March 20: Regulus Occulted

Thursday, March 20, brings two celestial events: the spring equinox and the occultation of Regulus.

Anyone who is bitten with the travel bug and does not list sleep as a priority above stargazing can drive a relatively short distance to witness a pretty cool, but fleeting, event. Shortly after 2:05 a.m., Regulus, a bright star in Leo, will be occulted by asteroid Erigone for 14 seconds.

Should a clear sky grace us, anyone in the nearly 70-mile-wide path in which the occultation will be visible (this path unfortunately does not include New London County) will see Regulus disappear for 14 seconds as the 45-mile-wide asteroid passes in front of it.

The shadow of the asteroid will be slightly larger than the asteroid, oval shaped and about 67 miles wide. The difference in size is an effect of the shadow being projected onto the earth at an angle. The asteroid's shadow will be traveling from southeast to northwest across the surface of the earth at more than 10,000 mph, or about 3 miles per second.

However, the asteroid's size gives us about a 14-second maximum occultation near the middle of the asteroid, shorter nearer the edges. The shadow will first touch land in Bermuda at about 2:02 a.m. our time (which will be 3:02 a.m. in Bermuda since they are on Atlantic Daylight Time, one hour ahead of us). It will then race northwest across the Atlantic Ocean. About four minutes later, around 2:06 a.m., the shadow will pass over Long Island (both Nassau and Suffolk counties), New York City (all boroughs), and western Fairfield and Litchfield counties in the homeland.

The asteroid's shadow is a bit larger than the asteroid because it hits Earth at an angle. It will move on a southeast-to-northwest path that will extend from New York City to Oswego in New York state and continue northwest into Ontario, Canada.

In the small hours of Thursday morning, at any time from 1:30 a.m. until the occultation, an easy way to find Regulus is to face the moon and stretch your arms out horizontally to each side. Now turn your head to the right and sight along your right arm; Regulus will be directly above your right hand, about the same distance above the horizon as the moon. Both will be about halfway from the horizon to directly overhead. Regulus will be the brightest star in that part of the sky.

The word "Regulus" is Latin for "prince" or "little king." As far as stars go, Regulus is kind of an oddball. It is actually a multiple star system consisting of four stars. The light output comes mainly from Regulus A. Regulus B, if seen in isolation, would be a binocular object of magnitude 8.1, and its companion, Regulus C, the faintest of the three stars that has been directly observed, would require a substantial telescope to be seen, at magnitude 13.5.

So where does the fourth star come in? Regulus A is actually a binary star: the secondary star, which orbits A, has not yet been directly observed because its light has been drowned out by A. You can see the B and C pair through an amateur telescope, though, as they lie far enough away from Regulus A.


March 16: Full moon.

March 20: March Equinox. The sun will shine directly on the equator and there will be nearly equal amounts of day and night throughout the world. This is also the first day of spring in the Northern Hemisphere and the first day of fall in the Southern Hemisphere.

March 30: New moon. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.


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