The Brightest Star in the Night Sky Will Go Dark

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Sirius is one of the brightest stars in the sky, and it will go dark for a brief moment. Akira Fujii/NASA/ESA/Wikimedia Commons

It's hard to miss Sirius, the dog star. It's the brightest star in the night sky, after all.

But on Monday, Feb. 18, the star will go dark for almost two seconds.

It's the first time in recorded history that the star will dim, and it's all thanks to a 3-mile-wide asteroid.

Making Sirius blink

Sirius, located in the constellation Canis major, is easy to spot not just because of its brightness but because the three stars that make up Orion's Belt point down at it in the winter sky, at least if you live in the Northern Hemisphere. Follow the stars of the belt down to the southeast horizon and, boom, Sirius.

The star was first formally reported back in 1844 by German astronomer Friedrich Wilhelm Bessel. Eighteen years later, American astronomer Alvan Clark, spotted Sirius' companion star, Sirius-B. While nowhere near as bright as Sirius-A, Sirius-B has the distinction of being the first white dwarf star ever discovered.

At only 8.6 light-years away, Sirius is also one of the closest stars to Earth. Its proximity and brightness have made it a fixture in societies across history. For the ancient Egyptians, Sirius' rise in the late summer sky was the sign that the Nile River was also about to rise. Ancient Greeks believed its presence int the sky would adversely affect dogs around the same time, hence the dog days of summer.

Given its status as a fixture in the night sky, Sirius being blocked out — even for a moment — may have been cause for concern among those ancient cultures. Modern-day astronomers, however, know what's happening, and it's an occultation, the name for when one celestial object passes in front of another.

An illustration of 4388 Jürgenstock's path across the night sky
This map shows 4388 Jürgenstock's path across the night sky and where it will cross in front of Sirius. Tomruen/Wikimedia Commons

And that's exactly what will 4388 Jürgenstock will do. First observed in 1964, 4388 Jürgenstock is a 3.1-mile-wide (5 kilometer) asteroid from the asteroid belt that completes an orbit around the sun every three years and seven months. This year, as part of its orbit, it will glide directly in front of Sirius for an estimated 0.2 seconds, though Sirius' full brilliance will take 1.8 seconds to recover.

"This is the first occultation of Sirius ever predicted," David W. Dunham from International Occultation Timing Association, Middle East section, told Forbes. "The star catalogs and asteroid ephemerides were not accurate enough to predict such events before 1975, so nobody tried to predict such occultations before those years."

According to Dunham, Sirius is far from where many asteroids roam, making this occultation something particularly special.

The chances of seeing it, however, are small. The occultation will occur on Feb. 18, at around 10:30 p.m. U.S. Mountain Standard Time, the time zone where the occultation will be visible. Making it even more difficult is that the occultation will only be visible along "a narrow path from the southern tip of Baja California to the Las Cruces–El Paso region, up through the Great Plains, and north to the Winnipeg area," according to Sky and Telescope.