Go out at 9 or 10 p.m. PDT in September and look to the east (the later you look the higher Pegasus will be in the sky). You’ll see a large square of stars, aka the Great Square of Pegasus.
This marks the body of the winged horse Pegasus. To the left (west) are the head and front legs. You see, Pegasus is depicted as flying out of a cloud, so we don’t get to see the entire winged horse. According to Greek myth, Pegasus was born out of the body of the headless Medusa (Perseus had just cut off her head). Pegasus flew off and was eventually captured by the hero Bellerophon.
Pegasus is the seventh largest constellation in our sky. Many of the brightest stars have Arabic names. For example: Markab (Alpha Pegasi), apparent magnitude 2.5 , meaning the saddle of the horse; Scheat (Beta Pegasi), a semi-regular variable, magnitude 2.3 to 2.7, meaning the leg; Algenib (Gamma Pegasi), a Cepheid variable, meaning the flank; Enif (Epsilon Pegasi), meaning the nose. Markab, Scheat and Algenib form the great square.
Oops, but wait! It takes four stars to form a square! The fourth star is actually now known as Alpheratz (Alpha Andromedae), formerly known as Sirrah (Delta Pegasi) when it was part of Pegasus. In 1922, when constellation boundaries were set, Alpheratz\Sirrah was placed in the constellation of Andromeda.
Pegasus contains a Messier object (Messier was a comet hunter who decided to catalogue objects that were not comets), M15. Using binoculars, M15 can be found by using Enif (the nose of Pegasus) as a starting point and scanning 4 degrees to the northwest of Enif. M15 is a globular cluster easily seen in binoculars. It is one of the most densely packed globulars known. It might even have a central black hole.
M15 is notable because it contains a large number of variable stars (112) and pulsars (8 rotating neutron stars). It also contains the first planetary nebula (Pease 1) discovered within a globular cluster (discovered in 1928).
Pegasus is noteworthy for another reason. It contains the first extrasolar planet (51 Pegasi b) found around a sun-like star (51 Pegasi) 50 light years away. This planet is a hot Jupiter that orbits the star in four days. Its surface temperature likely exceeds 1,800 degrees Fahrenheit!
51 Pegasi, at magnitude 5.5, forms a very flat triangle between Alpha (Markab) and Beta Pegasi (Scheat). You’ll need at least binoculars to see it. Another star, HR8799 is close to 51 Pegasi. HR8799 is 129 light years from Earth and also has exoplanets. Three of these planets have been directly imaged in 2008.
There is a fourth planet, found after observations in 2009-2010 that is inside the orbits of the other three but still is 15 times farther from its sun than the Earth is from our Sun.
Resource: HVA club
The Heart of the Valley Astronomers is a group of amateur astronomers dedicated to sharing our passion for the sky with the local community. We meet on the second Tuesday of each month (next: September 10 at 7 p.m.) at the Walnut Community Room, 4950 NW Fair Oaks Drive in Corvallis. Meetings are free and open to everyone. For more information, see www.hvaastronomy.com, or visit us on Facebook.
We also regularly schedule star parties, technical assistance, astronomy classes through Corvallis Parks and Recreation and educational outreach for public and private groups. For more information see www.hvaastronomy.com, or look us up on Facebook.
Question of the Month
This month: When is the Earth closest to the Sun?