Earth's Orbit and Seasons

Earth’s Orbital Motion

The twelve constellations the Sun moves through during the year are called the zodiac constellations.
The path that the Sun travels along throughout the year is called the ecliptic.
The zodiac constellations are found along the ecliptic path.

The ecliptic is the plane of Earth’s path around the Sun.
The plane is tilted at 23.5^\circ to the celestial equator.
Northernmost point: Summer solstice (Sun is highest in the sky).
Southernmost point: Winter solstice (Sun is lowest in the sky).
Points where the path crosses the celestial equator: Vernal and autumnal equinoxes.

A combination of sunlight angle and day length causes the seasons.
Primary reason for seasons is the 23.5^\circ tilt of the Earth’s rotational axis.
This tilt allows the angle at which we receive sunlight to change throughout the year.
Secondary reason is the variation in daylight hours.
- Summertime: More hours of sunlight provide more heat.
- Winter: Fewer hours of sunlight contribute to lower temperatures.
The seasons are NOT due to changes in the distance between Earth and the Sun.
- Earth is actually closer to the Sun during winter (in the Northern Hemisphere).

Summer Solstice
- Longest day of the year.
- Sun is highest in the sky.
- Hot temperatures.
Winter Solstice
- Shortest day of the year.
- Sun is lowest in the sky.
- Cold temperatures.
Vernal and Autumnal Equinoxes
- Occur in between the summer and winter solstices on the calendar.
- Day lengths are in between the lengths for summer and winter solstices.
- 12 hours of daylight everywhere on Earth.