« The Lava Connection | Main | Almost Live From the Front Lines »
Even Boring Constellations Have Their Moments
Observing >
In the skies above this month, directly overhead in the evening, is a crustacean called Cancer. It is one of the duller of the constellations, to be sure, but it has a lot of interesting astronomy associated with it.
Like a bad B-movie, Cancer is filled with less-than-brilliant stars. More illustrious are the Crab’s neighbors, the bright Gemini twins to the west, and the backwards question mark of Leo the Lion to its east. All three are part of the Zodiac, a belt of constellations going around the entire sky, the path the sun and planets travel throughout the year.
Only because “Jupiter is in Cancer” is the Crab easy to find this year. Look straight up about 9 o’clock tonight. That really bright “star” is the planet Jupiter. Allow your eyes to adapt to the darkness and, if the skies are crystal clear and the Moon isn’t too bright, you’ll see that Jupiter is caged inside a tiny quadrangle of stars. Those are the stars that make up the body of Cancer.
Have a good time imagining the rest of a crabby body there. It takes a great imagination to see the characters in most all of the 88 constellations, which is one reason why most every people group has its own lore and images about different parts of the heavens.
For example, Germans of the Middle Ages saw in that area a great lobster. People from Tibet pictured a frog here. The ancient Egyptians broke from the water theme and saw their sacred and ever-present beetle, Scarabaeus, in the place of the crab.
With a pair of binoculars you can spot, right next to Jupiter and within the previously mentioned star quad, a bright collection of stars that look like a bevy of busy bees. To no one’s surprise it is called the Beehive Cluster. It is a collection of hundreds of stars about 500 light years away.
Now comes a geographic connection with the old Crab himself. Remember learning in school about the old Tropics of Cancer and Capricorn? Find a globe or a map of the Earth and locate the equator. A special set of lines run parallel to the equator, one to the north and one to the south.
The one running about 23 degrees north of the equator is the line of latitude called the Tropic of Cancer. What is this cryptic name anyway?
When the northern hemisphere is tilted most toward the sun - around June 21, our first day of summer and longest “day” – the sun is directly overhead on the Tropic of Cancer. People living north of this line will never see the sun straight up in the sky; Earth doesn’t tilt that far over.
Now remember that the sun and planets “travel” through the zodiac all year long. (At the moment the sun is in Pisces, on its way to Aries.)
In the old days, in the centuries before Christ, astrology and astronomy were one and the positions of the celestial bodies were being recorded with more and more significance and precision. Then the sun was in Cancer on the summer solstice, the day that it was directly above those living on the Tropic of Cancer! It would go no further northward; instead it would now seem to head back south toward the equator.
Since then the Earth has wobbled out of its ancient position. Nowadays on the first day of summer the sun is visiting the twins in Gemini. But the name “Tropic of Cancer” remains.
Delve deep enough and even a snoozer of a constellation can divulge some interesting gems.
Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.
Posted by Administrator at 2003.04.12 01:39 PM | Comments (0)
