Distinctive Cassiopeia points way to other constellations

On evenings in early October, you can find the constellation Cassiopeia high in the northeast. Cassiopeia is not only an attractive and distinctive constellation but, like the Big Dipper, can serve as a useful pointer to other constellations. Also like the Big Dipper, Cassiopeia is circumpolar at our latitude, meaning that it appears to perpetually circle the north celestial pole, never dipping below the horizon.

Cassiopeia consists of five medium-bright stars that form a "W" or "M" depending on the season and viewing angle. During autumn, Cassiopeia appears as a "W" with the left (northern) side of the letter forming a slightly open angle. To locate Cassiopeia, face northeast and look high in the sky. You can't miss the distinctive "W" shape that is 10 degrees long, nearly as long as the Big Dipper's handle.

To use Cassiopeia's stars as pointers, number them from 1 to 5 starting at the left (northern end). Follow the line from star 3 through star 4 south for 20 degrees to find another constellation that rides high on autumn evenings, Pegasus the Winged Horse.

Pegasus is depicted as flying upside down, head stretched to the west. From urban locations the only stars of this constellation easily visible to the naked eye are the four stars that make up the horse's torso, known as the Great Square of Pegasus. These stars are not as bright as those of Cassiopeia, but are relatively easy to spot because they outline a large square that appears to be completely starless. Each side of the Great Square of Pegasus extends a little over 10 degrees (a fist width at arm's length).

Bright Venus can be found low in the southwest during evening twilight. As the month progresses, Venus gets higher and stays up longer after the sun.

During the last week of the month, Venus passes near the reddish first-magnitude star Antares. On Oct. 29 and 30, a crescent moon joins Venus and Antares to make an attractive grouping.

During early October, Saturn and Jupiter rise in the east-northeast by around 10 p.m. By month's end they rise soon after dark and are visible all night. Saturn rises first and looks like a bright yellow star. Jupiter rises a short while later and is unmistakable because, except for the moon, it is by far the brightest object in the late night sky. As the planets move across the sky, they are separated by only 10 degrees (a fist width at arm's length) with Jupiter to the lower left of Saturn.

Saturn and Jupiter are in the constellation Taurus all month, surrounded by a glorious retinue of bright stars. You will find Saturn below the Pleiades and Jupiter above the bright reddish-orange star Aldebaran. On Oct. 15 a gibbous moon shines close to Saturn and the Pleiades, and on Oct 16. the moon is close to Jupiter and Aldeberan.

Ronald Leamon is vice president-publicity on the Seattle Astronomical Society's board of directors.