Why Are Days Longer & Shorter?

Day lengths vary.

The length of the day changes every day. Days are longer in the summer and shorter in the winter. This has to do with the tilt of the Earth on its axis as it orbits the sun.

Earth's Axis

The Earth's axis is an imaginary line that runs through the Earth between the north pole and south pole. The axis wobbles back and forth throughout the year, moving some parts of the Earth closer to the sun and other parts farther away. This changes the length of the day.

Summer Solstice

The summer solstice is the longest day of the year. It occurs most years on June 21 in the northern hemisphere. The northern hemisphere is tilted toward the sun, providing the longest exposure to sunlight of the year.

Equinox

An equinox is when the days and nights are exactly the same length. This occurs twice in the year, usually on March 21 and Sept. 23. It happens when the Earth's axis is pointed perpendicular to its orbit around the sun.

Winter

The winter solstice is the shortest day of the year. It occurs most years on Dec. 21 in the northern hemisphere. The northern hemisphere is tilted away from the sun, providing the shortest exposure to sunlight of the year.

Opposite Seasons

The season are opposite in the northern and southern hemispheres. When it is summer in one, it is winter in the other.

References

• University of Wisconsin - Milwaukee: The Collaborative Visualization Project: Reasons for the Seasons
• Space.com: The Winter Solstice and Seasonal Fictions