Cancer
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Forecaster of Ancient Weather and Modern Light Pollution

+ Von Del Chamberlain +

Years ago a good friend put into words something which has been of great importance to me. I have often repeated his words to others, "The starry sky is on the endangered list." At the very time when we know most about the great cosmos, fewer and fewer individual humans see the stars. Reasons for this range from life-styles to light and other atmospheric pollution.

Thus, I want this article to be a challenge to my readers. Each month I have been writing about a constellation of the zodiac, the region of the heavens the Sun, Moon and planets move through. Today, we consider the constellation Cancer, the Crab, the most inconspicuous figure of the zodiac, if not of the entire sky. My challenge is for you to learn to locate and recognize it.

Not a single star of Cancer is brighter than the fourth magnitude. Magnitude is a system of designating the apparent brightness of stars. Derived by Hipparchus about 150 BC, the brightest stars were labeled "first magnitude," and the faintest that could be seen were called "sixth magnitude." Since his time, with the invention of the telescope and other associated equipment, the system has been refined so that the range from first to sixth magnitude represents 100 times in brightness difference. On this modern scale, the brightest star of the night, Sirius in Canis Major, is magnitude -1.5 and astronomers observe objects dimmer than magnitude +25, requiring huge telescopes to discern.

It was Hipparchus who arranged the constellations of the zodiac into the order we now know them. In his time, the Sun reached its apex in the northern hemisphere when it was in the constellation Cancer, the place in the sky and time of year we now refer to as summer solstice. This is the reason the northern boundary of the tropics is referred to as the Tropic of Cancer. At that time the Sun in Cancer would have reached the top of the sky, the zenith, at midday at latitude23 1/2 degrees north, marking the time when the Sun changed directions in its migration north and south. Because of an effect called precession, the summer solstice has slipped out of Cancer into its current location in Gemini.

The idea that this dimmest part of the zodiac represents a crab might have to do with the fact that the Sun turned southward when it reached that part of the heavens. An ancient writer tells us that Chaldeans associated this region with a crab because these creatures walk sideways, then backwards, like the Sun appears to move as it reaches the solstice and turns southward. Possibly related to this, ancient Egyptians called this part of the sky the Scarab, in reference to their concept that an invisible celestial scarab beetle pushed the Sun across the heavens. It is also interesting to note that somehow Cancer, then marking the northern gate of the Sun, became known to Chaldean and Platonist philosophers as the "Gate of Men," through which, they said, souls of people came down from heaven to enter human bodies.

Two old stories about this region come to us from classic times. The Greeks said that Hera (the Roman Juno) sent a crab to attack Hercules as he battled Hydra, the sea monster. It had little effect, for Hercules simply crushed it under foot and went on with the fight. In gratitude, Hera persuaded Zeus to put the crab in the sky, but she, too, apparently cared little for it, marking it with no spectacular stars.

In the other story, the god of wine and intoxication, Dionysus (Roman Bacchus) was on his way to the temple of Zeus when he came to a marsh. Spotting two wild asses, he rode one across the marsh, then sent both into the sky to honor them for their service. This story resulted in two of Cancer's visible stars being called the Aselli, the asses. Both Greeks and Arabs imagined the two stars as asses feeding at the manger represented by a dim cluster of light within Cancer. Ancient ideas always get changed through time. In the 17th century, Cancer was referred to as a Lobster. For some, the dim cluster became the Manger of the infant Jesus with an ass and an ox standing by.

The most notable feature of Cancer is not its few brighter stars, rather it is the cluster of stars that can barely be perceived by the naked eye. Hipparchus referred to it as a "Little Cloud," and Aratus (c. 260 BC) called it a "Little Mist." It was best known as Praesepe. This faint cluster was the basis of an early method of forecasting weather. Indeed, Pliny wrote, "If Praesepe is not visible in a clear sky, it foretells the coming of a violent storm."

It does not take much haziness to obscure the cluster. In fact, in today's world, the problem is to find it at all. In addition to any ancient barometer it might have been to warn of inclement weather, it certainly provides a measure of the conditions we live with all the time. So, here, again, is my challenge. I hope readers will do what is necessary to add this to the list of features they can find and recognize.

This dim constellation has just eight stars that can be distinguished by the naked eye. In addition, the famous cluster, sometimes called the Beehive, can just be made out without optical aid, but none of its individual stars can be seen without a lens. Currently it rises upward in the east as it gets dark after sunset. To find it one must leave the city on a dark, clear night. Locate the constellations of the zodiac identified in my previous articles: then move eastward from Aries through Taurus and into Gemini. Cancer is east of Gemini, midway between the middle of the figure of the Twins and the bright star Regulus, heart of Leo the Lion, the zodiacal constellation I will write about in March. The best advice I can give for finding Cancer is to take binoculars with you and scan the sky east of Gemini for the Beehive cluster. When you find it, I think its beauty through the lenses will impress you, sparkling like a hive of stars. Looking at it, remember that it is one of Utah's official symbols, our Beehive in the sky.

While you are out finding Cancer, I hope you take the time to just look around and enjoy the splendid winter sky, beauty that runs deep in myth, history and science. Let Utah's Beehive in the sky be your personal barometer to gauge feelings about what we see today and changes that have occurred since those old people named the celestial Ram, the Bull, the Twins and the Crab. Think about it. For too many people in our day, the starry sky is, indeed, on the endangered list. Most people will never know the Crab in the sky or the hive of stars it holds, once the weather channel watched by ancient people.

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