Meet Elnath in the Horn of the Bull

The Vitals

Official name	Elnath
Other designations	El Nath, Alnath, Beta Tauri, HR 1791, HIP 25428, HD 35497
Nicknames	-
Apparent magnitude	1.65
Distance from Earth	134 light-years
Type	B7 III
Color	Blue
Mass	4.2 M☉
Radius	4.6 R☉
Constellation	Taurus
Right ascension	05h 26m 17s
Declination	+28° 36' 26"
Multiple system?	No
Variable star?	No
Exoplanets status	None known
Probable fate	Planetary nebula

Physical Characteristics

Taurus offers plenty to keep astronomers busy. Besides bright Aldebaran and the Pleiades, there’s the famous Crab Nebula, the Hyades star cluster, and the annual Taurids meteor shower. Given these wonders, we wouldn’t blame you if you haven’t stopped to explore Elnath, the constellation’s second brightest star. But you should. It’s a unique star with some interesting attributes. 

Elnath is technically classified as a giant star, but this isn’t a monster in the league of Betelgeuse or Rigel. It’s only 4 to 5 times larger than the Sun. Nevertheless, Elnath pours out a phenomenal amount of energy, shining with a brightness 500 times the Sun’s luminosity. From Earth’s distance, it’s the 25th brightest star in the night sky. Elnath is hot and has a correspondingly blue color.

Perhaps the most interesting aspect of Elnath is its peculiar chemical composition. Elnath, like the Sun, is mostly hydrogen and helium, but it has 25 times more magnesium than the Sun does. At the same time, compared to solar values, it has eight times less calcium and manganese. There’s a kind of chemical diffusion happening in these stars, causing atoms of some elements to rise and others to fall deeper within the star.

Because of this, mercury-manganese stars like Elnath sometimes exhibit chemical spots, where the chemical composition differs from the rest of the surface. This phenomenon is different from the dark sunspots we see on the Sun, generated by solar magnetic fields.

Origin / Mythology

While many of the current constellations have a Greek origin, many individual star names come from the Arabic tradition. Elnath is one of these. The name, which in Arabic means “butting” or “goring” and is a direct reference to the Bull’s horns, provides the viewer with context for imagining Taurus. (The constellation typically represents only the front half of the Bull).

Many Northern Hemisphere constellations are ancient, but Taurus is particularly so, with some associated Mesopotamian myths dating back 4,000 years or more. One ancient painting of a bull in the Lascaux caves in France might actually be a rendition of Taurus, with six dots above its back representing the Pleiades. If this interpretation of the ancient painting is correct, than humans may have been connecting Elnath with Taurus’ horns for even longer than the written Mesopotamian records.

How to See Elnath

Taurus is conveniently located for evening viewing in the fall and winter, northwest of Orion and crowned by the vividly red Aldebaran. If Aldebaran is imagined to be the Bull’s eye, Elnath is the tip of its left horn (on our right), forming a deep “V” shape with Aldebaran and the fainter Tianguan (Zeta Tauri).

Elnath is near the galactic plane, almost exactly opposite the sky from Sagittarius, in a sparse location known as the galactic anticenter. By the time spring arrives, Taurus fades away into the glare of the Sun, reappearing on the other side the following autumn.

Stargazers who know their constellations will notice that Elnath is pretty close to Auriga (that charioteer holding those goats). Constellation boundaries are dynamic, changing over the course of history. The ancient astronomer Ptolemy included Elnath as part of Auriga, and in those days Elnath was sometimes referred to as Gamma Aurigae. 

Taurus is a zodiac constellation, and thus visited frequently by the Moon, planets, and during the summer, the Sun. Stay on the lookout for these visitors.

When gazing up at the night sky it’s fun to remember that many of those points of light are stars that are similar to our own Sun. But Elnath provides the opportunity to imagine a different type of Sun — one bluer, with a quieter atmosphere, and made of somewhat different materials. What might it look like close up? Even if you can’t go there to see, there’s nothing stopping you from exploring Elnath from a distance tonight. What are you waiting for? Step outside, and take the Bull by the horns.

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Daniel Johnson is a Wisconsin-based freelance writer and professional photographer and the co-author of over a dozen books. He’s a longtime amateur astronomer and fortunate enough to live in a rural region with excellent seeing conditions. You can view some of Dan’s photography (he does a lot of animals!) at foxhillphoto.com

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