Collins Night Sky. Wil Tirion

night a large number of fainter stars surround the five main stars, and this may sometimes make identification slightly more difficult for beginners. Even when the Milky Way is not readily visible because of moonlight or light pollution, some people are still occasionally confused by the presence of the moderately bright stars, η and κ Cas. With just a little practice, however, Cassiopeia becomes easy to recognize.

      CEPHEUS

      Although the constellation of Cepheus is circumpolar, it is not nearly as well known as Ursa Major, Ursa Minor or Cassiopeia. This is partly because it does not form a highly distinct pattern on the sky, and also because some of its stars are faint. Its shape is often likened to (and does actually resemble) the gable end of a house, with the ‘ground’ lying in the Milky Way not far from Cassiopeia, and the tip of the gable pointing towards the pole.

      Locating the constellation of Cepheus.

      Its brightest star, α Cephei (Alderamin), lies in the Milky-Way region, at the ‘bottom right-hand corner’ of the figure. A line from α to β Cassiopeiae (Shedir to Caph), extended about three times the separation, passes just north of Alderamin. The star at the tip of the ‘gable’, γ Cephei (Errai) lies close to the line from α UMa (Polaris) to β Cas (Caph). The line from the Pointers to Polaris, if extended, also passes just ‘below’ the tip of the ‘gable’.

      DRACO

      The last of the circumpolar constellations that is fairly easy to identify is Draco, although it is so long that it takes a bit of practice to recognize it easily. It consists of a quadrilateral of stars, known, logically enough, as the Head of Draco (and also the ‘Lozenge’), and a long chain of stars forming the neck and body of the dragon.

      Finding the Head of Draco is not particularly easy using just circumpolar stars. Locate the two stars (α and β UMa) at the opposite end of the bowl of the Plough from the Pointers. Extend a line from γ UMa (Phad) through δ UMa (Megrez) by about eight times their separation. This takes you right across the sky below the Guards in Ursa Minor, and close to ξ Dra (Grumium) at one corner of the quadrilateral. The brightest star, γ Dra (Etamin) lies farther to the south. From the head of Draco, the constellation first runs north-east to δ and Dra, then doubles back southwards, before winding its way round between Ursa Minor and Ursa Major, through α Dra (Thuban), before ending at λ Dra (Giansar) almost on the line between the Pointers and Polaris.

      Finding the head of Draco.

      The circumpolar chart shows that there is a large area of sky between Ursa Major and Cassiopeia that has relatively few bright stars. There is one constellation here, Camelopardalis, which is always circumpolar, but which is so faint that it is easier to learn to find it after you have gained some experience, and are familiar with some of the constellations that lie farther south. Large parts of the constellations of Auriga, Cygnus, Lynx, and Perseus are also often circumpolar, depending on your exact latitude. These will be described shortly.

      SEASONAL CONSTELLATIONS

      Although it is generally best to start with the circumpolar constellations when learning the night sky, the visibility of areas farther south depends greatly on the season. Luckily, there are conspicuous, easily recognized constellations visible at every season: Orion, Taurus, Gemini, and Auriga in winter; Leo, Hydra, and Boötes in spring; Cygnus, Lyra, and Aquila in summer; Pegasus and Andromeda in autumn. The limitations posed by summer twilight may cause problems in learning that area of the sky, but the brilliant stars of the Summer Triangle (Deneb, Vega, and Altair) are readily seen and act as guides even in twilight.

WINTER CONSTELLATIONS

      For northern-hemisphere observers, the winter sky is always dominated by the magnificent constellation of Orion. It is readily recognizable, with orange-red Betelgeuse (α Orionis) in the Northeast, brilliant, blue-white Rigel (β Orionis) in the south-west, and the three stars forming the ‘Belt’ in the centre of the constellation.

      The stars of the Belt point down towards Sirius (α Canis Majoris), the brightest star in the sky. The southern part of Canis Major, with δ (Wezen) and (Adhara), is low from most northern latitudes and requires clear skies to be readily seen. West of Canis Major, and beneath Orion, is the small, but distinctive constellation of Lepus. South of that, low on the horizon, Columba may be seen when skies are clear. Farther west, the long, straggling constellation of Eridanus begins close to Rigel and sweeps in a wide arc to the west before plunging below the southern horizon.

      Following the Belt stars in the opposite direction, they point north-west, approximately in the direction of orange Aldebaran (α Tauri) and the nearby ‘V’-shaped cluster of the Hyades. Still farther north-west lies the conspicuous cluster of blue-white stars known as the Pleiades. The rest of the constellation of Taurus is relatively inconspicuous, and the second-brightest star β (Alnath) was once regarded as part of Auriga. The brightest star in Auriga itself, yellowish-white Capella (α Aurigae), is high overhead, near the zenith. The constellation forms a rough pentagon with β Tauri, with a distinctive triangle of stars (known as ‘the Kids’) west of Capella.

       Northwest of Auriga, above the Pleiades, lies Perseus, with no distinct shape, but which essentially consists of three lines of stars, meeting at α Persei (Mirfak). One line runs down towards the south, the second, containing the famous variable Algol towards the south-west, and the third extends away from Taurus and Orion towards Cassiopeia. Southeast of Auriga lies Gemini, with the bright stars Castor and Pollux. Castor (α Geminorum), the northernmost, is the fainter of the two, and may also be found by extending a line from Rigel, at the foot of Orion, through Betelgeuse. Pollux (β Geminorum), lies to the south-east. The rest of the constellation largely consists of two lines of stars that run back from Castor and Pollux towards Orion.

       Forming an approximate equilateral triangle with Betelgeuse and Sirius is Procyon (α Canis Minoris), the single bright star (magnitude 0.4) in an otherwise inconspicuous constellation. More or less centred in the same equilateral triangle is the sprawling, but very faint, constellation of Monoceros.

       The Milky Way runs right across this region of the sky, from Cassiopeia, through Perseus, Auriga, Gemini, Orion, and Monoceros. Although less conspicuous than the dense star clouds that stretch from Cygnus to Sagittarius, it is nevertheless readily seen in dark, clear skies. The swarms of faint stars sometimes make it difficult to pick out the pattern of Monoceros, and beginners occasionally encounter problems in identifying the fainter stars in Perseus for the same reason.

       The northernmost star of Orion’s Belt, Mintaka (δ Orionis) is just slightly to the south of the celestial equator. Trailed photographs of Orion rising in the east show Mintaka’s trail as an almost perfectly straight line, while the trails of stars farther north and south show increasing curvature.

       The Sun reaches its northernmost declination (at the northern summer solstice) just inside the eastern border of Taurus, precession having carried it out of Gemini. If the line of latitude at which the Sun is overhead at the summer solstice were named nowadays, instead of being known as the Tropic of Cancer, it would be the Tropic of Taurus.

      Winter: the bright winter constellations are easy to recognize.

SPRING CONSTELLATIONS

      The most distinctive constellation in the spring sky is Leo, whose brightest star, Regulus (α Leonis) lies extremely close to the ecliptic. When Leo is low in the sky, it may be located by extending the line of the Pointers (α and β Ursae Majoris) in the opposite direction to normal, away from Polaris. Regulus may also be found