Cancer is one of the zodiac's twelve constellations, and it is in the northern hemisphere. Its name comes from the Latin word for crab, and it is frequently shown as one. Cancer is a medium-sized constellation with a 506-square-degree area and weak stars, the brightest of which is Beta Cancri, which has an apparent brightness of 3.5. It has two known planets, one of which is 55 Cancri, which has five: one super-earth and four gas giants, one of which is in the habitable zone and hence has predicted temperatures like Earth. Praesepe (Messier 44), one of the nearest open clusters to Earth and a popular amateur target, is at the (angular) core of this section of our celestial sphere.
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Characteristics
Cancer is a medium-sized constellation that is bordered to the west by Gemini, to the north by Lynx, to the northeast by Leo Minor, to the east by Leo, to the south by Hydra, and to the southwest by Canis Minor. The International Astronomical Union established the three-letter abbreviation "Cnc" for the constellation in 1922. (Russell 1922) The official constellation borders are determined by a polygon with three main and seven western edgework forming sides, as defined by Belgian astronomer Eugène Delporte in 1930. "Cnc" is the abbreviation for "computer numerical control." The official constellation borders are determined by a polygon with three main and seven western edgework forming sides, as defined by Belgian astronomer Eugène Delporte in 1930. The right ascension coordinates of these borders are between 07h 55m 19.7973s and 09h 22m 35.0364s in the equatorial coordinate system, while the declination coordinates are between 33.1415138° and 6.4700689°. It is the 31st largest constellation in the sky, covering 506 square degrees or 0.921 percent of the sky. It is most visible at 9 p.m. during March and may be viewed at latitudes between +90° and -60°. The bright constellations of Leo, Gemini, and Canis Minor border Cancer. Cancer is invisible to the naked eye under metropolitan skies.
Cancer is a medium-sized constellation that is bordered to the west by Gemini, to the north by Lynx, to the northeast by Leo Minor, to the east by Leo, to the south by Hydra, and to the southwest by Canis Minor. The International Astronomical Union established the three-letter abbreviation "Cnc" for the constellation in 1922. (Russell 1922) The official constellation borders are determined by a polygon with three main and seven western edgework forming sides, as defined by Belgian astronomer Eugène Delporte in 1930. "Cnc" is the abbreviation for "computer numerical control." The official constellation borders are determined by a polygon with three main and seven western edgework forming sides, as defined by Belgian astronomer Eugène Delporte in 1930. The right ascension coordinates of these borders are between 07h 55m 19.7973s and 09h 22m 35.0364s in the equatorial coordinate system, while the declination coordinates are between 33.1415138° and 6.4700689°. It is the 31st largest constellation in the sky, covering 506 square degrees or 0.921 percent of the sky. It is most visible at 9 p.m. during March and may be viewed at latitudes between +90° and -60°. The bright constellations of Leo, Gemini, and Canis Minor border Cancer. Cancer is invisible to the naked eye under metropolitan skies.
Mythology
Claudius Ptolemy originally recorded cancer in Almagest in the 2nd century AD, under the Greek term Καρκίνος (Karkinos). This paragraph was asserted by Richard Hinckley Allen in the late 1890s, with no supporting evidence: "Cancer is claimed to have been the home of the Akkadian Sun of the South, possibly due to its geographical location. In ancient times, it was related to the winter solstice; nevertheless, it was later associated with the fourth month Duzu. our June–July, and was dubbed the Northern Gate of Sun" Cancer was once known as the "Dark Sign," since it had few stars, and its brightest stars were barely 4th magnitude. It was also quaintly characterised as black and without eyes. In Paradiso, Dante alluded to this faintness and its climax at midnight (therefore visibility all night) in a Northern Hemisphere winter month: Then a light shone among them so that if Cancer possessed one of these crystals, Winter would only have a month of one day. In ancient times, Cancer was the backdrop to the Sun's most northerly position in the sky (the summer solstice), or the earth's sun-facing side was maximally tilted towards the south from a physical perspective. Due to the precession of the equinoxes, this position now occurs in Taurus around June 21. This is also the period when the Sun is directly above at 23°N, the Tropic of Cancer's exact parallel. (Ridpath & Tirion 2017) In 1563, tight conjunction of Jupiter and Saturn occurred in Cancer, not far from Praesepe, which was witnessed by Tycho Brahe and caused him to notice the inaccuracy of existing ephemerides and to initiate his own programme of astronomical measurements. Cancer is associated with the crab that appeared during Heracles' battle with the many-headed Hydra in Greek mythology. After the crab bit him in the foot, Hercules slew it. After that, Hera, Heracles' archenemy, placed the crab among the stars. |
Illustrations
Cancer's modern symbol is a crab's pincers, although it has also been symbolised by a variety of creatures, most of which live in the water and always have an exoskeleton. Scarabaeus (Scarab), the sacred emblem of immortality, was documented in Egyptian archives from around 2000 BC. MUL.AL.LUL was the Babylonian name for the constellation, which can allude to both a crab and a snapping turtle. The figure of a turtle or tortoise appears frequently on border stones, and it is thought that this represents Cancer because no traditional crab has yet been identified on any of these monuments. There appears to be a significant link between the Babylonian constellation and conceptions of death and a path to the underworld, which could be the source of later Greek stories involving Hercules and the Hydra. (White 2008) An illustrated astronomical text from the 12th century depicts it as a water insect. In Flowers of Abu Ma'shar, Albumasar mentions this sign. Cancer is depicted as a big crayfish in a 1488 Latin translation, which is also the name of the constellation in most Germanic languages. It was characterised as a lobster by Jakob Bartsch and Stanislaus Lubienitzki in the 17th century. |
Deepsky objects
M44 – Open cluster – Beehive Cluster
M67 – dense open cluster
Main stars - 5
Bayer stars - 76
Stars with planets - 10
Stars brighter than magnitude 3.0 - 0
Stars within 32ly - 2
Bordering
constellations
- Lynx
- Gemini
- Canis Minor
- Hydra
- Leo
- Leo Minor
Meteor showers
- Delta Cancrids mid-December to mid-February with the main shower between 1st - 24th of January
M44 – Open cluster – Beehive Cluster
M67 – dense open cluster
Main stars - 5
Bayer stars - 76
Stars with planets - 10
Stars brighter than magnitude 3.0 - 0
Stars within 32ly - 2
Bordering
constellations
- Lynx
- Gemini
- Canis Minor
- Hydra
- Leo
- Leo Minor
Meteor showers
- Delta Cancrids mid-December to mid-February with the main shower between 1st - 24th of January