Thursday, March 20, 2014

Citizen Science and the Occultation of Regulus by Erigone

Last night at about 2:12am EDT the asteroid Erigone blocked the light of the star Regulus for observers in parts of the northeast.  From the observer's point of view, Regulus would appear to wink out for a period of up to 14 seconds.  Such an event is called an occultation. 

On the face of it, seeing a star vanish briefly seems an unlikely thing to get up in the middle of the night for, but it is true Citizen Science.  With nothing more than a stopwatch* and an accurate clock, we could contribute to astronomer's knowledge of this asteroid's exact orbit, its size, and even whether or not it has a satellite--a "moon" of its own.   Enough observers in the right places would allow determination of the size of Erigone's shadow--which is the size of Erigone itself--while brief occultations outside of this belt of shadow would likely show the presence of a companion.  Even observers in New York City (which was in the path of the shadow) could contribute, since Regulus is bright enough to be seen even there.

And consider the idea itself.  Astronomers know the orbit of Erigone (a 45-mile-wide rock way out in the main asteroid belt between Mars and Jupiter) well enough to line it up with a hot, powerful young star so far away (at 79 light years) as to be a mere bright point of light, and locate the shadow they cast to a region of the earth stretching diagonally across New York State and bits of Connecticut and Pennsylvania in a time nailed down to a few minutes.  The first prediction of this occultation was made ten years ago.

This is "pocket billiards" of a very high order!

Leo, with Regulus the brighest star in the lower right.
(The disk-like star images are a telescope artifact--by eye, they're all bright but tiny points.)

Alas! --I missed it.  After reading up on the event, figuring out the stop watch function on my wrist watch, and setting my alarm, I looked outside to find solid overcast.  And by this morning it was raining.  Mind you, eastern Massachusetts is well outside the occultation zone of Erigone itself, but I cherished the idea of being part of the effort to see if she might possibly have a satellite.  Even if--as was very likely--I saw nothing at all but Regulus shining steadily out of the constellation Leo, that would be just as useful: it would tell astronomers one place where a satellite definitely wasn't.  Combined with the simultaneous observations of hundreds of others, it could have given astronomers a pretty clear idea of the Erigone "system."

*Even the stopwatch isn't strictly necessary: we are advised that simply counting aloud, "one-cigarette, two-cigarette,..." allows accuracy to about a quarter of a second.

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