solstice.jpgWhat on Earth Are

Days, Seasons, and Years?

Introduction
When graduates from prestigious colleges like Harvard are asked the reason for the seasons, many answer incorrectly. As 8th graders, you apparently know more than many college graduates about this topic! Days, seasons, and years are explained by the rotation, revolution, and tilt of the Earth. Four questions relating to this topic and responses to them are listed below.

How long is a day on Earth and what exactly is a “day”?
A day on Earth is 24 hours. It is the time it takes the Earth or any planet/moon to make one complete rotation in its orbit. The length of daytime and nighttime can vary depending on how the Earth is tilted. In our summer daytime is longer and in our winter nighttime is longer.

How long is a year on Earth and just what is a “year”?
A year on Earth is 365.25 days. It is the time it take the Earth (or any other planet/moon) to make one complete orbit or revolution around the sun. Earth’s orbit around the sun is not exactly a circle, it is actually an ellipse.

Why do we have seasons?
We have seasons depending on how the Earth tilts relative to the sun. How direct the rays of sunlight are at a point on Earth determines the temperature/season. During the Spring and Autumn the Earth doesn’t tilt toward or away from the sun. During the winter the northern hemisphere tilts away from the sun and gets less direct sunlight, making it cooler (even though we are closer to the sun during our winter). During the summer the northern hemisphere tilts towards the sun and receives more direct sunlight.

What are the four important days in Earth’s revolution and what is true about them?
June 21st-
-Summer Solstice
-First day of summer in the N. hemisphere
-First day of winter in the S. hemisphere
-Longest amount of daytime in the N. hemisphereseasons_lg.gif
-Longest amount of nighttime in the S. hemisphere
-The sun is over the Tropic of Cancer
-24 hours of daytime above Arctic Circle
-24 hours of nighttime below Antarctic Circle

September 22nd-
-Fall/Autumnal Equinox
-First day of fall/autumn in the N. hemisphere
-First day of spring in the S. hemisphere
-Equal amount of daytime and nighttime in each hemisphere
-The Sun is directly over the equator

December 21st-
-Winter Solstice
-First day of winter in the N. hemisphere
-First day of summer in the S. hemisphere
-Longest amount of nighttime in the N. hemisphere
-Longest amount of daytime in the S. hemisphere
-Sun over the Tropic of Capricorn
-24 hours of nighttime above the Arctic Circle
-24 hours of daytime below the Antarctic Circle


March 21st-
-Spring Equinox
-First day of spring in the N. hemisphere
-First day of fall/autumn in the S. hemisphere
-Equal amount of daytime and nighttime in each hemisphere.
-Sun is directly over the equator