Sky ArchiveTonight

Moon and Regulus on December 16

The moon is some days past full on December 16, 2019, and so it’s rising late at night. On this evening, you might catch the moon and star Regulus – brightest star in the constellation Leo the Lion – rising in the east from mid- to late evening. If not, you can always get up before daybreak on December 17 to view this waning gibbous moon and star Regulus high in the morning sky. You’ll recognize them easily. Look first for the moon. That nearby bright star will be Regulus.

Visit Heavens-Above to see the moon’s present position in front of the constellations of the zodiac

Want to know when the moon and Regulus rise into your sky? Then go to Sunrise Sunset Calendars for the moon’s rising time (remember to check the moonrise and moonset box). Or try Stellarium online. It can help you find the rising time for Regulus for your specific location on the globe.

EarthSky lunar calendars are cool! They make great gifts. Order now. Going fast!

Regulus represents the Heart of Leo the Lion. It’s the only 1st-magnitude star to sit almost squarely on the ecliptic – the sun’s apparent annual path in front of the constellations of the zodiac. Of course, the sun’s apparent motion in front of the background stars is really a reflection of Earth’s revolution around the sun.

Stars in black on white with ecliptic line slanting past Leo.
Chart of the constellation Leo via the IAU. The ecliptic depicts the annual pathway of the sun in front of the constellations of the zodiac. The sun passes in front of the constellation Leo each year from around August 10 to September 17, and has its yearly conjunction with the star Regulus on or near August 23.

Regulus is also considered the most important of the four Royal Stars of ancient Persia. Possibly, Regulus’ proximity with the ecliptic elevated this star’s status. These Royal Stars mark the four quadrants of the heavens. They are Regulus, Antares, Fomalhaut, and Aldebaran.

Four to five thousand years ago, the Royal Stars defined the approximate positions of equinoxes and solstices in the sky. Regulus reigned as the summer solstice star, Antares as the autumn equinox star, Fomalhaut as the winter solstice star, and Aldebaran as the spring equinox star. Regulus is often portrayed as the most significant Royal Star, possibly because it symbolized the height and glory of the summer solstice sun. Although the Royal Stars as seasonal signposts change over the long course of time, they still mark the four quadrants of the heavens.

Diagram of Big Dipper.
An imaginary line drawn between the pointer stars in the Big Dipper – the 2 outer stars in the Dipper’s bowl – points in one direction toward Polaris, the North Star, and in the opposite direction toward Leo.

The star Regulus coincided with the summer solstice point some 4,300 years ago. In our time, the sun has its annual conjunction with Regulus on or near August 23, or about two months after the summer solstice – or, alternatively, one month before the autumn equinox.

Regulus will mark the autumn equinox point some 2,100 years in the future.

Antique etching of yellow lion with black stars scattered across it.
The constellation Leo, with the star Regulus at its heart, as depicted on a set of constellation cards published in London in about 1825. Image via Wikimedia Commons.

Bottom line: Tonight, use the waning gibbous moon to locate Regulus, the Royal Star!

December 16, 2019
Sky Archive

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Bruce McClure

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