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Moon near Aldebaran on February 23

At top: Bright star Aldebaran on the moon’s dark edge, just before the moon passed in front of this star on March 4, 2017. Photo by Michael Caruso in Morgantown, West Virginia.

February 23, 2018 finds the moon near Aldebaran again. The moon and star will be especially close together as seen from Europe and Asia.

In fact, if you live at just the right spot on Earth, you can watch the moon occult – cover over – Aldebaran for a portion of the night on February 23, 2018. The star will disappear behind the dark side of the moon and reappear on its illuminated side.

For instance, if you live in Moscow, Russia, the lunar occultation of Aldebaran will happen from 8:30 p.m. to 9:33 p.m., local time (the time on your clock if you’re in Moscow). You can actually watch the occultation of Aldebaran if you’re at a northerly latitude in eastern Europe and Asia. If that’s you, Aldebaran will disappear behind the moon’s dark side and then reappear on the moon’s illuminated side.

See the worldwide map below for more details.

Worldwide map via IOTA. Every place north of (above) the curved white line sees the February 23 occultation of Aldebaran in a nighttime sky. Places to the north of the short blue line see the occultation at evening dusk. For places to the north of the red line, the occultation happens in a daytime sky. Click here to find out the Universal Time of the occultation for over a thousand localities. You must convert Universal Time to your local time. Here’s how.

The sky chart below shows the moon and Aldebaran as they’ll appear from middle North American latitudes on February 22, 23 and 24.

From North America, we’ll see the moon to the east of Aldebaran on February 23.

If you live in the world’s Eastern Hemisphere – Europe, Africa, Asia, Indonesia, Australia and New Zealand – you’ll see the moon offset in the direction of Aldebaran, or to the west of Aldebaran, on February 23.

The moon moves eastward through the constellation Taurus the Bull for several days each month. When the moon moves out of this region of sky, use Orion’s Belt to locate the star Aldebaran and the Pleiades star cluster.

Of course, no matter where you are on Earth, the moon and Aldebaran only appear close together as seen on our sky’s dome. They aren’t really close together in space. The moon, our closest celestial neighbor, is about 230 thousand miles (371 thousand km) from Earth on February 23. Aldebaran lies 65 light-years away. One light-year is about 25 million times the distance of the February 23 moon. That places Aldebaran at about 1.6 billion times the moon’s distance. Wow!

Aldebaran only looks small next to the moon because this red giant star resides so far away. If Aldebaran replaced the sun in our sky, its diameter would span about 20 degrees of our sky. That’s 40 times the diameter of our sun, which covers about 1/2 degree of sky!

How do we know? Lunar occultations of Aldebaran – like the February 23 occultation – have enabled astronomers to measure the angular diameter of this star and to estimate its physical diameter at around 40 solar diameters.

Contrast the size of giant Aldebaran with our sun. Image via Wikipedia.

By the way, we’re in the midst of a series of 49 monthly occultations of Aldebaran that began on January 29, 2015, and will conclude on September 3, 2018.

Bottom line: On February 23, 2018, look for the moon near Aldebaran, the ruddy eye of the Bull in the constellation Taurus. From northerly latitudes in eastern Europe and Asia, the moon will occult (cover over) Aldebaran. The star will disappear behind the moon’s dark side and then reappear on the moon’s illuminated side.

Bruce McClure

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