Why were so many people interested in the study of the movements of the planets? Why is the alignment of astronomical instruments found in Babylon 2.5 degrees out from the present alignment of the Earth? Why did calendars constructed between the middle of the second millennium BCE * and 800 BCE have 360 days and months of thirty days? Why do even earlier calendars have days, months and years of different lengths again?
Velikovsky's answer was that the Earth and Mars had been involved in repeated near collisions with a gigantic comet since our recorded history began. The events described in the Exodus and in Egyptian papyri are a vivid description of an age in chaos—plagues, turmoil and darkness, and the flight of the Hebrews from Egypt toward a "column of fire" in Sinai.
The Earth was momentarily slowed down and its axis slightly altered as the comet passed by. Electrostatic forces caused discharges to arc between the Earth and the comet turning the skies to fire and the forests to flame. The crust was rent, volcanoes erupted, earthquakes rocked and darkness enveloped the world—the time of the Exodus.
All cosmological theories assumed that the planets have evolved in their places for billions of years... Venus was formerly a comet and joined the family of planets within the memory of mankind... We claim that the Earth's orbit changed more than once, and with it the length of the year; that the geographic position of the terrestrial axis and its astronomical direction changed repeatedly and that at a recent date the polar star was in the constellation of the Great Bear.
—Worlds in Collision, p. 361
He predicted Venus would be found to have orbital anomalies in relation to the other planets; Venus has since been found to rotate on its axis in reverse direction to the other planets, and its day is longer than its year. We now know that parts of the atmosphere of Venus rotate in 4 days (with winds of up to 400 km/h) while the planet itself rotates in 243 days. Both these rotations are retrograde.
The comet spiraled past the Earth in an ever-decreasing path around the Sun before taking up its present orbit as the planet Venus. He further cites evidence to show that the Earth interacted with Mars on a number of occasions when writing was better developed than during the Venusian encounters, after Venus flipped Mars out of its orbit.