On Thursday evening, May 4, we’ll get our second chance to see the Moon pass directly in front of the bright star Regulus. From across Australia, the star will appear to blink out of view before emerging from behind the Moon about an hour later.
There was a Lunar Occultation of Regulus back in February. It occurred around midnight and the weather wasn’t very cooperative. Most people were clouded out although amateur astronomer Ian Musgrave persevered to produced some great images of the event.
This occultation will occur in the early evening and providing the weather behaves, it’ll be a great chance to get family and friends outside for a bit of stargazing.
The Moon will appear in the northern sky, and Perth will miss seeing Regulus disappear as it occurs while the Sun is low in the west.
The Moon is just past its First Quarter phase, which means from here on Earth we see it evenly split into light and dark. Looking up at the Moon, the leftmost side appears in lunar day, while the other is in lunar night.
Regulus will move behind the dark or unlit part of the Moon, so it may look like the star just randomly blinks out when it disappears from view.
The star will reappear from the bright side of the Moon, which will be a little trickier to spot as Regulus competes with the Moon’s bright glare.
Regulus’ disappearing act as seen from various Australian cities (created based on OCCULT v4.2.0)
The Moon’s path across the sky lines up with Regulus every nine years. And while the star and the Moon will continue to meet up in the sky until April next year, this is the last occultation that is visible from Australia.
As an aside, Regulus and the Moon will cross paths for northern Australia on September 18, but it occurs during late afternoon.
What I like about lunar occultations is the reminder that we live in a clockwork universe. They show us how the Moon is forever inching across the sky.
That motion coincides with the phases of the Moon. During New Moon, the Sun and Moon are together in the daytime sky.
But as the Moon cycles through its phases, slowly growing from new to full, the Moon parts company with the Sun. We are seeing this as we watch the Occultation.
In a week’s time, the Moon will have broken away from the Sun and will fill the night with light during its lovely Full Moon phase.
Authors: Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museum Victoria