Gloomy weather over New York could drown out a rare opportunity to see a bright star disappear from the sky very early tomorrow morning during what’s known as an “occultation.” The star Regulus, one of the brightest points in the constellation Leo, should appear to “wink out” for about 14 seconds when the asteroid (163) Erigone passes in front of it Thursday just after 2:05 a.m. EDT.
Clouds and rain could spoil the sight. “They’re forecasting about 90 percent cloud-cover, with a 65 percent chance of rain,” says astronomer Bob Berman, who will co-host a live Webcast of the event hosted by the Slooh Space Camera. “That’s pretty dismal.” In fact, the weather is so bad that Steve Preston, an observer with the International Occultation Timing Association (IOTA), which has been anticipating this event for about 10 years, is sitting the night out. “I was going to fly to Albany, but I changed my mind yesterday and bailed on my plans. I hope I made the wrong decision,” he says, adding that a break in the clouds could give some viewers a chance to see the occultation.
The alignment would be visible along a large wide swath extending from Long Island and New York City up north and west into Canada. Given clear skies, observers would see Regulus disappear as the 45-mile-wide asteroid Erigone, which is too dim to spot on its own, passed in front of it. Such asteroid-bright star alignments, especially over populated areas, are few and far between. “I’ve been a professional astronomer for over 40 years and I have never seen an occultation of a star this bright,” Berman says. “That’s how rare it is.”
Astronomers are still hoping that the cloud-cover will break up somewhere along the occultation’s path—a small chance of clear spots near the Catskills and New York City is predicted. If a break occurs, observers stationed all along the path of sight should catch it. Slooh’s astronomers, for example, will send direct video feeds from across the region, so viewers of the live Webcast can see it. “If this breaks anywhere, we’ll get it,” Berman says. The Webcast will also include telescope views of the asteroid from outside the occultation’s path, and commentary from astronomers and members of IOTA. The broadcast is set to start at 1:45 am EDT, and is viewable at http://www.slooh.com, or at the bottom of this page.
Intrepid stargazers who want to give it a shot from their own backyards can find Regulus by following the two pointer stars at the end of the Big Dipper opposite the direction of the North Star. This line will take you right to the constellation Leo, the Lion. In that group, the brightest star is Regulus.
IOTA members chase occultations not just for the show, but for the chance to learn something new about asteroids and the stars they block. With enough observers gathering precise timing information about when an occultation is visible from their location, the group can map out a two-dimensional picture of the shape of the asteroid. The technique is illustrated in a graphic made during the 2011 occultation by the asteroid (90) Antiope here: http://occultations.org/.
“Quite often occultations are really the only way to get a fairly accurate snapshot of the asteroid,” Preston says. “In the case of Regulus, there was one other tidbit of information we were hoping to learn.” Some observations of Regulus suggest the object is not just one star, but two—that in fact a hidden white dwarf star orbits Regulus in a close binary system. If Regulus is a double star, it should be evident during the occultation, because the asteroid should pass over each star at a slightly different moment. “We were hoping we’d have the chance to detect the companion star in the light curve,” Preston says. While that possibility is not eliminated, the unpromising weather makes such a detection unlikely.
If tonight’s occultation is a no show, stargazers will have to be patient. The next major chance to see such a sight will come in 2023, when the bright star Betelgeuse in the constellation Orion will be occulted over southern Europe and Turkey. Mark your calendar!