Diagram caption: The constellation Cetus along with its bright stars and surrounding constellations. Cetus is surrounded by (going clockwise from the top): Pisces, Aquarius, Sculptor, Fornax, Eridanus, Taurus and Aries. Cetus lies just south of the ecliptic (shown here as a blue line), this is the path the Sun appears to take across the sky over the course of a year. While the Sun does not pass through Cetus, the other planets of the solar system and the Moon can sometimes be found in Cetus. The star Omicron Ceti or Mira is a famous variable star. This red giant varies in brightness by a factor of 600 over the course of its eleven month period.

Cetus spans the celestial equator, thus some part of the constellation is visible from all the the Earth at some point in the year. The full constellation is visible from equatorial and temperate regions of both hemispheres. Cetus is most visible in the evenings in the northern hemisphere late autumn and the southern hemisphere late spring.

The barred spiral galaxy M77 lies in Cetus as does the spiral galaxy NGC 247 and the dwarf irregular galaxy IC 1613. All three are marked here with red ellipses.

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. Mira is marked with an open circle as it is a variable star not always visible to the naked eye. 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 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. Neither the constellation boundaries, nor the line marking the ecliptic, nor the lines joining the stars appear on the sky.

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

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Related glossary terms: 变星 , 天球坐标 , 星座 , 视星等 , 赤纬 , 赤经（RA） , 黄道 , 黄道十二宫
Categories: Naked Eye Astronomy

Diagram license: Creative Commons 署名 4.0 国际 (CC BY 4.0) Creative Commons 署名 4.0 国际 (CC BY 4.0) icons