A Disappearing Star!

A spectacular and rare celestial occultation is scheduled to happen on the late night of March 20th for selected readers of this column.  It’s nothing less than the brief disappearance of the well-known first-magnitude star Regulus in Leo, the Lion—and with it, disruption of its well-known “sickle” asterism marking the head of the Lion!

In writing this column, an attempt is generally made to highlight events readily seen by most of its readers, both in this country and often throughout the world (see the coverage of April’s total eclipse of the Moon in next month’s installment which can be seen by more than half the planet).  This event will only be visible within a narrow 40-mile-wide path crossing metropolitan New York where it begins and then in the following minutes sweeps northward through upstate New York into Ontario, Canada.  Regulus will snap out of view for up to 14 seconds beginning around 2:06 a.m. EDT.  Those in its path will see Leo temporarily missing its primary star—a strange sight indeed!

So what’s going to cause this celestial disappearing act?  It’s a tiny and very faint asteroid in our solar system called Erigone.  As it crosses the line of sight from us to Regulus, it will occult or block the star’s incoming light beam.  The celestial alignment involved in this event is simply amazing!  The distance of the asteroid from us is measured in millions of miles, while Regulus lies 77 light-years from us—or well over 400 trillion miles away. (This reminds me of the caption to a painting that used to hang in the old Buhl Planetarium in Pittsburgh.  Showing the stars of the winter constellation Orion rising and half-hidden behind the bare branches of a tree, it read: “O glorious geometry!  That a twig should hide a star.”)

To locate Leo and Regulus, set the rotating star chart on your Scientific’s Star and Planet Locator  to 2 a.m. on March 20th.  Note the familiar Big Dipper riding high in the northwestern sky.  As is well-known, a line from its “pointers stars” at the end of the bowl points upward to Polaris, the North Star.  That same line extended downward instead in the sky points directly at our target, now well up in the west at this hour.  Look for its “sickle” asterism representing the head of the Lion.  It appears like a backwards question mark with Regulus marking the tip of the handle.

The best approach to watching the occultation is to use the unaided eye itself rather than binoculars due to the super-wide-angle view of the former as compared to the relatively limited one of all but the widest-angle glasses of the latter.  And this is definitely not a telescopic event if you want to get the full effect.  The key here is to see the entire head of Leo as it normally appears—and then watch its dramatic change in appearance as Regulus suddenly disappears right before your eyes!

—James Mullaney

Former assistant editor at Sky & Telescope magazine & author of nine books on stargazing.  His latest is Celebrating the Universe! available from HayHouse.com.