Perseus

From South Dublin Astronomical Society

Perseus

High in the Winter sky, the constellation of Perseus can be seen. It lies between Cassiopeia, Andromeda, Triangulum, Aries, Taurus, Auriga and Camelopardalis.

The name Perseus comes from ancient Greek times. Perseus was the mythological hero who slayed the monster Medusa, who’s sight turned people to stone. Perseus managed to kill Medusa by not looking directly at her, but rather at her reflection in his bronze shield. After killing Medusa, he then rescued the chained woman Andromeda who was being attacked by the sea monster Cetus. All in all, Perseus was a busy fella and consequently his story lives on in the form of a constellation in the sky dedicated to him.

From an astronomy viewpoint, Perseus contains some great deep sky objects, a few decent double stars, the most well known variable star in the night sky and it’s own meteor shower! Not bad eh! In terms of double stars, my personal favourite double star in Perseus is Eta (η) Persei. This is a lovely double star that’s well worth taking a look at. It consists of a pair of yellow and blue stars. It looks like a smaller and fainter version of Albeiro, the double star in Cygnus, which most people would consider to be by far the best double in the entire night sky. Also worth watching is Algol. Algol is probably the most famous of all variable stars visible from these latitudes. It changes it’s brightness over a 10 hour period once every 2.86739 days or 2 days 20 hours 48 minutes and 50 seconds, to you and me! When the cycle starts, the star dims from magnitude 2.1 to 3.4 and back up to 2.1 again over the course of 10 hours. It then remains at magnitude 2.1 for 2.86739 days before the cycle repeats.

Algol is actually two stars, a blue dwarf from which we see most of the light and a fainter yellow star that orbits it. The blue star is much brighter and this is the star we see for most of the time. However, when the yellow star passes in front of the blue star, it blocks more light than it shines, thus Algol appears to dim for a short while. To see a demonstration of this, check out this website: http://www.cosmion.net/software/ebs/

In terms of deep sky objects, Perseus has a few of the best. Most notably is the Double cluster. This is visible to the unaided eye between the top of Perseus and Cassiopeia and a large faint patch of light. The Double Cluster (NGC869 and NGC884, h & χ) consists of a few hundred stars in an open cluster formation. If you have a pair of binoculars, make sure you don’t miss this, as it’s a wonderful target for low magnification viewing.

In the upper right corner of the constellation is M76, the Little Dumbbell. This object is a planetary nebula and is about magnitude 10. You’ll need at least a 3– to 4-inch telescope to see this. In an 8-inch telescope, it appears as a faint dumbbell-shaped patch of light. It is approximately 3,500 light years away. M34 is a cluster of approximately 60 stars and is located a couple of degrees to the upper right of Algol. Binoculars will show this as a small group of faint stars over an area of approximately the size of the full moon.

Near the star Menkib (ξ Persei) lies the [[California nebula]]. To be honest, I mention it here more for completion purposes rather than anything else as it is extremely difficult to see. It is extremely faint and very large — about 3 degrees long. However, when using long exposure photography, it is spectacular. Finally, don’t forget the Perseid meteor shower. This meteor shower occurs between the dates of the 23rd July and 22nd August each year and usually peaks around the 12th and 13th of August. The meteor shower occurs when Earth passes through the trail of debris from Comet Swift-Tuttle. The comet completes one orbit of the Sun every 130 years. As a comet is composed of ice and rock, the ice melts when the comet nears the Sun and a tail forms. Each year, the Earth passes through the dusty remains of Swift- Tuttle’s tail. The dust vaporises in our atmosphere and we see this as a fast trail of light shooting across the night sky. The Perseids are considered the most reliable and rewarding of all the meteor showers.

References

Michael O'Connell TAS, The Constellation Perseus, Arcturus, March April 2006