The sightof a relatively bright star suddenly vanishing as a faint asteroid crosses infront of it, and then just as suddenly reappearing several seconds later is anexceedingly rare and startling celestial occurrence. But it's happening in thepredawn hours on Tuesday and lucky skywatchers across parts of Canada and thewestern United States may have a chance to see it.
Astronomersrefer to such an event as an "occultation" — a temporary hiding ofone celestial object by another such as a planet moving in front of a star asseen from Earth. In this particular case, however, the occulting body will be aminor planet: a tinyasteroid known as 824 Anastasia. ?
Thestar in question is Zeta Ophiuchi, the third brightest star in the constellation ofOphiuchus, the Serpent Holder. At magnitude +2.6,it's a star that's bright enough to easily see with the naked eye; you don'teven need binoculars, although they would give a better view. ?
Theprojected path of this stellar eclipse — just 25 miles wide — will run fromSouthern California (encompassing a part of the Los Angeles metro area) thengoes north-northeast through central Nevada, west-central Idaho, northwestMontana and on up into Alberta, Canada, passing almost directly over thisprovince's two largest cities, Calgary and Edmonton.
"Anyonewho can see and count, lives in or near the eclipse path, and is willing to getup in the middle of the night and go outside for about ten minutes, can help usmeasure the size and shape of this asteroid," said IOTA member BradTimerson. "We want as many as possible to try to observe the eclipse sincethe detail of Anastasia's shape that we can derive is proportional to thenumber of places from which the eclipse is observed."
Today,thanks primarily to the European Space Agency's star-trackingspacecraft Hipparcos, predictions of such eventshave greatly improved.
Ifyou are novice to astronomy and think you'll have trouble in locating ZetaOphiuchi, here is a reliable way of identifying it. You can try it during theearly evening hours of Monday, April 5, which will be many hours before theoccultation. ?
First,locate the familiar seven stars that make up the Big Dipper (around 11 o'clock,local time, the Dipper will be high in the northern sky, almost directlyoverhead).
That'syour target star: Zeta Ophiuchi.
Hereis a view of the shadow track of 824 Anastasia as it moves on asouth-to-north path across western North America. The solid parallel linesdefine the "best" estimate of the path, estimated to be 25 mileswide. But there is still some uncertainty which is why an additional set ofdotted lines are placed on either side of the path, suggesting that the starconceivably might appear to briefly wink out just outside of the main eclipseviewing zone.
"Evenan observer on the predicted central line has only a 26% chance to have anoccultation," Timerson said.
Here'swhat to do: With the tape recorder continuously running and WWV on the radio inthe background, call out "D" when the star disappears and"R" when it reappears (or, thinking it like a light, "off"and "on"). ?
"Ifyou had no eclipse of the star, just let us know that fact and send yourlocation in an e-mail message to reports@asteroidoccultation.com," wrote IOTA President David Dunham. "We preferthat you use a GPS receiver or Google Earth, to determine your longitude,latitude, and elevation above sea level."
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Joe Rao serves as aninstructor and guest lecturer at New York's Hayden Planetarium. He writes aboutastronomy for The New York Times and other publications, and he is also anon-camera meteorologist for News 12 Westchester, New York.
