Diagram caption: The zodiac constellation Gemini and its surrounding constellations. Starting from the top of the diagram and going clockwise, these are Auriga, Taurus, Lynx, Orion, Monoceros, Canis Minor and Cancer. The brightest stars in Gemini, Castor and Pollux appear in the upper lefthand corner (north-east) of the diagram. In Greek mythology, the stars in this constellation are thought to resemble twins with their arms wrapped around each other, with Castor and Pollux indicating their heads. Gemini lies on 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. The Sun is in Gemini from late June to late July. The other planets of the Solar System can often be found in Gemini.

Gemini lies north of the celestial equator and is visible in all but the antarctic regions of the world. Gemini is most visible in the evenings in the northern hemisphere winter and southern hemisphere summer.

Just to the right of the foot of the Castor twin is an open cluster of stars (labelled as a yellow circle with a dotted line border), Messier 35, also known as the Shoe-Buckle Cluster. This cluster is spread out over an area roughly the size of the full moon. In addition to this cluster of stars, there is a planetary nebula (labelled as a green circle with four radial spikes) – NGC 2392 – near the celestial equator and just to the left of the Pollux twin. Two variable stars (Mekbuda and Propus; labelled as two concentric circles) can be found in the “legs” of each twin, but are so faint that an observer would need dark skies to see them.

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 labelled 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

Diagram translation status: Not yet approved by a reviewer
DOI: https://www.iau.org/public/themes/constellations/
Related glossary terms: 双子座 , 天球坐标 , 星座 , 视星等 , 赤纬 , 赤经（RA） , 金牛座 , 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