We start this article continuing our trip along the Ecliptic, and finish
by travelling across thousands of years.
I've included the Big Dipper, the best-known part of Ursa Major, the Big
Bear, in this month's star map so you can stay oriented. This month's
main constellation, Leo the Lion, is easily found in April - it's a bit
south of the zenith, that point that is straight overhead. Look for the
bright stars Regulus and Denebola, and the distinctive curve of the four
brighter stars of the shoulder and head. Cancer, the Crab, is dim and
hard to find unless you're someplace pretty dark. In suburban areas it
looks like a starless patch between Gemini and Leo. There are two other
really dim constellations on the map - Leo Minor (below Ursa major) and
Leo and Cancer are on the ecliptic, so keep an eye out for planets.
Leo represents the Nemean Lion, killed by Hercules as one of the twelve
tasks set by jealous Hera. After that, Hercules wore the lion's skin as
a cape. You meet Hercules in another article.
Cancer contains the beautiful star cluster M44, called the Beehive. If
it's dark enough where you are, you can see this with just your eyes.
Binoculars or a telescope at low power will show M44 as a beehive of stellar
Faint as it is, geography, time and gravity all meet in Cancer. The Tropic
of Cancer is named for this little constellation. That imaginary line
marks the farthest north the Sun can travel, where the Sun is straight
overhead on the Summer Solstice, the longest day in our northern year.
Thousands of years ago the Sun was in Cancer on the day of the Summer
Solstice. Now Summer's first day finds the Sun in Gemini, on Castor's
big toe, well west of Cancer. You can check it out on your astronomy software
- go to noon on June 21, in this year, and find the Sun. Now switch the
AD to BC. The sun will pop over to Cancer. Two thousand years earlier,
the sun was in Leo when Summer began; 2000 years from now, it will mark
the beginning of Summer in Taurus..
That our seasons drift through the constellations is interesting now,
but when planting and harvesting and religious festivals were foretold
by the stars, it began to cause considerable social disruption. Calendars
had to be rewritten and festivals had to be rescheduled. The leap year
had to be invented, too. All this because Earth spins like any toy top,
with a little wobble induced by gravity. Over the years, that little wobble
adds up to the westward drift of the seasons. The Sun moves through the
ecliptic a constellation per month; the seasons drift more slowly, taking
2000 years for each constellation. We don't notice the seasonal drift
now, since we have clocks, accurate calendars, and an understanding of