From mid-northern latitudes on January 18, 2014, the waning gibbous moon and the star Regulus rise fairly close to one another about three hours after sunset. From the Southern Hemisphere, the moon and Regulus rise even sooner after sundown. No matter where you live worldwide, look for the moon and Regulus to adorn your eastern sky before bedtime tonight. Binoculars will help you to appreciate this star in tonight’s drenching moonlight.
Regulus is the brightest star in the constellation Leo the Lion. It’s the only first-magnitude star to sit almost squarely on the ecliptic, or path of the sun, moon and planets in our sky. The ecliptic on sky charts marks the sun’s yearly path in front of the backdrop stars. See the sky chart below for more detail.
Of course, the sun’s apparent motion through the constellations of the Zodiac is an illusion. It’s really our planet Earth’s orbit around the sun that makes the sun appear to move in front of these stars.
Yearly, the sun and the star Regulus have their conjunction on or near August 23. On this date, the sun and Regulus come up together at sunrise and set in the west together at sunset. Six months before or after this date – in the latter part of February – Regulus shines opposite the sun and is out all night long.
Note that the sun’s conjunction with Regulus comes about one month before the September 23 equinox. By definition, the sun enters the sign – not the constellation – Libra on the September equinox. Also, by definition, the sun enters the sign Virgo one month before the September equinox, and the sign Leo two months before the September equinox.
Since the sun has its yearly conjunction with Regulus about one month before the September equinox, that means Regulus, the constellation Leo’s brightest star, must reside very close to the border of the signs Leo and Virgo. But, technically, where does Regulus lodge – in the sign Leo or sign Virgo?
The answer: Virgo. Two years ago, in 2012, Regulus passed out of the sign Leo and into the sign Virgo. Slowly but surely, Regulus (and all the zodiacal stars) move eastward relative to the signs of the Zodiac. Somewhat more than two thousand years into the future, Regulus will enter the sign Libra, to mark the September equinox point.