Cancer Constellation
Cancer constellation
On star charts Cancer is usually outlined only with the stars marked in red.
  • Cancer is visible in both the Northern and Southern hemispheres.
  • In the Northern hemisphere the constellation can be seen from late autumn to spring.
  • In the Southern hemisphere Cancer can be seen in the summer and autumn months, note that it will appear upside down.
  • Most of the stars that make up Cancer are quite faint, as a result it is one of the dimmest constellations.
  • The brightest star in the constellation is Altarf, which is over 500 times more luminous than the sun.
  • In Latin cancer means crab.
  • The Tropic of Cancer is named after the constellation.
  • The Tropic of Cancer is a line of latitude which marks the most northerly point at which the sun can be viewed directly overhead.
  • On this line the sun now falls within the constellation of Taurus at the summer solstice, but in ancient times it was in the constellation of Cancer.
  • Cancer is based on a 3,000 year old Babylonian constellation which was named "The Crayfish".

Cancer Mythology

Cancer mythology
Cancer is associated with the crab and is one of the twelve signs of the zodiac.
The constellation of Cancer is associated with Greek mythology. The myth is based around the character of Hercules, a divine hero and son of Zeus. Throughout his life Hercules was tormented by his step-mother Hera who continually made attempts to kill her stepson, the constant torment eventually drove Hercules insane. In his madness the hero took the life of his six sons, when Hercules recovered from his mental illness he sought to serve penance for his actions.
Hercules was advised to put himself under the control of King Eurystheus who would set him a series of labors. The second of these labors would require Hercules to kill the Hydra, a multi-headed serpent creature which dwelt in swamps around Lake Lerna. Hera watched on in horror as Hercules began slaying the creature, in order to distract him she sent a crab to bite at his ankles, the hero simply crushed the crab under his foot before killing the Hydra. After the battle Hera placed the crab in the sky to honor his service.

Main Stars in the Cancer Constellation
Cancer constellation
The number next to each star is its apparent magnitude, its brightness from our point of view on Earth, the lower the number the brighter the star in the night sky.
Altarf
Also known as Beta Cancri and the brightest star in the constellation, Altarf is an orange giant around 290 light years from Earth, the star is around 50 times larger in diameter than our sun.
Acubens
Also known as Alpha Cancri, Acubens is a white main sequence star with a similar radius to our sun but with twice the mass, it is located around 175 light years from Earth.
Asellus Australis
Also known as Delta Cancri, Asellus Australis is an orange giant star around 180 light years from Earth.
Asellus Borealis
Also known as Gamma Cancri, Asellus Borealis is around 160 light years from Earth and is a white star in the process of becoming a giant.
Iota Cancri
A two star system around 300 light years from Earth, the brightest of the two is a white giant while the other is a white main sequence star.

Finding Cancer - Northern Hemisphere
finding Cancer northern hemisphere
The chart shows the position of Cancer over most of the United States in mid-winter at 8 pm. This chart can also be applied to other areas of the Northern hemisphere such as Canada, the UK and Europe. Cancer rises in the north-east and sets in the north-west, in December the constellation will appear in the eastern night sky around 10 pm and continue westward until around 7 am, from January to February it will first appear from the east as night falls around 6pm before setting around 6 am, and from April to June it will first appear in the south-west around 9pm and dip below the horizon around 1 am.

Finding Cancer - Southern Hemisphere
finding Cancer southern hemisphere
The chart shows the position of Cancer over most of Australia in early autumn at 8 pm. This chart can also be applied to other areas of the Southern hemisphere such as New Zealand, South Africa and South America. As in the Northern hemisphere Cancer rises in the north-east and sets in the north-west, from January to March the constellation will first appear low on the horizon in the north east between 10 pm and midnight and continue westwards until day breaks, from April to May it will appear in a more northerly direction as night falls between 6 and 7 pm and dip below the horizon between 10 pm and 2 am depending on the month.


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