Stockton Astronomical Society
Valley Skies - March 1998 Issue
Constellations:
Cancer
Genitive: Cancri
Abbr: Cnc
Meaning: The Crab
Cancer is one of the twelve Zodiac constellations and is highest in the sky around 10pm on the 1st of March. It is located close to the center of a triangle formed by Procyon in Canis Minor, Pollux in Gemini and Regulus in Leo. Because of it's lack of bright stars or a clear pattern, this method for finding it works best for me.
It has been called a tortoise by the Babylonians, or a scarab by the Egyptians as far back as 4000BC. By 2000BC it was referred to as a crab or related clawed creature by most civilizations. To some Greeks this area of the sky was known as the "Gate of Men" where it was believed that souls passed through coming to earth to enter human bodies. Also, from the Greeks, are the tales of Heracles who fought and killed Hera's pet monster, the Hydra. During or after the battle, Hera sent a giant crab to kill Heracles, but it only managed to bite his heel before the mighty hero was able to crush it. Hera then rewarded the crab for his courage with a place in the sky by the head of Hydra.
Exploring in Cancer
Starting at the southern end, or foot, of the crab is the double star 17 Beta Cancri, called Al Tarf. From this point heading east toward 65 Alpha Cancri there is a triangle formed by 37 Cnc, 36 Cnc and VZ Cnc. VZ Cnc is a pulsating variable that changes about every two hours. Continue on to 65 Alpha Cancri (Acubens), and its 11th magnitude companion star. Just to the west of Acubens is M67 (NGC2682), believed to be one of the oldest open clusters, since its core stars are closer together than the cores of most other open clusters and it contains very few young blue stars. M67 is 2.4 kly away from us and can be seen with binoculars. However, it will take a scope with an aperture larger than 6 inch to distinguish many of the individual stars.
Note: The chart included here provides only a rough guide to the constellation. To follow the detailed description, refer to charts 6 & 12 in Tirion's Sky Atlas 2000 (or equivalent).
Traveling NW from M67 is Tegmine (16Zeta Cancri A, B and C) a triple star system. Zeta A and Zeta B are too close together to be separated by a small scope, so find someone with a light bucket at a star party if you want to see them. The third member, Zeta C is easier to separate being almost 6 arcsec. away from Zeta A & B. This system is getting closer to the sun at a rate of 8 km/s.
Follow the faint stars east from Tegmine to Asellus Australis (47 Delta Cancri) which is an open double. Asellus Australis is also known as the Southern donkey with Asellus Borealis (43 Gamma Cancri) being the Northern donkey, drinking at the "manger".
Northwest of Delta Cancri is the naked eye visible open cluster M44 (NGC2632), aka Praesepe (meaning the "manger") or the Beehive Cluster. It was first considered to be a nebula (cloud) before the invention of the telescope. M44 was one of the first things Galileo studied through his telescope. Near the Center is a triple star system of 7th mag. that forms a small triangle. M44 is approximately 600 ly away and is also believed to be an old cluster.
Cancer also has six galaxies in its boundaries: NGC 2608, 2623, 2524, 2749, 2764 and 2775, all of which are 12th mag. or dimmer except 2775. NGC2775 is mag. 10.3 and it is near the border of Hydra, roughly at the end of a line running from Tegmine through M67. I will try to cover it when I do Hydra.
Clear Skies...Eric
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Lasted Updated: 11/28/2000
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