Aldebaran vs Arcturus
Two orange K-type giants, similar in colour and dissimilar in almost everything else an observer measures. Arcturus reaches magnitude −0.05 and Aldebaran 0.87, a 0.92-magnitude gap amounting to about 2.3 times the light. Distance explains most of it: Arcturus lies 36.72 light-years away, Aldebaran 66.64, nearly twice as far. Their absolute magnitudes of −0.31 and −0.68 in fact favour Aldebaran by a modest 1.4 times, so the fainter-looking star is marginally the more luminous. The pair also sit on opposite sides of the observing year, which is why they are rarely compared directly in the sky.
Property comparison
| Property | Aldebaran | Arcturus |
|---|---|---|
| Designation | 87Alp Tau | 16Alp Boo |
| Constellation | Taurus | N/A |
| Spectral Class | Class K — K-type (Orange) | Class K — K-type (Orange) |
| Apparent Magnitude | +0.87 | -0.05 |
| Absolute Magnitude | -0.68 | -0.31 |
| Distance | 66.6 ly | 36.7 ly |
| Mass | N/A | N/A |
| Radius | N/A | N/A |
| Temperature | N/A | N/A |
| Luminosity | N/A | N/A |
Full data for each star: Aldebaran · Arcturus
Key differences
Key Differences
- ◆ Both are orange K-type giants that have evolved off the main sequence.
- ◆ Arcturus is the brightest star in the northern celestial hemisphere at magnitude −0.05.
- ◆ Aldebaran is larger at ~44 R☉ versus Arcturus at ~25 R☉.
- ◆ Arcturus is much closer at 36.7 light-years; Aldebaran is about 65 light-years away.
- ◆ Arcturus has an unusually high proper motion and may be a remnant of a disrupted dwarf galaxy.
When to Observe
Aldebaran
Arcturus culminates at midnight in late April and commands the spring and early-summer evening sky. At declination +19° it rises high for northern observers and remains accessible well into the southern hemisphere.
Arcturus
Aldebaran culminates at midnight in late November, six months out of phase with Arcturus, and belongs to the winter evening sky. Its declination of +16° gives it a similar reach.