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Dekzper
2011-Jan-02, 08:23 AM
I discovered this site last night while I was googling for info on these questions: During the year, Earth orbits the sun with a (roughly) 23 degree equatorial tilt to the ecliptic. Our moon's orbit is inclined to Earth's equator by (roughly) 5 degrees. That means the moon's orbit is tilted (+/-) 23+5 degrees to the ecliptic.
1. Around the time of the winter (northern) solstice: When the moon is farthest from the sun, is it above or below the ecliptic?
2. Around the time of the summer (northern) solstice: Is the opposite true?

Thanks in advance for any help. It would be very appreciated. :)

Hungry4info
2011-Jan-02, 04:37 PM
1. Around the time of the winter (northern) solstice: When the moon is farthest from the sun, is it above or below the ecliptic? Above.

2. Around the time of the summer (northern) solstice: Is the opposite true? Yes.

chornedsnorkack
2011-Jan-02, 05:35 PM
Ecliptic has no upper or lower side.

Dekzper
2011-Jan-02, 07:34 PM
Ecliptic has no upper or lower side.

Sorry, my bad. What I meant by "above" was the side of the ecliptic containing the Earth's northern pole. I think Hungry understood that but I do need to be more clear with my questions.

Hungry, thanks. That helped me finish my Earth-Moon model. :)

ngc3314
2011-Jan-02, 07:53 PM
The direction of the ~5-degree tilt between the Earth's and Moon's orbits rotates with an 18.6-year period (the Saros cycle) driven by solar perturbations. The Moon's declination range goes from maximal +/- 28 to minimal +/-18 and back during this cycle.

Dekzper
2011-Jan-02, 10:34 PM
The direction of the ~5-degree tilt between the Earth's and Moon's orbits rotates with an 18.6-year period (the Saros cycle) driven by solar perturbations. The Moon's declination range goes from maximal +/- 28 to minimal +/-18 and back during this cycle.

Thanks for that. :) I'm studying that, apsidal precession, nodal precession, and lunar standstill now but it will proly take some time to get it into the model. :wall: I'll also need to find out what the current declination of the moon is. Does anyone know when the last Saros cycle officially started?

Centaur
2011-Jan-03, 08:10 PM
Our moon's orbit is inclined to Earth's equator by (roughly) 5 degrees.

I'll also need to find out what the current declination of the moon is. Does anyone know when the last Saros cycle officially started?


Actually, the “mean” 5.15° inclination of the lunar orbital plane is relative to the ecliptic (Earth’s orbital plane) and not to Earth’s equator. As ngc3314 noted, inclinations up to this approximate value can be added or subtracted from the Earth’s current axial tilt of 23.44° to obtain the Moon’s extreme declinations each month. Indeed, this amount goes through a precession cycle of 18.6 years; the declinations were most extreme in 2006 and will be minimal in 2015. Also keep in mind that due to a perspective effect, the Moon’s declination is not the same for an observer on the Earth’s surface as it is for the Earth’s center.

The Moon’s declination is constantly changing and goes through a full cycle every 27.3 days. As mentioned earlier, the amplitude of those declination swings goes through a larger cycle every 18.6 years. Below are the results of my calculations for the extreme geocentric declinations and celestial latitudes of the Moon during the remainder of this month.

2011 JAN 10 at 20:37 UT – Maximum Northern Latitude of 5.3°
2011 JAN 16 at 22:48 UT – Maximum Northern Declination of 24.2°
2011 JAN 24 at 03:50 UT – Maximum Southern Latitude of 5.2°
2011 JAN 29 at 16:25 UT – Maximum Southern Declination of 24.2°

There are 39 Solar Saros Cycles currently in effect. Of course there are also Lunar Saros Cycles. The partial solar eclipse of 2011 JAN 04 is in Solar Saros Series #151 and is the 14th of 72 members. It began on 1776 AUG 14 and will conclude on 3056 OCT 01. The most recently initiated Solar Saros Series was #155 which commenced on 1928 JUN 17 and will conclude on 3190 JUL 24. The next Solar Saros Series to be initiated will be #156 commencing on 2011 JUL 01 and concluding on 3237 JUL 14.

Centaur
2011-Jan-04, 04:42 AM
...I'm studying that, apsidal precession, nodal precession...

It might be noted that while the mean lunar nodes indeed precess through the ecliptic with a period of 18.6 years, the mean lunar apsides progress (not precess) through the ecliptic with a period of 8.85 years. That is too say that they rotate in opposite directions. This results in the mean ascending node and mean perigee passing through each other every 6.00 years.