Astronomy EssentialsBrightest Stars

Aldebaran is the Bull’s fiery eye

Sky chart showing an arrow from Orion's Belt to the star Aldebaran.
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.

The reddish star Aldebaran – fiery eye of the Bull in the constellation Taurus – is easy to find. It’s part of a V-shaped star grouping that forms the Bull’s face. This pattern is called the Hyades. You can locate Aldebaran using the famous constellation Orion as a guide. Notice the three stars of Orion’s Belt. Then draw an imaginary line through the belt to the right. The first bright star you come to will be Aldebaran with its distinctive reddish-orange glow.

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.

By the way, although it appears among them, Aldebaran is not actually a member of the V-shaped Hyades cluster. It is actually much closer to us in space than the other Hyades stars.

Read more about the Hyades: Face of Taurus

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Antique etching of front half of a bull superimposed over a star chart.
View larger. | Constellation Taurus. See Aldebaran marked as the Bull’s Eye?

History and mythology of Aldebaran. Aldebaran is often depicted as the fiery eye of Taurus the Bull. Because it is bright and prominent, Aldebaran was honored as one of the Four Royal Stars in ancient Persia, the other three Royal Stars 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. The latter was often viewed as a flock of birds, perhaps doves. According to Richard Hinckley Allen in his classic book “Star Names: Their Lore and Meaning,” the name Aldebaran once was applied to the entire Hyades star cluster, a large loose collection of faint stars.

In Hindu myth, Aldebaran was sometimes identified with a beautiful young woman named Rohini, disguised as an antelope and pursued by her lecherous father, disguised as a deer, Mriga. Apparently several 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. Allen notes a number of other alternate names, but precious little mythology is known for Aldebaran separately.

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

On a different note, 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.

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

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

Aldebaran is an aging star and a huge star! The computed diameter is between 35 and 40 solar diameters. If Aldebaran were placed where the sun is now, its surface would extend almost to the orbit of Mercury.

Science of Aldebaran. 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 4000 kelvins (about 3700 degrees C or 6700 degrees F) compared to 5800 kelvins (about 5500 C or 10,000 F) for the sun.

Aldebaran is about 65 light-years away, much closer than the stars of the Hyades with which it misleadingly seems associated. The Hyades are about 150 light-years away.

Aldebaran is an erratic variable with minor variations too small to be noticed by 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”

Bottom line: The star Aldebaran is so huge that, if it were in our sun’s place, its surface would extend almost to the orbit of Mercury.

December 5, 2019
Astronomy Essentials

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