Phecda (Gamma Ursae Majoris)
Phecda (Gamma Ursae Majoris) is a star in the constellation Ursa Major, magnitude 2.4.
The Dipper’s spinning corner — a white star whose poles run thousands of degrees hotter than its equator.
Phecda is the thigh of the Great Bear — its name comes from the Arabic fakhth al-dubb, “thigh of the bear”. Hindu astronomers knew it as Pulastya, one of the Seven Rishis.
It is a white star 2.4 times the Sun’s mass and about 333 million years old, spinning at some 386 km per second at its equator. The spin flattens it: its equator is about half as wide again as its poles. The poles, near 10,500 kelvin, are far hotter than the equator, near 6,750. A shell of gas around it adds bright emission lines to its spectrum.
Phecda has a hidden partner, a smaller orange star of about 0.8 solar masses whose pull makes it wobble every 20.5 years. It is also part of a real family: with four other Dipper stars it belongs to the Ursa Major moving group, and it lies fairly close in space to Mizar and Alcor.
Phecda (Gamma Ursae Majoris) is 83 light-years away: the light we see from it set off in 1943, 13 years after Pluto was discovered.
Did you know?
- A standard since 1943. Phecda’s spectrum has served since 1943 as one of the stable reference points by which astronomers sort other stars into classes.
- Celestial Shining Pearl. In China it is Tiān Jī, the Star of Celestial Shining Pearl, and the third star of the Northern Dipper.
A white 2nd-magnitude star at the corner of the Big Dipper’s bowl diagonally opposite Dubhe, next to the handle. Compare the two: white against orange.
When and where to see it
It is best placed in the evening sky around April, when it crosses the meridian at about 10 pm local time (around midnight in March). It can be seen from everywhere north of 36°S and never sets north of 36°N.
At its highest it stands 86° up from 50°N, 71° up from 35°N, 36° up from the equator, 1° up from 35°S.
Facts
- Type
- Star
- Constellation
- Ursa Major
- Designations
- Gamma Ursae Majoris, γ UMa, 64 UMa, HR 4554, HD 103287, HIP 58001
- Magnitude
- 2.4
- Position
- RA 11h 53.8m, Dec +53° 42′ (J2000)
- Spectral type
- A0V
- Colour
- white (B−V 0.01)
- Distance
- 83 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Phecda (Gamma Ursae Majoris) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.