Mensa
What is Mensa?
Constellations· Southern summer · directly south of the Large Magellanic Cloud. Lacaille named it after Table Mountain in Cape Town, where he made his observations. Its brightest star is only fifth magnitude — the faintest of any constellation — but part of the Large Magellanic Cloud drapes over it like the mountain's famous 'tablecloth' cloud.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Mensa is in your sky right now: https://nowsky.org/solar/sky?sel=con:Mensa — location and time set automatically, no login.
Stars of the figure
| Star | Magnitude |
|---|---|
| Alpha Mensae | 5.1 |
The 1 brightest of the 3 stars used in the figure (2 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | Dec–Feb evenings; never visible from Korea |
|---|---|
| Brightest star | α Mensae, mag 5.1 — faintest alpha star of any constellation |
| How to find | south of the Large Magellanic Cloud, toward the pole |
| Area rank | 75th of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- When can I see Mensa?
- Dec–Feb evenings; never visible from Korea.
- How do I find Mensa?
- south of the Large Magellanic Cloud, toward the pole.
- What is the brightest star in Mensa?
- Alpha Mensae, magnitude 5.1.
- Where is Mensa in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
Chandra's first target — a quasar jet in Mensa
In August 1999 one of the first objects Chandra pointed at from orbit was the quasar PKS 0637-752, six billion light-years away in the direction of Mensa. It was a test observation for focusing the telescope, and something unexpected appeared in it: a jet 200,000 light-years long streaming from the quasar, shining brightly in X-rays.
A jet known until then only from radio had no obvious reason to be so bright in X-rays, and a new explanation was proposed — electrons in the jet kicking photons of the cosmic microwave background up to X-ray energies. The result was recorded among Chandra's discoveries of its first month, and dozens of quasar jets have since been observed the same way. In the constellation whose chief star is the faintest of the 88, a new chapter of X-ray astronomy opened.
The constellation in depth
Mensa is the only one of the 88 constellations named after a real place on Earth: Table Mountain in Cape Town, beneath which Lacaille charted the southern sky in 1751–52. He chose a spot where the Large Magellanic Cloud hangs over the stars, recalling the white cloud that often settles on the mountain. Its original name was simply Mons Mensae, the Table Mountain.
Alpha Mensae shines at only magnitude 5.1, the faintest 'alpha' star of any constellation. It is a Sun-like star 33 light-years away with a red-dwarf companion, and pi Mensae hosts both a planet ten times Jupiter's mass and a small super-Earth — an early success of the TESS satellite. The southern edge of the Large Magellanic Cloud spills into the constellation. It is the only constellation whose brightest star is fainter than fifth magnitude.
At declinations of −70° to −85° it can never be seen from the northern hemisphere, while in the south it never sets. Look directly south of the Large Magellanic Cloud toward the pole on December to February evenings. In the Sky view, set Cape Town on a January evening and check below the Cloud. Keep the constellation lines on; its stars are the faintest of any constellation.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.