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The name comes from the Latin; cancer means crab. The crab in
question is the one sent by Hydra to attack Heracles. It was only a bit
part, but one which secured its immortality.
Heracles tracked the animal down, but the lion had fur which was impervious
to iron or bronze. Thus Heracles' arrows bounced off the animal, and his
sword bent, and his club broke into pieces.
The only thing left was to wrestle the thing, so in a mighty contest Heracles
fought the beast. The lion managed to nip off a finger from our hero, but
eventually Heracles choked the life out of the Nemean Lion. Thus ended the
First Labour.
Since nothing else would cut the lion's pelt, Heracles cleverly used its
own claws to skin the animal, and fashioned the impervious pelt into his own
protective clothing. Thus attired, he set off to accomplish his Second
Labour: to kill the Lernaean Hydra.
Nearby lay the swamps of Lerna, home of the Hydra, an enormous dog-like
monster with nine heads (one of which was immortal), and with breath
that would kill on contact.
With the help of Athene Heracles located the monster's lair and the
ensuing struggle was a standoff: as one head was sliced off, another
appeared in its place. Then at Hydra's bidding, a giant crab emerged from
the swamp and bit into Heracles' foot. Heracles promptly killed the animal
then cut off the Hydra's immortal head, killing it as well. He then
dipped his arrows in the Hydra's gall; the slightest scratch from one of
these arrows would bring instant death to his enemies.
While rather small, Cancer still has a number of fine objects, including
a splendid star cluster and several visual binaries.
Phi Cancri is a binary of two identical white stars (5.5m, 6m):
the PA is 217º and separation is 5.1".
Iota Cancri is a wide binary (4.5, 6.5) with a striking colour contrast:
yellow and blue. PA 307º separation 30.5".
Finally, for the perseverant, there are a number of binary systems visible
in the Beehive Cluster (see below).
Cancer has no outstanding variables, but there are two which might be of
some interest.
These stars are divided into three groups: those with predominantly silicon
spectral lines, those with manganese, and those with chromium-strontium lines.
Kappa Cancri shows a strong manganese line.
R Cancri is a Mira-type variable with period of 361.6 days and a
magnitude change from 6.07 to 11.8. In the year 2000 the maximum should
arrive in the first week of October.
Cancer has two Messier objects, M44 and M67.
This grouping is so large it was well-known in antiquity, when it was
thought to be a nebula, or gaseous region of the sky. The cluster often
served to predict the weather: if not crystal clear inclement weather
might be on the way.
Galileo was the first to study its stars with a telescope. He counted over
forty members, putting to rest the idea of its nebulosity and introducing
the idea of star clusters.
There are over three hundred stars in the Beehive (the Webb Society
Handbook claims 2000). It has been estimated that over a hundred of its
stars are brighter than our Sun, and in fact (as Burnham points out) if
the Sun were a member of this group, it would be a very modest member
indeed, at about 10.9 magnitude.
Being so old, many of its stars have nearly completed their life-cycle,
having passed through the red giant stage and now having "jumped off"
the main sequence and entering another phase. Indeed, this is how the
age of such clusters is determined.
It is assumed that all members of a star cluster evolved out of the
same gas cloud at roughly the same time (give or take a few million years).
These stars spend a given length of time on the main sequence, relative
to their mass. For example, stars equal to one solar mass will spend about
ten billion years on the main sequence. Since the stars of the Beehive
Cluster are rather similar to the sun, its age has therefore been
calculated to be at least 10 billion years.
For a closer appreciation of Cancer, visit the Binocular Section.
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