The Moon, Libra, and "gateway" stars

Event Date: March 3rd

Time: 4:54(.44) AM

Brief

   The waning, gibbous Moon is nearing 3rd quarter, and about its highest in the sky not long before Sunrise.  At a little less than 2/3rds illuminated, it rose during the late evening yesterday, several degrees south of the Sun at this time of year for its current phase.  It is in the dim constellation of Libra the [weighing] Scales, and its glare makes even the brightest two stars of Libra hard to see.  I will label them anyway in the image below, as a reminder of their acting as "gateway" stars.  More about that reminder is in the detailed section, following this image.  As I have recently, I will this time show the classical illustration of Libra dimly overlapping its stick figure.  Most of the stars for the figure are too faint to see even without the Moon in the way.

Detailed

   

   The two stars that I mentioned, Zubeneschameli and Zubenelgenubi, used to mark the claws of Scorpious, with its distinguishable star pattern to Libra's southeast (bottom left).  As shown by the illustration, Zubenelgenubi does not mark the other scale, yet the top of the balance hanger...or whatever it's called!  That aside, notice that it is almost on the ecliptic, slightly north of it by a fraction of a degree.  The Moon's orbit took it south of this star less than 24 hours ago.  As the precession of the nodes for the Moon's orbit continues, it will finally start passing between the stars a little over a year from now, emphasizing the gateway term for the scale's stars.

   Even when the Moon's orbit has it south of the gateway, the outer planets--Mars through Neptune--have their orbits pass through the gateway at that celestial longitude.  Unlike the Moon, there is no precession of the nodes for Jupiter through Neptune over the course of thousands of years, while Mars' precession is much slower than that of the Moon.

This next image shows a zoom-in of the stars and the planets' orbits.  Uranus' orbit--in grey--just barely passes north of Zubenelgenubi.

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

   Now, as I keep using that term, you may wonder why else they are called gateway stars.  Although I am not certain, I can say that after passing them and Libra, the Moon, star and planets head towards the galactic center-area of the sky, where they pass near many deep sky wonders; I labeled some of those in this entry. As they get higher in the sky during evening viewing next season, I will start to show them magnified.