Notes Seasons

Think About… What time is it in London right now? What season is it in Australia right now? What causes these differences?

Day and Night Earth’s gravity pulls all objects on Earth toward the center of the Earth. This is what gives us our sense of “up” and “down.”

Day and Night As Earth turns, so do you. Even when you are sitting still, you are moving…

Day and Night Earth rotates at a speed of about 1000 mph.

Day and Night Earth orbits the Sun at a speed of 66,000 mph.

Day and Night Our Solar System is orbiting the center of the Milky Way Galaxy at a speed of about 483,000 mph.

Day and Night The directions North, South, East, and West are based on the way the planet rotates. Axis of rotation- an imaginary line running through the center of the Earth.

Day and Night The ends of the axis of rotation are called the North and South poles. Earth’s otates from West to East.

Day and Night To remember this, extend your right thumb and pretend its tip is the North Pole. Earth rotates in the direction your other fingers are curving.

Day and Night At any given time, about half of Earth is in sunlight and half is dark.

Day and Night When a location is in the sunlit half, it is daytime. When it is in the dark half, it is nighttime.

Day and Night Earth fully rotates in 24 hours, which is why our days are 24 hours long.

Seasons A year is the length of time it takes Earth to complete one revolution around the Sun. Revolution- the motion of one object around another.

Seasons Earth’s axis is tilted at a 23.5 degree angle from the plane it orbits in.

Seasons Earth’s orbit is not a perfect circle. In January, Earth is 5 million km closer to the Sun than it is in July. This has little to no effect on the temperature of Earth.

Seasonal Patterns Seasons- patterns of temperature changes and other weather trends over the course of a year.

Seasonal Patterns Seasonal temperature changes occur because the amount of sunlight at a location changes during the year. The amount of sunlight changes due to the tilt of Earth’s axis.

Seasonal Patterns

Seasonal Patterns Equinox- when sunlight shines equally on the Northern and Southern hemispheres.

Seasonal Patterns Solstice- when sunlight is at a maximum in one hemisphere and a minimum in the other hemisphere.

Seasonal Patterns 1. September Equinox- (Autumnal Equinox) Sunlight shines equally on both hemispheres. Marks the beginning of Autumn in the Northern hemisphere.

Seasonal Patterns 2. December Solstice (Winter Solstice) The North pole seems to lean away from the Sun, due to the tilt of its axis. Beginning of Winter in the Northern hemisphere

Seasonal Patterns 3. March Equinox (Spring or Vernal Equinox) Both hemispheres are equally lit Beginning of Spring in the Northern hemisphere

Seasonal Patterns 4. June Solstice (Summer Solstice) The North pole seems to lean towards the Sun. Beginning of summer in the northern hemisphere

Sunlight You may have noticed that sunlight seems warmer at different times of day. Near sunrise and sunset, sunlight feels barely warm. At noon, sunlight seems to be much hotter. This has to do with the angle it is striking Earth.

Sunlight When the sun is high in the sky (around noon), sunlight strikes the ground at close to a right angle.

Sunlight When the sun is low in the sky, it strikes the ground at an angle, so it is less concentrated, and more spread out.

Lengths of Days Seasonal temperatures depend on the amount of daylight.

Length of Days The farther from the equator, the more extreme the changes in day length. At the North and South pole, the sun rises and sets every 6 months because it is either pointed toward the Sun (in total sunlight) or away from the Sun (in total darkness)