# Tejat (Mu Geminorum)

Tejat (Mu Geminorum) is a star in the constellation Gemini, magnitude 2.9.

**A swollen red giant at the Twins’ feet, near the end of its life — with a name whose meaning is lost.**

In its last bright act, Tejat has swollen into a red giant more than 100 times wider than the Sun. Its core has run out of fuel, leaving an inert heart of carbon and oxygen, while hydrogen and helium still burn in thin, nested shells around it. Its surface, at about 3,800 kelvins, is far cooler than the Sun’s, yet the bloated star shines more than 1,500 times as brightly.

Stars at this stage rarely sit still. Tejat drifts in brightness by a few tenths of a magnitude, with a rough 72-day rhythm and a slower swing lasting about 2,000 days, making it a slow, irregular [variable star](https://astropilot.space/glossary/variable-star).

Its name is a mystery. Tejat comes from an old southern Arabic word, tiḥyāt, whose meaning has been lost. Other names have attached themselves over the centuries: Calx, Latin for ‘heel’; Pish Pai, Persian for ‘foreleg’; and Nuhatai, from an Arabic word for a camel’s hump.

Tejat (Mu Geminorum) is 230 light-years away: the light we see from it set off around 1795, 15 years after William Herschel discovered Uranus.

## Did you know?

- **In the Moon’s path.** Tejat lies less than a degree south of the ecliptic, so the Moon sometimes passes in front of it — and, very rarely, a planet does too.
- **A companion that isn’t.** Two arcminutes away lies a faint pair of stars catalogued as Tejat’s companion. They are an unrelated double, far in the background.
- **First Star of the Well.** In Chinese astronomy Tejat leads Jǐng, the Well, an asterism of eight stars in Gemini that includes Alhena.

An orange-red 3rd-magnitude giant at the feet of Castor, with fainter Propus just to its west and the cluster M 35 a little beyond. Its warm tint contrasts with white Alhena to the south-east; watch for slow changes of a few tenths of a magnitude.

## When and where to see it

It is best placed in the evening sky around January, when it crosses the meridian at about 10 pm local time (around midnight in December). It can be seen from everywhere north of 67°S and never sets north of 67°N.

At its highest it stands 63° up from 50°N, 78° up from 35°N, 67° up from the equator, 32° up from 35°S.

## Facts

- Type: Star
- Constellation: Gemini
- Designations: Mu Geminorum, μ Gem, 13 Gem, HR 2286, HD 44478, HIP 30343
- Magnitude: 2.9
- Position: RA 6h 23.0m, Dec +22° 31′ (J2000)
- Spectral type: M3IIIab
- Colour: orange-red (B−V 1.64)
- Distance: 230 light-years
- Discovered: Known since antiquity

Open AstroPilot to see when Tejat (Mu Geminorum) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/tejat