Mirach (Beta Andromedae)
Mirach (Beta Andromedae) is a star in the constellation Andromeda, magnitude 2.0.
The red giant at Andromeda’s hip — and the classic signpost to the Andromeda Galaxy.
Mirach’s name is a copying slip. The Arabic mīzar, “girdle”, was garbled to mirat in a Latin translation of Ptolemy’s Almagest, and the Alfonsine Tables of 1521 described the star as super mizar. The girdle sits at the left hip of the chained princess Andromeda.
It is a red giant late in its life, about two and a half times the Sun’s mass. With the hydrogen in its core long gone, it has bloated to some 86 times the Sun’s width and shines nearly 1,700 times as brightly. It may vary slightly, and a 2023 study found hints of a brown dwarf circling it.
Since 1943 its spectrum has been one of the anchor points for classifying other stars. Chinese astronomers used it as their standard “black” star — in this sense a deep red, set against Antares, the standard red.
Mirach (Beta Andromedae) is 200 light-years away: the light we see from it set off around 1825, 20 years before Neptune was discovered.
Did you know?
- Mirach’s Ghost. Just seven arcminutes from Mirach lies the small galaxy NGC 404, nicknamed Mirach’s Ghost for the way it hovers in the bright star’s glare.
- The Porpoise. In Micronesia the star was Kyyw, “the Porpoise”, and the name also served for one of the months.
- The Deleter. The Babylonian star catalogue MUL.APIN lists it as KA.MUSH.I.KU.E, “the Deleter”.
A red-orange 2nd-magnitude star, the middle of three bright stars that curve north-east from the Great Square of Pegasus. Hop north-west from it through Mu and Nu Andromedae to reach the Andromeda Galaxy; the faint galaxy NGC 404 sits right beside Mirach.
When and where to see it
It is best placed in the evening sky around November, when it crosses the meridian at about 10 pm local time (around midnight in October). It can be seen from everywhere north of 54°S and never sets north of 54°N.
At its highest it stands 76° up from 50°N, 89° up from 35°N, 54° up from the equator, 19° up from 35°S.
Facts
- Type
- Star
- Constellation
- Andromeda
- Designations
- Beta Andromedae, β And, 43 And, HR 337, HD 6860, HIP 5447
- Magnitude
- 2.0
- Position
- RA 1h 9.7m, Dec +35° 37′ (J2000)
- Spectral type
- M0+IIIa
- Colour
- orange-red (B−V 1.57)
- Distance
- 200 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Mirach (Beta Andromedae) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.