The Baltimore Sun

Pat Koehler in Baltimore asks: "What causes the axial tilt of planet Earth?" Earth spins on an axis tilted 23.4 degrees from the plane of its orbit around the sun. That tilt produces our annual seasons. The initial spin and tilt were the result of impacts as the Earth formed. The drag of solar and lunar gravity have since slowed the spin and altered the tilt some. Tilts vary. Mercury's is 2 degrees; Uranus' is 98

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