September brings the first crisp, cool nights of early autumn and longer hours of darkness. In short, it is the beginning of the astronomical observing season. Still overhead in the glow of the Milky Way lie the bright Summer Triangle stars Vega, Deneb, and Altair. They are the brightest suns in the constellations Lyra, the Lyre; Cygnus, the Swan; and Aquila, the Eagle, respectively.
From the Summer Triangle the stardust trail of the Milky Way leads eastwards to Cepheus and Cassiopeia, the only married couple among the constellations. In Greek mythology they were King and Queen of Ethiopia, parents of Andromeda.
According to the legend, Cassiopeia made the mistake of bragging she was more lovely than the Nereids, the nymph-daughters of the sea-god Nereus. This brought the wrath of Poseidon, ruling god of the sea, who sent a terrible monster to ravage the lands of King Cepheus. To save his country, Cepheus was forced to offer his daughter Andromeda as a sacrifice to the monster, although she was rescued from the monster’s jaws by Perseus.
You can judge Cassiopeia’s celestial regality for yourself by locating the distinctive “W” her stars always assume. She is above the northeast horizon on September evenings, and from most northern latitudes the constellation is circumpolar – it never sets, due to its proximity to the celestial pole.
One of Cassiopeia’s best sights for binoculars and small telescopes is the open star cluster M52, easily found near the border with Cepheus next to a 5th- magnitude star, 4 Cassiopeiae. M52 is one of the richest open clusters north of the celestial equator, and contains about 100 stars crammed into a relatively small 15′ area. Several individual stars are resolvable in binoculars, but the rest blur into a nebulous mass.
Another cluster visible as a fuzzy patch in binoculars is M103. Telescopes show it to have an elongated shape with a string of four stars immediately to its southeast. While thought to be unrelated to M103, these suns greatly add to its scenic beauty. Look also at the nearby cluster NGC 663, a scattered group of stars of various brightnesses, larger and more prominent in binoculars than M103.
Cepheus, the King, is much less prominent than his Queen. Although faint to the naked eye, Cepheus contains over 20 deep sky objects for binoculars and small telescopes. The constellation is also home to Delta Cephei, one of the most important and most studied stars of all.
Delta Cephei is the prototype of a class of variable stars known simply as Cepheids, which are of particular importance to astronomers – they serve as marker beacons for measuring distances in space. A small telescope shows Delta Cephei as an easy and attractive double, consisting of a 4th-magnitude yellow primary and a 7th- magnitude companion, bluish in color.