Last Quarter, Regulus, and the direction ahead

There is a grouping – two bright objects plus a geometrical abstraction – to be seen in the night between Sunday and Monday, November 20/21: the Moon, the star Regulus, and the Earth’s direction of travel.

Sky scebe 2016 Novenber 21 in earlymorning

The Moon comes to its Last Quarter position at Nov. 21 8:33 by Universal Time, which is 3:33 AM in eastern North America, 2:33 in the Central time zone, 0:33 on the west coast.  Its center is 1.3° south of Regulus; more, as seen from our northern latitudes.  Between them is the ahead-point (properly called the Apex of the Earth’s Way).  When the Moon is at Last Quarter, it is crossing in front of us, leading Earth in the journey around the Sun.

Since this grouping is 90 degrees west of the Sun, it is best seen in the small hours of the morning.  By waiting minutes longer past the time of the picture, you can try to see the spark of Jupiter as it rises, near the east point on the horizon.

If you want to rise at a more tolerable hour, much closer to sunrise, such as around 6, the Moon-Regus-EDOT grouping will have heaved over to the right, high in the south; and Jupiter will have sloped up to around 30 degrees high in the southeast, with Spica below it.  But the grouping will have loosened, the Moon getting away nearly 2 degrees to the left.  And it will be 60 degrees above the horizon, making the picture rather inconveniently tall for me to show.

Down below the horizon, the Sun is about to move from the constellation Libra into Ophiuchus.  But on this same date. Nov. 21, it reaches the longitude of 240 degrees from the March equinox, which according to the ancient astrological system, uncorrected for precession, means that it passes from the sign Scorpio to that of Sagittarius.


4 thoughts on “Last Quarter, Regulus, and the direction ahead”

  1. Guy, your last paragraph made me wonder if there was some slightly underhanded reason why the IAU defined the constellation boundaries such that Ophiuchus would be a zodiacal constellation. If it was me, I would have made that entire area of southern Ophiuchus part of Scorpius. Did they do that just to throw off the astrologers? Scorpius does intervene between Libra and Ophiuchus, of course, but only with a surprisingly small slice of celestial real estate.

    1. Interesting idea, but the conspiracy would have to go back to 1875, when Benjamin Gould laid down the constellation boundaries. (At least, I assume the Ophiuchus boundary was part of his work, not that of Eugène Delporte who completed the work, presumably for far-south constellations, in 1930.) To keep that part of the ecliptic in Scorpius, you would have to take away from Ophiuchus about four stars, Zeta, Theta, Phi, and Omega. That would leave Ophiuchus with very short legs below the level where he is gripping Serpens in his two hands! And those letters, in Ophiuchus, must have been assigned by Bayer in 1603.

      1. Debunking my conspiracy theories? That’s no fun! One asterism in particular that belongs to Ophiuchus in this part of the sky is a personal favorite, namely the elongated diamond created by Theta, Omicron, 44, and Xi Ophiuchi. Planets regularly parade right through their midst, and Omicron is a beautiful, easy double star with orange and bluish components. I almost wish my birthday fell in the late November / December time frame so I could say my real “sign” was Ophiuchus!

  2. I saw this earlier this morning but did not realize the EDOT was was grouped right there with them. I should have known it would be close given the phase the moon was in! Thank you so much for this diagram, I love it.

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