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.
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.
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.
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.
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.
Bottom line: Tonight, use the waning gibbous moon to locate Regulus, the Royal Star!
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.