## What's your sign?

Question 1.0 (1/18/2011):

A song from the famous musical Hair talks about "the dawning of the Age of Aquarius." This refers to the fact that on the date of the vernal equinox the sun is now situated in or at least on the edge of the constellation Aquarius, whereas for about the last 2000 years it has been in the constellation Pisces. This apparent motion of the sun through the constellations of the zodiac is predominantly caused by:

The correct answer was C: The pull of the sun and moon on Earth's equatorial bulge causing the Earth's spin axis to wobble in space.

The sun and the moon pull gravitationally on the equatorial bulge of the Earth trying to bring it in line with, respectively, the ecliptic (the plane of the Earth's orbit) and the plane of the Moon's orbit. Because the Earth is spinning, it does not just come into alignment; instead the force results in a torque on the Earth, causing the spin axis to precess, exactly as a spinning top that is leaning over precesses. This precession of the spin axis is the precession of the equinoxes that causes the equinox to move across the sky, making a complete circuit about every 26,000 years. Since there are 12 constellations along that path, which are each (arbitrarily) assigned an equal fraction of the circuit, it takes about 2,150 years to move from one 'age' to another.

Question courtesy of Glenn Starkman, PhD, professor of physics and astronomy and director of the Institute for the Science of Origins and the Center for Education and Research in Cosmology and Astrophysics. Want more to think about? Read about Starkman's research and watch a video featuring Starkman discussing the science of origins.

Week One Stats

How did you do? 52 people submitted answers for Question 1.0, four contestants selected the correct answer. Average time to correctly answer: 28 seconds. Fastest time? Nine seconds.

Take a shot at the next question, will be posted on Tuesday, April 26, 2011. See other past questions and answers.