Diagram caption: The constellation Perseus with its bright stars and surrounding constellations. Perseus is surrounded by (going clockwise from the top): Camelopardalis, Cassiopeia, Andromeda, Triangulum, Aries, Taurus and Auriga. Perseus is home to the notable variable star Algol.

Perseus is a northern constellation and thus the whole constellation is visible at some point in the year throughout the northern hemisphere. The whole constellation is also visible to equatorial regions of the southern hemisphere with parts of the constellation visible to southern temperate regions. Perseus is best viewed in the evenings in the northern hemisphere winter and southern hemisphere summer.

The open clusters NGC 869 and NGC 884 (commonly known as the Double Cluster) lie in Perseus as does the open cluster M34. These are all marked with yellow circles. The brightest star in Perseus, Mirfak (alpha Persei), along with some of the surrounding stars are members of the Alpha Persei open cluster. The planetary nebula M76 also lies in Perseus, it is marked here with a green circle superimposed on a plus sign.

The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dot marking Algol is surrounded by a circle, showing it is a variable star. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. The blue line at the bottom left of the diagram marks the ecliptic. Neither the constellation boundaries, nor the lines joining the stars, nor the ecliptic, appear on the sky.

Diagram credit: Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope. Credit Link

Related glossary terms: Apparent Magnitude , Celestial Coordinates , Constellation , Declination , Ecliptic , Open Cluster , Planetary Nebula , Right Ascension (RA) , Variable Star
Categories: Naked Eye Astronomy

Diagram license: Creative Commons Attribution 4.0 International (CC BY 4.0) Creative Commons Attribution 4.0 International (CC BY 4.0) icons