When is the best time to observe Tejat Posterior?

Tejat Posterior is best observed from November through January, with peak visibility during December when it transits around midnight in the Northern Hemisphere.

Where is Tejat Posterior located in the sky?

Tejat Posterior lies in the constellation Gemini at right ascension 06h 23m and declination +22° 31′.

What telescope do I need to split Tejat Posterior?

Splitting Tejat Posterior requires an aperture of roughly 60 mm or larger — the components are separated by about 58.7″ at magnitudes near 2.9. The companion is about 9.0 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Tejat Posterior — Double Star in Gemini

HIP 30343; Mu Geminorum; 13 Geminorum

Magnitude 2.8–3.0^m DoubleStar Gemini (Gem) Visible

Star Map + List + Plan

About Tejat Posterior

Description

Tejat Posterior is a deep-red giant of spectral type M3IIIab at magnitude 2.88 in Gemini. Located about 232 light-years from Earth, it has a luminosity of roughly 1,148 times solar. It is a semi-regular variable star, varying between about magnitude 2.75 and 3.02, and is one of the reddest naked-eye stars in the winter sky.

Observing Tips

Tejat Posterior lies at the foot of the northern Twin (Castor's foot) in Gemini. Its deep orange-red color is striking in binoculars and provides a vivid contrast with the many white and blue stars of the winter sky. Compare its color with the nearby Propus (Eta Gem). Best observed December through April.

History

The name Tejat Posterior means 'the back foot,' from Arabic and Latin, referring to its position at the Twin's foot. The semi-regular variability was first noted in the 19th century.

Fun Facts

Tejat Posterior is one of the reddest stars visible to the naked eye in the winter sky, with a B-V color index of 1.64. Its deep color results from its cool 3,500 K surface temperature — the star is a highly evolved giant approaching the end of its life.

Observe

1Physical Properties

Magnitude 2.88

Range 2.75 - 3.02

Period 17.4 hours

Variable Type Semi-Regular Variable

Spectral Type M3IIIab bright giant

Star Color Red (B-V 1.64)

Distance 231 ly

2Position & Identifiers

RA 06h 22m 57.6s

Dec +22° 30' 49.0"

Constellation Gemini (Gem)

HR 2286

HIP 30343

HD 44478

SAO 78297

Bayer Mu

Flamsteed 13 Gem

Variable ID Mu Gem

Double Cat 4990

SIMBAD Wikipedia

3How easy to split?

Primary 2.9 mag Companion 11.9 mag Separation 58.7″

Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Hard	V. hard+	V. hard
150 mm Newton 150mm Newt.	Medium	Hard+	Hard
Celestron C8 (203 mm SCT) C8 203mm	Medium+	Medium	Hard+

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

Set a location in User Settings to see visibility data.

Best season Nov – Jan (peak: Dec)

5Light Curve

6Multiple Star System Triple D,E,F: optical

Components 3 (triple)

Component IDs AxBC

Separation 58.7″

Companion Mag 11.9

Position Angle 65°

Star Colors A: Red

Discoverer BU 1059

Separation over time

Measured 1831 → 2007 (176 y)

Separation drift 80.0" → 58.7" (-21.30")

Rate -0.1210" / y

PA drift 89° → 65° (-24°, -0.136°/y)

Apparent motion is significant on a human timescale — worth revisiting in a decade.

Measured from the WDS observational archive. No orbital solution has been derived — most likely the period is too long to fit an orbit to the available measurement arc.