Moon and Regulus tonight

In the night between February 28 and March 1, the nearly Full Moon gets in front of Regulus, as seen from the north of North America and from the Atlantic part of Europe.

Regulus is the 21st brightest star, but its prestige seems higher, because of its kingly name, because it is the heart of the celestial Lion, and because it lies close beside the ecliptic, like a signpost to the travels of the Sun, planets, and Moon.

The Moon is in conjunction with Regulus 14 times this year – because twice in March and twice in November.  The first five times, the Moon in its continually varying path passes close enough on the star’s north that it occults it – hides it – as seen from Earth’s northern end.

The third of these conjunctions, on March 1, happens at about 6 hours Universal Time.  So that is the middle time of the occultation.  It is 6 AM for Britain, but for North America it is 1 AM in the Eastern time zone, midnight in the Central, and back in February 28 for the more westerly zones.  (There, it is February rather than March that has two Moon-Regulus conjunctions.)

Depending how deep north you are into the occultation zone, the event is a mere blink (a “grazing” occultation), or a span of up to two hours between the moment when the star disappears into the Moon;s advancing edge, and the less easily anticipated moment when it pops out of the other edge.

And both edges are, this time, dazzlingly bright.  For it happens only 19 hours before the Moon becomes Full (March 2, 1 UT).

Our sky scene, for the Central time zone, is at an hour after the Sun has set in the west, and about two hours after the Moon has risen in the east.  You can see that the Moon will pass Regulus about midnight.

And that a day’s journey ahead of the Moon is the “anti-Sun” (which we can also call Earth’s shadow),  past which the Moon will go at the Full moment.

In this diagram of the occultation,

blue circles at hourly intervals are the areas on Earth from which the occultation is seen – we could call them the shadow of Regulus’s light cast by the Moon.  The flanking ones are only approximate, because of Earth’s rotation.

The sub-diagram to the right shows (facing in the opposite direction) the star appearing to pass below the virtually Full Moon – as seen from the center of the Earth.  For a more northerly latitude, such as the contiguous U.S., the star will be closer to the Moon, and from northern Canada it will go behind the Moon.

There is a more exact map of the occultation’s limits in the website of IOTA, the International Occultation Timing Association:

http://asa.usno.navy.mil/cgi-bin/occnwdo.cgi?dir=2018/occns&file=occn.2018Mar01.Regulus&body=Regulus

The graze limit passes over Alaska, a great deal of Canada, Maine, the Azores, and northwest Africa.

I haven’t yet added a section on occultations to “Astronomical Calendar 2018” (reachable by clicking the tab at top), but have added one on meteor showers.  It owes much to help from Alastair McBeath, but has been delayed by more of a struggle than I expected or could tersely explain, except by saying that meteors are a subtle subject.

“My space invention” (I’m told that that is a trending tweet and I should bow to it) would be a Regulator of meteor streams.  It would attach either to each comet, constraining it to shed its debris in a narrower line; or to the I.M.O.  (International Meteor Organization), constraining it to unanimity on its terminology and predictions.