Late tonight, millions living around New York City may witness the best stellar disappearing act ever seen in North America.
Lucky sky-watchers with clear skies across parts of the Northeast will observe a bright star momentarily wink out early Thursday morning.
Beginning at 2:07 a.m. EDT, the 45-mile-wide (72-kilometer-wide) asteroid named 163 Erigone will slip in front of the bright star Regulus, located in the constellation Leo, the Lion, causing the star to become invisible for up to 14 seconds.
This celestial disappearing act should be visible along a very narrow, 45-mile-wide corridor that stretches from metropolitan New York City through parts of Long Island, New Jersey, Connecticut, and up toward the northwest through the towns of Utica and Oswego, in upper New York State, reaching into Canada near the city of Kingston, Ontario.
Astronomers say while asteroid occultations happen all the time, they nearly always are too faint to catch with the unaided eyes, needing binoculars or telescopes to observe.
But this cosmic blackout will be the brightest asteroid occultation in recorded history for North America.
Astronomically speaking, it’s amazing to think that this stellar eclipse is merely a matter of a coincidental lineup of two cosmic objects that are at very different distances.
“While the star Regulus lies some 79.3 light-years [46 trillion miles] away from Earth, Erigone is in our solar system, in the asteroid belt between Mars and Jupiter, and is comparatively much closer at only 4,400 million miles [7,081 million kilometers] away,” said Hanno Rein, an astronomer at the University of Toronto in Ontario, Canada.
“On March 20th, Regulus, Erigone, and Earth will be exactly in one line so that [part of] Earth is in the shadow [of the asteroid], just like during a solar eclipse where the moon is blocking the light from our own star.”
Asteroid occultations are a boon to planetary scientists, because they offer a chance to gauge the physical properties of asteroids that are revealed by the silhouette they cast.
“Most asteroids are so small and so far away [that] they can never be seen as anything more than a point of light, even through the Hubble Space Telescope. But because we can predict with great accuracy how fast an asteroid moves across the line of sight, by timing how long an occultation lasts we can straightforwardly calculate the width of the asteroid,” explained Mark Hammergren, an astronomer at the Adler Planetarium in Chicago, Illinois.
And professionals are calling on backyard stargazers to widely watch this occultation and contribute their observations to an online data clearinghouse run by the International Occultation Timing Association (IOTA). See its website for more information about the event and how to participate.
“While one single occultation observation will only give us one line across the asteroid’s width, by combining multiple observations from distributed locations, we can generate a full profile of the asteroid,” Hammergren says.
Regulus is ranked as the 19th brightest star in the entire sky, so if local skies are at least partly clear it should be easy to find overhead, hanging low in the southwestern sky. The blue-white stellar beacon is the lead star of the constellation Leo, marking the heart of the lion. It is the brightest starry object in this part of the sky in the overnight hours.
But if you don’t know your way around the sky, you can use the moon as a convenient guidepost. At around 2 a.m., look for the moon in the south. Regulus will be about 70 degrees to the right of the moon, equal to about three times the span between your pinky and your thumb stretched apart and held at arm’s length.
Asteroid Erigone itself is very faint. At magnitude 12.4, it is some 26,000 times fainter than Regulus and can be glimpsed only by large telescopes.
The shadow of the asteroid will be traveling at 11,400 miles (18,346 kilometers) per hour and will make the star wink out at 2:06 a.m. for the New York City region, 2:07 a.m. along the shadow’s path that runs through central upstate New York, and 2:08 a.m. in Canada.
But even folks not along the path, from South Carolina up to Nova Scotia and Manitoba, should also try observing beaconlike Regulus during the occultation time (2:00 to 2:12 a.m. EDT) and record if they see it momentarily disappear.
“If there are enough data points, astronomers may also reveal the presence of a moon around the asteroid,” adds Hammergren.
Otherwise, Erigone is an unremarkable chunk of rock and metal that will never get very close to Earth. However, what is so incredible about this occultation is that its path falls across a highly populated region, so potentially millions of people can watch this event.
Join me, along with National Geographic Explorers, an astronaut, and questions from you, for our National Geographic Google+ Hangout to Explore the Wonders of the Universe. Post your questions to social media using #LetsExplore, and join us Thursday, March 20 at 2:30 p.m. ET (6:30 p.m. UTC).