On the evening of October 14, 2017, you won’t see the moon. That’s because the moon will be a waning crescent visible from across Earth only in the wee morning hours. No matter where you are, if you’re up early on the mornings of October 14-16, you’ll see the waning crescent moon near Regulus, the brightest star in the constellation Leo the Lion. Or … you won’t see Regulus. That’s because, on October 15, the moon will occult this bright star, or hide it from view.
Notice on our chart at the top of this post … we’re not showing a moon for October 15. That’s because, if we did, it’d hide the star Regulus from view. The occultation of Regulus on Sunday morning, October 15, will be visible from much of the United States (except for the Pacific West Coast), Mexico, the Caribbean or southeast Canada.
Look at the worldwide map below via the International Occultation Timing Association (IOTA). Every spot in between the solid white lines sees the occultation in a nighttime (predawn) sky, whereas the short blue lines indicate where the occultation happens at dawn and the red dotted lines where the occultation occurs in daytime.
The star will disappear behind the moon’s illuminated side and then reappear on its dark side. For your convenience, we list the local occultation times for various localities in the United States.
Lunar occultation of Regulus on October 15, 2017
New York City, NY
Occultation begins: 5:44:03 a.m.
Occultation ends: 6:43:25 a.m.
St. Louis, MO
Occultation begins: 4:29:48 a.m.
Occultation ends: 5:26:30 a.m.
Occultation begins: 3:31:04 a.m.
Occultation ends: 4:15:44 a.m.
Eastern Daylight Time = UTC – 4 hours
Central Daylight Time = UTC – 5 hours
Mountain Daylight Time = UTC – 6 hours
Regulus is known as the heart of the Lion in Leo. It’s the only first-magnitude star – that is, the only bright star among all the sky’s brightest stars – to sit almost exactly on the ecliptic or sun’s yearly path in front of the constellations of the zodiac.
The moon in its monthly journey around Earth moves more or less along the ecliptic, too. It can swing anywhere from 5o north to 5o south of the star Regulus. In cycles of about 9 years, however, the moon actually occults – passes directly in front of – Regulus once a month for a period of about one and one-half years. For instance, the last occultation series began on January 7, 2007, and ended on May 12, 2008, staging a total of 19 occultations.
The present occulation series began on December 18, 2016, and will end on April 24, 2018. Once again, there will be a total of 19 occultations in the series. But to see any lunar occultation of Regulus, you have to be on the right spot on Earth.
For the fun of it, we list the dates for this occultation series:
1. December 18, 2016
2. January 15, 2017
3. February 11, 2017
4. March 10, 2017
5. April 12, 2017
6. May 4, 2017
7. May 31, 2017
8. June 28, 2017
9. July 25, 2017
10. August 21, 2017
11. September 18, 2017
12. October 15, 2017
13. November 11, 2017
14. December 8, 2017
15. January 5, 2018
16. February 1, 2018
17. March 1, 2018
18. March 28, 2018
19. April 24, 2018
Exactly midway through the occultation series – on August 21, 2017 – the moon actually occulted Regulus on the same date that the moon totally eclipsed the sun.
How’s that for a great coincidence?
Bottom line: On the morning of October 15, 2017, watch for the moon to shine in the vicinity of Regulus, or to occult Regulus. The moon will appear in front of the constellation Leo for the next few days.
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.