Moon near celestial equator: Mintaka comparison

Event Date: January 30th

Time: 12:43(.43) AM

Brief

   As we turn the calendar into a new day, a little more than six hours from my last entry, I will turn attention the the waning, gibbous Moon, which starts its time in the eastern sky, north of the celestial equator.  Later into the night, it crosses descending node and is seen a bit south of the equator.  

Now, you may be asking yourself, why does he bring this up??

Last week in this entry, I emphasized that the star Mintaka was the closest to the celestial equator, among stars easy to see with the eye.  I also mentioned that as a result, the star nearly traces out the celestial equator as we watch it rise almost directly east, and see it set directly west.  Seen below is the Moon rising, its orbit, celestial equator and ecliptic.  I am showing it when it crosses the equator, hence the seemingly random time listed.

click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.

Detailed

  When Mintaka was at opposition during the last few days of September, we would beable to see it rise during deep civil twilight, and set before dawn.  Although planets don't have the same type of oppositions as the outer planets, with some being far from the ecliptic, having the Sun at elongations near 180º from them once a year, gives us that chance to watch them move through the sky, and trace out their latitude.  Anyone staying up viewing all night do long-exposure astrophotography of Mintaka could make an image of the star's path.  Relating this to the Moon and getting back to that, our satellite is only about 8 arc-minutes north of the equator at the time above, and crosses it at 12:43 AM.  About an hour and a half later, the Moon is almost exactly the same declination as Mintaka.
   What is even more interesting about the Moon, is that because of precession of the nodes, it crosses the celestial equator at a different longitude each time.  Therefore, different stars have close encounters, or occulted by the Moon for months at a time for some years, and then for other years, the Moon may miss some of the same stars it occulted by over 10º.  Watch the Moon closely in a telescope on some evenings when there is less change in the Moon's (dec)lination, and find that at times, the precession of the nodes keeps it a particular dec for several minutes, of even a few hours.  The benefit of this of course, is that the telescope's dec adjustment--if manual--doesn't have to be change.  In the case of now however, when the Moon is quickly changing declination as shown by the ecliptic, a manual telescope will require regular "tweeking" of the the dec control.  If you have a small, equatorial telescope, particularly one that tracks via an electric motor/gears, you will have the most experience with this, instead of someone else viewing with an alt/az telescope.