Seasons and the Angle of Solar Radiation

Rotation: the time it takes a planet to rotate (spin) once on its axis. For Earth = 1 day

Revolution: the time it takes a planet to go once around the Sun. For Earth = 1 year

One year is divided into four seasons; spring, summer, fall, and winter

Spring starts on the vernal equinox ~ March 21Summer starts on the summer solstice ~ June 21Fall starts on the autumnal equinox ~ September 22Winter starts on the winter solstice ~ December 21

Solstice is when the Sun rises or sets as far North or South of the equator as it can (days are longest or shortest)

Equinox is when the Sun crosses the equator, so the days and nights are equal in time

Sun Setting: Nov. 18 Jun. 15

Billions of years ago, before there was life on Earth, a planet about the size of Mars smashed into us. It knocked the Earth over, so instead of rotating around an axis that is straight up and down, we are tilted by 23.5°.

This is what causes the seasons to change, not the distance to the Sun (the Sun is actually CLOSER in WINTER). Because of this tilt, the Earth has longer days in Summer, and more direct sunlight.

45°

On North Pole, as the day passes, what does an observer sees the Sun do?

The Earth’s Orbit

Different constellations are out during different seasons. I can see Orion and Taurus in the south during winter, but in summer I see Scorpius and Sagittarius. This is because the night sky faces different directions.

Polaris, the North Star is directly over the north pole

Because stars are so incredibly far away, Polaris does not appear to move during the night, the Earth just spins underneath it, everything else rises in the east and sets in the west, as the Earth rotates.