This Week’s Sky at a Glance, 2019 August 17– 24 ~by Curt Nason
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 and 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 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 period 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 6:20 am and sunset will occur at 8:25 pm, giving 14 hours, 5 minutes of daylight (6:27 am and 8:28 pm in Saint John). Next Saturday the Sun will rise at 6:29 am and set at 8:12 pm, giving 13 hours, 43 minutes of daylight (6:35 am and 8:16 pm in Saint John).
The Moon is at third quarter on Friday, rising before midnight Thursday and setting at 2:25 the following afternoon. Jupiter is at its highest at sunset, followed by Saturn two hours later. Telescope users might see Jupiter’s Red Spot around 10 pm on Wednesday and 11:30 pm on Friday. Mercury rises about an hour before the Sun and is an easy binocular target in twilight. Venus and Mars are on vacation for a while.
There will be public observing at the ball field in St. George on Friday, August 23, with a cloud date of August 24. The annual RASC NB Fundy Stargaze will be held on August 30 and 31 at the Herring Cove campsite in Fundy National Park.
Questions? Contact Curt Nason.