The moon is on Monday going through a remarkable celestial event—the only one of its kind in a 28-year window.

In under 24 hours, the moon will pass in front of three planets and one of the sky’s brightest stars. The last time it obscured three planets in so short a period was in 2008, and the next will be in 2036.

Astronomers refer to the moment when one celestial body blocks out another in Earth’s sky as an “occultation.” It happens fairly regularly as the moon orbits our world, but it’s unusual for so many bodies to be involved in this way.

Late Sunday and Early Monday Eastern Time, the moon passed in front of the planet Venus, and the star Regulus.

Regulus is a well-known star, known for its place among the 22 “first magnitude stars,” so called because they are the brightest in the night sky. Only four of these can be occulted by the moon, the other three being Aldebaran, Spica and Antares.

On Monday evening, the moon will move in front of Mars, at 4pm EST, and Mercury, at 7pm EST.

Skygazers in North America will see the three planets and the star arranged in a wonky diagonal line, with the moon passing downward through them. Even though it happens partly during daylight hours, if you have access to a telescope and can see the moon, just observe it as it moves through the sky.

2017 sept 17 18 moon venus regulus mars mercury

Unfortunately for Americans, however, the event will be best visible in Australia, New Zealand and Indonesia.

If you want to know when the next occultation is happening—even less rare small-scale events can be fascinating to observe—you can head over to the International Occultation Timing Association (IOTA) website.

As well as looking cool, occultations have some scientific usefulness too. According to IOTA, data gathered during occultations has helped astronomers to refine their understanding of the exact positioning of celestial bodies.

Bonus: watch this spectacular footage of Saturn as it emerges from behind the Moon during an occultation on 22 May 2007. Wow.

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