Perseus is one of the oldest constellations, having been cataloged by the Greek astronomer Ptolemy in the second century, and it has more than one attraction for stargazers. It's the center from which the annual Perseid meteor shower, a midsummer spectacle in the Northern Hemisphere, radiates. Also, one of its most famous stars, Algol, is a binary star system that varies noticeably in brightness every 68.75 hours. Perseus looks like a hunter or a dancing man, and it's easy to find by using other well-known star formations as guides. You can also use a star chart.
Using Other Star Formations
Locate the Big Dipper, which is one of the most recognizable star formations in the northern sky. Not a constellation in its own right, the Big Dipper is part of Ursa Major, the Great Bear.
Trace a line between the two stars that form the front of the dipper's pot and extend that line north to Polaris, the pole star. Continue the line past Polaris for about two-thirds of the distance, and it will lead you to the W-shaped constellation Cassiopeia. These two constellations appear to rotate around Polaris as the year progresses.
Locate the third star forming the "W" shape in Cassiopeia, starting from the part of the constellation farthest from Polaris. Draw a line from that star to the second star in the "W" and continue that line for about three times the distance between the two stars to find Mirfak, the brightest star in Perseus.
Locate the Pleiades, which is another easy-to-spot cluster, and imagine a line from that formation to Polaris. Perseus is on this line, so you can use this relationship to verify that you found it.
Using a Star Chart
- Star chart
Perseus is the 24th largest constellation and is visible from latitudes 90 degrees north to 35 degrees south.
You can find star charts online at amateur astronomy sites.
Get a star chart that displays the locations of the stars and constellations from your latitude at the proper time of year. It's best if you use a chart for the proper month, but one that displays the locations for the season is acceptable.
Orient yourself to face north, using a compass, and turn the chart so that north is at the top. East will be on the left side of the map and west on the right, with the center of the chart now corresponding roughly to the sky directly overhead. The east-west orientation is reversed, which may seem counterintuitive. It's because the proper way to view the chart is to hold it over your head as if it were the sky, so when you look down on the map, you are seeing a mirror-image of the sky. If you want to see the direct image of the sky on the map, lay on the ground and hold the map overhead, or you can use a mirror laid on the ground or a table surface. If you have a scanner, you can scan the image and mirror-reverse it using image-processing software, then print it out.
Locate Perseus on the chart, then turn to face the direction indicated and look for Mirfak in the sky. It's the brightest star and easiest to spot. Once you've located it, you can pick out the other stars, including the demon star Algol, by mentally transposing the lines on the chart onto the sky.