how north south the lunar track is. Try the search for, in wickie...

grant hutchison
2009-Jun-21, 07:44 PM
It looks superficially similar (http://apod.nasa.gov/apod/ap050713.html) to the solar analemma.
However, it evolves from month to month as the nodes and apsides of the lunar orbit precess. So there's a north-south oscillation with a period of 18.6 years, moving with the nodes; and a change in shape with a period of 8.85 years as the apsides move. The shape change moves the centre of the figure-of-eight up and down the figure, adjusting the relative sizes of the top and bottom loops. I can't at present recall if, at the extremes, the figure-of-eight ever opens out into a simple loop, like the solar analemma seen from Mars (http://antwrp.gsfc.nasa.gov/apod/ap061230.html).

Grant Hutchison

Centaur
2009-Jun-21, 10:59 PM
Thatís a good answer from Grant. The question motivated me to modify one of my homemade programs to produce the desired images. Here are the results for my location over the coming month from June 22 to July 20. July 6 appears skipped because lunar transit occurs late on July 5 and then early on July 7. Indeed, the pattern would appear somewhat different each month, but it is something like a solar analemma.


http://www.curtrenz.com/Moonalemma.JPG

grant hutchison
2009-Jun-21, 11:21 PM
Thanks, Centaur. Your charts, taken with the APOD image for June 2005, shows the shifting cross-over in the figure-of-eight nicely. It's placed near the southern end of the figure in your chart, giving a large northern loop; whereas in the picture taken four years ago (about half an apsidal cycle) the cross-over was at the north end, giving a large southern loop. :)
The solar analemma as seen from Earth has a similar cycle, but spanning the 22,000-year period in which the Earth's perihelion moves around the calendar.

Grant Hutchison

Centaur
2009-Jun-21, 11:35 PM
Thanks, Centaur. Your charts, taken with the APOD image for June 2005, shows the shifting cross-over in the figure-of-eight nicely. It's placed near the southern end of the figure in your chart, giving a large northern loop; whereas in the picture taken four years ago (about half an apsidal cycle) the cross-over was at the north end, giving a large southern loop. :)
The solar analemma as seen from Earth has a similar cycle, but spanning the 22,000-year period in which the Earth's perihelion moves around the calendar.


Youíre welcome, Grant. Hereís another version for the period from 2015 JUN 16 to JUL 12 thatís a little closer to being symmetrical. I left out the dates because it made the image even more cluttered than in the first one. The first date is on top at the meridian and the following date is to its left.


http://www.curtrenz.com/Moonalemma2.JPG

mugaliens
2009-Jun-22, 03:48 AM
Were the Sun viewed exactly each 24 hours, it would trace analemma in sky. A projection of analemma is equation of time.

What figure would the Moon follow if it were viewed each 24 hours 50 minutes?

As the Moon is inclined 5.145 deg to the ecliptic, it varies between 18.29 deg and 28.58 deg to Earth's equator. Thus, in one month (27 d 7 h 43.1 min), it would trace a very squat analemma, but would not end where it began the month prior.

Over a year's period of time, however, it would trace 12.37 tiny analemas in a larger analema pattern.

Much like a spirograph... :lol: