Tonight – February 1, 2018 – the full-looking waning gibbous moon moon closely partners with Regulus, brightest star in the constellation Leo the Lion. Look for them in the east at nightfall or early evening. They climb highest up for the night at roughly 1 a.m. local time and sit low in the west as darkness gives way to dawn on February 2.
The moon most recently turned full on January 31 at 13:27 Universal Time. It won’t turn full again until March 2 at 0:51 Universal Time. That means no full moon in February 2018 at all, but two full moons in January 2018 and March 2018. The second of two full moons to occur in a single calendar month is popularly called a Blue Moon.
From North America, we see the waning gibbous moon to the east (below) Regulus. However, as seen from Europe and Asia, the moon appears higher up relative to Regulus. In fact, if you’re at just the right spot on Earth, the moon will actually occult (cover over) Regulus for a portion of the night tonight.
The February 1, 2018, occultation of Regulus appears in the night sky in northern Asia and northern Europe.
This occultation is part of a series of monthly lunar occultations of Regulus that started on December 18, 2016. The series will continue until its conclusion on April 24, 2018.
The moon and Regulus go westward during the night for the same reason that the sun travels westward across the sky during the day. The Earth spins from west-to-east on its rotational axis, making it appear as if the sun, moon, planets and stars move westward across the sky while the Earth stays still.
In fact, of course, it’s the Earth that’s spinning, causing that westward shift, and, meanwhile, the moon’s orbital direction is always eastward, or toward the sunrise direction, in our sky.
Note the moon’s position relative to Regulus tonight. Then note its position relative to Regulus tomorrow night – or 24 hours later. The moon’s change of position in front of the background stars lets you know how far the moon revolves around our planet Earth in one day.
Regulus is well known for its extremely fast rate of spin. Our sun takes nearly four weeks to complete one spin on its axis. In contrast, Regulus spins full circle once every 16 hours. This star has an equatorial diameter that’s 4.3 times greater than the sun’s but it still rotates at 700,000 miles (1,100,000 km) per hour.
At that speed, you could reach the moon in a little over 20 minutes!
Bottom line: Enjoy the pairing of the waning gibbous moon and Regulus – brightest star in Leo the Lion – on February 1, 2018! From some places the moon will pass in front of (occult) 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.