Around mid-evening tonight – January 4, 2018 – look in the east for the bright waning gibbous moon. Although the star Regulus shines close to the January 4 moon, it might be hard to see in the moonlit glare.
What if you look and don’t see the moon? That’ll be because the moon has not risen yet. The exact rising times for the moon and Regulus depend on where you live worldwide. Click here for some recommended sky almanacs that’ll provide this information for your part of the world. Or use this custom sunrise-sunset calendar, and be sure to click the box for moonrise times.
Regulus is the brightest star in the constellation Leo the Lion. In skylore, it’s considered the Lion’s Heart. We draw in the stick figure of the constellation Leo on today’s sky chart, but you’re not likely to make it out very easily in the bright moonlight.
The moon and Regulus shine especially close together on the sky’s dome tonight as viewed in the Americas. In fact, the moon will actually occult (pass in front of) Regulus, as viewed from northern North America. From Anchorage, Alaska, for instance, the moon will occult Regulus on the evening of January 4, from 21:42 (9:42 p.m.) to 22:23 (10:23 p.m.) local time. The occultation times for over 900 localities can be found here but you must convert Universal Time to local time. Here’s how.
Regulus is located along the ecliptic, or annual path of the sun in our sky. The moon shifts from year to year with respect to the ecliptic, but currently it’s situated such that it’ll occult Regulus for several more months to come. The first of the series of monthly lunar occultations of Regulus started on December 18, 2016. The series will conclude on April 24, 2018. Once again, we must emphasize that you must be on the right spot on Earth to witness any one of these lunar occultations of Regulus.
The moon travels eastward in front of the constellations of the zodiac in a period of about 27 and one-third days. So that’s why the moon will next pair up with Regulus on February 1, 2018.
Whether or not you can see the occultation tonight, we can all see Regulus near the moon. After rising, the moon and Regulus will climb upward and westward throughout the night, until reaching their high point in the sky around 3 a.m. local time (on January 5). Afterwards, the moon and Regulus will start their descent westward, to lord over the western sky at dawn.
The moon and Regulus, just like the sun, cross the sky each day from east to west. That’s because the Earth rotates on its axis from west to east each day. Although the moon goes westward relative to our earthly terrain, it actually moves eastward relative to the stars. Therefore, you’ll see the moon farther east relative to Regulus tomorrow evening, on January 5.
Bottom line: Look for the moon and Regulus to climb above your eastern horizon around mid-evening on January 4, 2018. From some places, the moon will pass in front of Regulus.
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.