Ursa Major
What is Ursa Major?
Constellations· Spring evenings (N, circumpolar) · the Big Dipper. The large constellation that contains the Big Dipper. Carry the gap between the two stars at the end of the bowl onward five times and it leads to Polaris, which makes this the usual starting point for finding north.
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Stars of the figure
| Star | Magnitude |
|---|---|
| Dubhe | 1.8 |
| Alioth | 1.8 |
| Alkaid | 1.9 |
| Mizar | 2.2 |
| Merak | 2.4 |
| Phecda | 2.4 |
| Psi Ursae Majoris | 3.0 |
| Talitha | 3.1 |
The 8 brightest of the 18 stars used in the figure (18 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | spring; circumpolar |
|---|---|
| Landmark | the Big Dipper |
| How to find | the seven-star dipper shape |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Five Dipper stars from one family — the Ursa Major Moving Group
Five of the Big Dipper's seven stars did not gather by chance. They were born together from the same cloud of gas about 400 million years ago and still move through space in the same direction. The group is called the Ursa Major Moving Group. Its core lies about 80 light-years away, making it the nearest cluster-like group of stars to the solar system.
The two end stars, Dubhe and Alkaid, are not members. They are farther away and move in very different directions from the other five. Over tens of thousands of years the handle will bend more and the bowl will open wider. The dipper shape we see today is an arrangement that exists only for a while, in our own era, as the stars drift past one another.
The constellation in depth
Ursa Major is best known for the Big Dipper, but the Dipper is not the whole constellation. It is only the bear's hindquarters and tail. Add the head and four legs and Ursa Major becomes the third largest of the 88 constellations, so anyone who knows only the Dipper has seen less than half of it.
The two stars at the end of the bowl, Merak and Dubhe, are called the Pointers. A line drawn from Merak through Dubhe, carried on about five times its length, reaches Polaris. Because Polaris stays almost still in the north all night, people have used this trick to find north for thousands of years.
North of latitude 41 degrees the Big Dipper never sets. From London it never sets; from New York, at 40.7 degrees, it skims the northern horizon on autumn evenings but can be seen all year. From Sydney it never rises fully. Because it circles Polaris, the Dipper stands upright in one season and lies on its side in another. Running the clock in the Sky view shows the Dipper wheeling around Polaris.
Next to Mizar, the middle star of the handle, sits the faint star Alcor. Seeing the two as separate stars with the naked eye has long served as an eyesight test. A telescope splits Mizar into two stars, and splitting their light into its colours shows that each of those is a pair as well. Alcor has a companion too, so six stars in all belong to this one group.
Frequently asked
- When can I see Ursa Major?
- Ursa Major is best seen in spring; circumpolar.
- How do I find Ursa Major?
- To find Ursa Major, look for the seven-star dipper shape.
- What is the brightest star in Ursa Major?
- The brightest star in Ursa Major is Dubhe, at magnitude 1.8.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.