The Big Dipper

The Big Dipper, called the Plough in Britain, is seven bright stars in the shape of a ladle. It is not a constellation: it is an asterism, a pattern inside Ursa Major. It is also the most useful signpost in the northern sky.

Where is it from where I am?

How to spot it: Seven bright stars in the shape of a ladle. Source (opens in a new tab)

An asterism, not a constellation

The IAU's 88 constellations (opens in a new tab) are regions covering the whole sky. Asterisms (opens in a new tab) are familiar patterns that are not constellations. The Dipper's seven stars are the rump and long tail of the Great Bear, Ursa Major, most of whose other stars are much fainter.

A signpost

The two stars at the end of the bowl point to Polaris (opens in a new tab), the North Star. Follow the curve of the handle instead and you arc to Arcturus (opens in a new tab), then on to Spica. The National Park Service (opens in a new tab) records that people escaping slavery in the United States used the Dipper, which some called the drinking gourd, to find the North Star.

Many names

The Romans saw seven plough oxen, Septentrio; Germanicus (opens in a new tab) called the stars a plough because of the shape. In the Chinese Book of Poetry, a poem complains that the Ladle (opens in a new tab) in the north "lades out no liquor", raising its handle in the west.

Where on Earth, and when

The whole key pattern rises from anywhere north of about 28°S.

South of about 41°S, none of it rises.

North of about 41°N, the whole key pattern never sets.

Its middle climbs at least 20° high, the finder's threshold for a suggestion, from anywhere north of about 14°S.

It is highest in the evening sky, at about 9 p.m. local time, in mid-May, from either hemisphere, wherever it rises. With daylight saving time, that is nearer 10 p.m. on the clock.

Worked out by this site from the Bright Star Catalogue, for a flat, clear horizon. Hills, buildings, haze and city light all cut into this; the air also lifts objects near the horizon by about half a degree. For your own place and night, use the sky finder.