Aldebaran, Bull’s bloodshot eye, near moon December 15, 16, 17

A chart showing the moon moving past Aldebaran. Aldebaran is in the middle, Orion is below it, the Pleiades is above. The moon is between the Pleiades and Aldebaran during December 15, 16 and 17.
The bright waxing gibbous moon will be near the star Aldebaran in the night sky on December 15, 16 and 17, 2021. You’ll be able to pick out this red star in the moon’s glare. Chart by John Jardine Goss.

Look for red star Aldebaran – fiery eye of the Bull in the constellation Taurus – near the moon on December 15, 16 and 17, 2021. Aldebaran is part of a V-shaped group of stars – the Hyades – that forms the Bull’s face. But you likely won’t see the Hyades in the moon’s glare. Still, you can confirm it’s Aldebaran you’re seeing, using the famous constellation Orion as a guide. Notice the three stars of Orion’s Belt. Then draw an imaginary line through the belt. The first bright star you come to will be Aldebaran with its distinctive red-orange glow.

Although Aldebaran is associated with the stars of the Hyades – Face of the Bull in Taurus – it’s not really part of this V-shaped star pattern. Aldebaran is much closer at 65 light-years than the Hyades stars, which are an open star cluster – a true family of stars in space – about 150 light-years away.

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When to spot Aldebaran

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 for us on the northern part of Earth. That’s when this red star is most easily visible in the evening sky. By early December, it rises shortly after sunset and is visible all night. Three months later it is high to the south at sunset and sets at around midnight. By early May, it hangs low about the western sunset glow – and before the end of the month, it’s lost altogether. It returns to the predawn sky around late June.

Sky chart showing an arrow from Orion's Belt to the star Aldebaran. The Pleiades is in the upper right.
If you can find the prominent constellation Orion, you can find the bright red star Aldebaran. Orion’s Belt always points to Aldebaran. Extending that line takes you generally toward the Pleiades, or Seven Sisters. Look east in mid-evening in December. Check Stellarium for the view at your location.

History and mythology of Aldebaran

Artists often depict Aldebaran as the fiery eye of Taurus the Bull. Because it is bright and prominent, ancient Persians honored Aldebaran one of the Four Royal Stars, the other three being Regulus, Antares and Fomalhaut.

The name Aldebaran is from the Arabic for the follower, presumably as a hunter following prey, which here likely was the star cluster we call the Pleiades. Some viewed the latter as a flock of birds, perhaps doves. According to Richard Hinckley Allen in his classic book Star Names: Their Lore and Meaning, people once applied the name Aldebaran to the entire Hyades star cluster, a large loose collection of faint stars. Allen notes a number of other alternate names, but precious little mythology is known for Aldebaran separately.

In Hindu myth, Aldebaran was a beautiful young woman named Rohini, disguised as an antelope and pursued by her lecherous father, disguised as a deer, Mriga. Several other ancient peoples associated the star with rain. The Wikipedia entry notes a Dakota Sioux story in which Aldebaran was a star which had fallen to the Earth and whose killing of a serpent led to the formation of the Mississippi River.

Astronomer Jack Eddy has suggested a connection with the Big Horn Medicine Wheel, an ancient circle of stones atop a mountain in Wyoming. Eddy wrote that the ancient Americans may have used this site as a sort of observatory to view the rising of Aldebaran just before the sun in June to predict the June solstice.

Aldebaran is the name of one of the chariot horses in the movie and book “Ben Hur.”

Interestingly, in about two million years, the NASA space probe Pioneer 10, now heading out into deep space, will pass Aldebaran.

Antique etching of front half of a bull superimposed over a star chart with Aldebaran written on its face.
View larger. | The constellation Taurus. See Aldebaran marked as the Bull’s Eye? Image via Wikipedia.

Science of Taurus’ brightest star

Aldebaran is an aging, huge star. The diameter is between 35 and 40 times the size of our sun. If Aldebaran replaced our sun, its surface would extend almost to the orbit of Mercury.

This star glows with the orangish color of a K5 giant star. In visible light, it is about 153 times brighter than the sun, although its surface temperature is lower, roughly 4,000 kelvins (about 3,700 degrees C or 6,700 degrees F) compared to 5,800 kelvins (about 5,500 C or 10,000 F) for the sun.

Aldebaran is an erratic variable with minor variations too small to see with the eye. It also has a small, faint companion star, an M-type red dwarf, some 3.5 light-days away. In other words, light from Aldebaran would need to travel for 3.5 days to reach the companion, in contrast to light from our sun, which requires 8 minutes to travel to Earth.

Aldebaran’s position is RA: 4h 35m 55s, dec: 16°30’35”

Part of huge orange circle with little yellow circle beside it labeled sun.
A comparison of the size of Aldebaran with our sun. Image via Wikipedia.

Bottom line: Aldebaran is an enormous, reddish-colored star that marks one of the eyes of Taurus the Bull. It marks one point of the V-shape of the Bull’s face.

December 15, 2021

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