Late tonight, one of the Northern Hemisphere's brightest stars will be blocked by a massive asteroid, and if you live in the Northeast part of North America, you could be lucky enough to witness it.
At around 2:06 a.m. EDT, the 45-mile long asteroid Erigone will block out Regulus, the brightest star in the constellation Leo, for between 14 seconds and two minutes, depending on where you are. The occultation, as the phenomenon is called, will only be visible to viewers in New York City and parts of upstate New York, Long Island, New Jersey, Connecticut, and (wild card!) Ontario. According to a blog post published on the International Occultation Timing Association (IOTA) website, the event is a rare one:
Since Regulus is about 4 million times farther away from us than the asteroid, you can imagine that many factors need to be properly aligned for this event to be visible from our planet. First the asteroid must pass in front of the star. Then the shadow of the asteroid must fall on Earth in an area where it is night, and of course the sky must be clear (frequently not the case in March in the Northeast part of the USA). Next the orbit of the asteroid and the location of the star must be known with sufficient accuracy for the prediction of where on Earth the shadow will pass to be made with some reasonable amount of certainty.
Sky & Telescope editors called the event the "best and brightest 'asteroid occultation' ever predicted for North America." They add that because Regulus is so bright, you don't need any tools or expertise to spot the occultation, even in a city with as much light pollution as Manhattan.
Here's what you need to know ahead of the occultation tonight:
How to watch
If you're in one of the aforementioned locations and are interested in the event but not interested in finding a telescope, you can figure out where constellation Leo is yourself, according to the editors of Sky & Telescope:
If the sky is clear, Regulus will be a cinch for anyone to spot — no astronomy experience required! Around 2 a.m. or a bit before, go out and face the Moon. Extend your arms straight out to your sides. Regulus will be straight above your right hand, roughly as high as the Moon is. It's the brightest star in that area.
Plus, there are a bunch of constellation maps that should theoretically help you figure out where the star is.
If you don't live in one of the aforementioned locations, you can still catch a live broadcast of the event, scheduled to start at 1:45 a.m. EDT.
Where to watch
Anyone along this map should be able to see the occultation (unless the sky is too cloudy, which is likely in New York City).
According to the New York Post, astronomers will be at four bars in Manhattan and Brooklyn to "encourage people to look, and tell them how to do it." So if you're in the neighborhood, you can stop by Art Bar, Ding Dong Lounge, the Way Station or Pacific Standard to chat with some knowledgeable, if buzzed, astronomers.
Otherwise, any spot with a clear view of the sky should work.
When to watch
According to IOTA, viewers should expect to see the occultation within a four minute window that correlates to your location:
2:04-2:08 : NYC, Long Island, CT, NJ, Westchester
2:05-2:09: Hudson Valley, Putnam and Duchess counties to Albany and Binghamton
2:06-2:10: Watertown and Ontario
More details can be found here.
How to report what you see
Scientists hope that viewers will note when they saw Regulus disappear and for how long, so that they can get a better sense of the type of asteroid Erigone is. It should be pretty easy for those with Apple devices: you can download an app that lets you time the occultation and submit the information to IOTA from your iPhone or iPad. Others can refer to the Regulus occultation public reporting page, which gives step-by-step instructions on how to report your observations.