Sun in Cancer

StarDate: August 2, 2009

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If it's your birthday today, you might call yourself a "Leo." But you're in for a little birthday surprise. The Sun isn't in Leo. Instead, it's cruising through the middle of Cancer, the crab.

That illustrates the difference between the astrological and astronomical constellations.

The zodiac was drawn thousands of years ago. It's the string of constellations that the Sun passes through during Earth's year-long orbit. Each constellation was defined as having equal width, so the Sun spent a month within each constellation's borders.

And at the time, those constellations did roughly correspond to the Sun's position during the year.

But Earth wobbles on its axis like a spinning top. So over time, the north pole aims at different points on the sky. As a result, the Sun appears against different constellations as the years roll by.

In 1930, astronomers adopted formal boundaries for the constellations. The constellations form varying sizes and shapes. So the Sun spends varying amounts of time passing through the 13 constellations along its path.

And yes, the number 13 is correct. In addition to the 12 classical constellations of the zodiac, the Sun also passes through Ophiuchus, the serpent bearer. In fact, it spends more time in Ophiuchus than in the adjoining constellation Scorpius.

So when it comes to the zodiac, keep in mind that there's a big difference between the science of astronomy and the pseudoscience of astrology.

Script by Damond Benningfield, Copyright 2009

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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