Why the moon's Aldebaran occultation all that spooky

Late Tuesday night, the star Aldebaran appeared to vanish, as the moon passed directly in front of it.

Steve Gooch/The Oklahoman/AP
The 'hunter's moon' rises behind a wind farm west of Minco, Okla., Sunday, Oct, 16, 2016.

Just shy of Halloween, the moon has completed a strange cosmic ritual with the eye of Taurus.

Late Tuesday night, the star Aldebaran, the fiery eye of the bull constellation, was occulted by the moon. Occultations, in astronomical terms, occur when one celestial body passes between Earth and another cosmic object, hiding the latter from view.

Spectators in the eastern half of the United States could view the cosmic event through simple telescopes. As the waning gibbous moon moved across the sky, Aldebaran disappeared behind it. Later, having passed through the moon’s dark limb, the star appeared to materialize out of thin air.

Lunar occultations are relatively common, as any bright star with an ecliptic latitude of less than 6.5 degrees may cross the moon’s path. In addition to Aldebaran, first-magnitude stars Regulus, Spica, and Antares are regularly occulted.

Aldebaran, or Alpha Tauri, lies some 65 light years away from Earth, forming the bright eye of the constellation Taurus. Despite its lower surface temperature, this orange giant is over 150 times brighter than our sun and almost 40 times wider, EarthSky notes:

Aldebaran is the 14th brightest star, but five of those that outshine it are only barely visible or not visible at all from much of the Northern Hemisphere. Aldebaran is primarily a winter and spring star. At least, that is when this red star is most easily visible in the evening sky.

Occultations of specific stars occur in cycles. The current Aldebaran “series” began in January 2015 with an occultation visible from the Arctic regions. Stargazers in parts of North America and Hawaii will see another on Dec. 12-13, and a fourth Aldebaran occultation will occur in September 2018. The next Aldebaran series won’t begin until August 2033, Space.com reported.

Planetary occultations are more rare, and a bit more spectacular than their lunar counterparts. In the time between 1702 and 2016, there have only been nine. The most recent occurred in 1818, when Venus passed in front of Jupiter. The two planets won’t meet again until Earth’s next occultation show – in 2065.

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