Constellation of the Month: Cancer: The Crab.

by Mark S Deprest
Printed in Reflections: March, 2001.

Cancer, the crab seems to have been put into the sky to help fill in the 12 signs of the Zodiac and to sort of tie these 12 signs to the story of the 12 labors of Hercules.  The Crab played a bit part in the second labor.  Where Hercules is to kill the Hydra, a multi-headed, giant water serpent.  The Hydra lived in the marshes Lerna in Greece.  Now there are a number of different versions to just how Hercules finally managed to overcome the Hydra, which seem to have a rather unique ability to grow two heads back each time our hero would lop off one.  Hercules finally figured out that if he put fire to the wound it would sear and seal it shut, so that new heads could not grow up through the old wound.  The Hydra was also renowned to have an extreme case of halitosis (breath that could kill), possibly caused by all that Greek food and the absence of dental floss.  While the battle raged, Juno sent a large crab to attach Hercules’ flank, possibly the first recorded case of a woman getting one of her friends to pinch the cute guy’s butt.  Hercules quickly disposed of the crab and cut off one its claws which he then used to kill the last remaining head.  Hercules dipped the tips if his arrows into the festering wounds and coated them with the Hydra’s deadly juices, so that even the smallest scratch from one of his arrows would result in death.

Transit at Midnight of Alpha Cancer: February 13th

The constellation is situated from 6 degrees North to 33 degrees North declination and is bordered on the East by Leo at 9 hours and 22 minutes Right Ascension, and to the west by Gemini and Canis Minor at 8 hours Right Ascension.  Most of the stars that make up Cancer are rather faint to the naked eye.  Alpha Cancri; Acubens is a 4.26 magnitude A3 spectral class star.  Beta Cancri; Altarf is a 3.52 mag. K2 spec. star.  Delta Cancri; Asellus Australis is a K0 spectral class star that shines at 3.93 magnitude and Gamma Cancri; Asellus Borealis shines at a meager 4.67 magnitude.  Zeta Cancri; Tegmen is a very nice triple star system where Zeta A is a 4.67 magnitude G0 class star.

Things to Check Out in Cancer:

Multiple Star Systems

Zeta Cancri; STF1196; ADS 6650

• RA (J2000):  08h 12’12.71” declination:  +17d 38’53.3”
• Included in the Astronomical League’s certificate list of 100 double stars.  Included in the Saguaro Astronomy Club’s list of 110 best multiple stars.  Visual binary star.  Included in Michael R. Feltz’s list of the widest visual binaries.
• Orbital elements and diagram available on Richard Dibon-Smith’s website:  (http://www.dibonsmith.com/).
• Component A:  magnitude +5.6 spectral type F8V
• Component B:  magnitude +5.9 spectral type F9V
• Component C:  magnitude +6.0 spectral type G5V
• Separation AB:  0.8” at position angle 83
• Separation AC:  5.9” at position angle 73
• Discovered by Mayer in 1756.  Thought to be a double star until 1781, when Herschel discovered the third component.  The three stars are sometimes said to be yellow, orange and white, although the spectral classes do not really bear this out.  Muirden (1988) adds that the unsplit AB appears golden yellow.
• Distance:  83 light-years
• Projected orbital separation:  15 AU between A and B; 150 AU between AB and C
• Luminosity (Sun =1):  A 3 B 2.1 C 1.7
• Diameter (Sun =1):  A 1.5 B 1.3 C 1.4

Iota Cancri; STF1268; ADS 6988

• RA (J2000):  08h 46’41.83” declination:  +28d 45’36.0”
• Included in the Astronomical League’s certificate list of 100 double stars.  Included in the Saguaro Astronomy Club’s list of 110 best multiple stars.  Components show no relative motion.  Components display common proper motion.  Colorful double star.
• Component A:  magnitude +4.2 spectral type G8III
• Component B:  magnitude +6.6 spectral type A3V
• Separation AB:  30” at position angle 301
• The color contrast is usually described as yellow (or orange) and blue.
• Distance:  300 light-years
• Projected orbital separation:  2750 AU
• Luminosity (Sun =1):  A 145 B 16
• Diameter (Sun =1):  A 20 B 1.6

Phi 2 Cancri; STF1223; ADS 6815

• RA (J2000):  08h 26’ 47.08” declination:  +26d 56’ 07.7”
• Included in the Saguaro Astronomy Club’s list of 110 best multiple stars.  Components display common proper motion.
• Component A:  magnitude +7.0 spectral type F0III
• Component B:  magnitude +7.9 spectral type A3V
• Separation AB:  5” at position angle 217
• First observed by Struve in 1822.  Star A may be a variable.  Described by Muirden (1988) as “a fine white pair.”
• Distance:  250 light-years
• Projected orbital separation:  383 AU
• Luminosity (Sun =1):  A 7.6 B 3.3
• Diameter (Sun =1):  A 1.8 B 0.8

Deep Sky Objects

M44; NGC 2632; Beehive Cluster; Praesepe

• Praesepe is latin meaning crib or manger.
• Right ascension:  08h40’00.0” Declination:  +19d 58’ 59”
• Magnitude 3.1
• Angular diameter:  95’
• Distance:  586.8 light-years.
• Brightest star is 6.0 mag.
• Age 660,000,000 years.  Contains over 300 members.
• Galileo was one of the first to study this open cluster with optical aid and counted forty stars.  Over one hundred of the stars in this cluster are much brighter than our own sun.  In fact if our sun were place in the center of this cluster it would be visible only in a telescope at a magnitude of 10.9.

M67; NGC 2682; open cluster.

• Right ascension:  08h50’24.0” Declination:  +11d 48’ 59”
• Magnitude 6.9
• Angular diameter:  29’
• Distance:  2347 light-years
• Brightest star is 9.0 mag.
• Age 3,900,000,000 years.
• Contains 500 members
• NGC 2682:  remarkable cluster, very bright, very large, extremely rich in stars, little compressed, stars 10th to 15th mag.

NGC 2775; Caldwell 48; spiral galaxy

• J2000 RA:  09h10.3’ dec.:  +07d 02’
• Magnitude 11.4
• Considerably bright, considerably large, round, very suddenly much brighter in middle, resolvable.
• Angular size 5’x 4’ with a Position Angle of 155d.
• Face on view makes this a rather difficult object.
• The supernova 1993Z was found in this galaxy on Sept. 23, 1993 at RA 09h 07.7’ declination +07d 14’ (epoch B1950), magnitude 13.9.

Variable Stars

R Cancri; Mira-type

• Right ascension:  08h16’ 33.8288” Declination:  +11 43’ 34.450”
• Period of 361.6 days.
• Periodic variable with a magnitude range from 6.07 to 11.8.  In 2001 it should reach its maximum at the beginning of October.

Credits

All Images on this page were downloaded from the Sloan Digital Sky Survey.

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