2020 Guide to the Night Sky. Storm Dunlop

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The Northern Circumpolar Constellations

      The northern circumpolar stars are the key to starting to identify the constellations. For anyone in the northern hemisphere they are visible at any time of the year, and nearly everyone is familiar with the seven stars of the Plough – known as the Big Dipper in North America – an asterism that forms part of the large constellation of Ursa Major (the Great Bear).

       Ursa Major

      Because of the movement of the stars caused by the passage of the seasons, Ursa Major lies in different parts of the evening sky at different periods of the year. The diagram below shows its position for the four main seasons. The seven stars of the Plough remain visible throughout the year anywhere north of latitude 40°N. Even at the latitude (50°N) for which the charts in this book are drawn, many of the stars in the southern portion of the constellation of Ursa Major are hidden below the horizon for part of the year or (particularly in late summer) cannot be seen late in the night.

       Polaris and Ursa Minor

      The two stars Dubhe and Merak (α and β Ursae Majoris, respectively), farthest from the ‘tail’ are known as the ‘Pointers’. A line from Merak to Dubhe, extended about five times their separation, leads to the Pole Star, Polaris, or α Ursae Minoris. All the stars in the northern sky appear to rotate around it. There are five main stars in the constellation of Ursa Minor, and the two farthest from the Pole, Kochab and Pherkad (β and γ Ursae Minoris, respectively), are known as ‘The Guards’.