This Week’s Sky at a Glance, August 26 – September 2

The constellation Cepheus the King is quite large but it can be difficult to pick out. Around 9:30 pm, look northward for a group of five moderately bright stars in the shape of a house on its side, situated above the W-shape of Cassiopeia the Queen. The peak of the house is only about a fist-width to the right of Polaris, the North Star, and the constellation lies just below a line from Polaris to Deneb at the tail of Cygnus the Swan. A colourful star can be seen in binoculars or a scope just below the base of the house. Herschel’s Garnet Star, a red supergiant, is one of the most luminous stars known and is a thousand times wider than the Sun. If placed in the middle of our solar system it would stretch beyond the orbit of Jupiter.

Another famous star in Cepheus is Delta ( δ) Cephei, which is situated near the bottom left of the house, it being the namesake of the Cepheid variable stars. Such giant stars pulsate with a regular frequency and subsequently dim and brighten consistently over that time. For example, Delta Cephei dims and brightens by a factor of two over about five days. Early in the 20th century, Harvard astronomer Henrietta Swan Leavitt discovered that the intrinsic brightness of a Cepheid variable was proportional to its period and worked out a formula for this relationship. Using the 100-inch telescope on Mount Wilson in the 1920s, Edwin Hubble detected Cepheid variables in what was then called the Andromeda Nebula. Knowing the intrinsic brightness of these stars based on their periods, and how stars dim with distance, he determined the distance to these stars and proved that the nebula was actually a galaxy outside of the Milky Way.

In mythology, Cepheus and Cassiopeia were the rulers of Ethiopia. Poseidon had made a ferocious sea monster to ravage the land as punishment for Cassiopeia’s boasts of their daughter Andromeda’s beauty. To get rid of the monster, they chained Andromeda to the rocks at the seashore as a sacrifice to the monster. She was rescued by Perseus, whose namesake constellation is seen below Cassiopeia.

This Week in the Solar System

Saturday’s sunrise in Moncton is at 6:32 am and sunset will occur at 8:08 pm, giving 13 hours, 36 minutes of daylight (6:38 am and 8:12 pm in Saint John). Next Saturday the Sun will rise at 6:41 am and set at 7:55 pm, giving 13 hours, 14 minutes of daylight (6:47 am and 7:59 pm in Saint John).

The Moon is at first quarter and approaching Saturn on Tuesday, providing a scenic opportunity for stargazing. Setting around 9:30 pm, Jupiter is getting too low in the west for steady viewing in a telescope. Venus makes a pretty binocular companion for M44, the Beehive Cluster, on Thursday and Friday mornings. Mercury is at inferior conjunction this weekend, passing between us and the Sun. It will be at its best morning viewing for the year in September, when it has some close encounters with Mars, Regulus and the Moon.

Questions? Contact Curt Nason using the form below.