The constellations of Spring are now appearing in the night sky and although quite small and rather dim Cancer is an original Greek constellation. Cancer is located between the stars Castor and Pollux, the bright stars which mark the “Heads of the Twins”, and the “Backward Question Mark” shape which marks “The Head of Leo”. As you can guess astronomers have a vivid imagination. Cancer is a Zodiacal Constellation, the Sun, the Moon and the planets pass through it during their motions. Cancer contains no bright stars; it represents the Crab which crept out of the swamp and nipped Heracles as he fought the monster Hydra, one of his twelve labours. Heracles stamped on the crab and crushed it, but its valiant effort was rewarded by the Goddess Hera, a bitter enemy of Heracles, who placed it in the heavens. There is one object of interest in Cancer which is easily visible using binoculars, Praesepe, also known as the “Beehive Cluster”. is composed of many dim stars arranged in the shape of an old-fashioned conical beehive, complete with a few bees buzzing around it. The famous French astronomer Charles Messier recorded as M44 in his famous catalogue.
Later in the night take a look at the “Plough” asterism, it will be seen standing upright and the “Handle” stars are high above the horizon. If the arc of stars forming the “Plough’s handle” are extended they point to the 4th brightest star in the sky Arcturus. Arcturus is the bright orange coloured lead star of Boötes, The Herdsman. Arcturus is a huge star approximately 25 times the diameter of our Sun and lies approximately 37 light years distant. The orange colour allows astronomers to determine the stars surface temperature a relatively cool 4200 K compared to our Sun’s 5800 K. Arcturus is the brightest star in North of the Celestial Equator. The brightest stars of Boötes form the outline of child’s kite. In Ancient Greece the Heliacal Rising of Arcturus, that is rising just before the Sun, marked the time to begin the harvest of grapes.
Although Boötes is a large constellation there is little of interest within it for users of binoculars and small telescopes except the double star ε (Epsilon) Boötis, “Pulcherrima” given its name by the famous observer 19th century astronomer F G W Struve. Struve noted the contrasting colours of the stars as yellowish orange and bluish green. The description of colours of double stars is always difficult and many observers describe it as orange and green.
Take great care and keep safe. If you would like more information about astronomy please e-mail james.ince1@tiscali.co.uk