Chapter 3. Earth in Space: Time, Seasons and Location

Earth is an oblate spheroid, slightly flattened at the poles, with an equatorial circumference of about 40,075 km. About 71% of its surface is covered by water [4].

Rotation (once in about 24 hours) causes day and night and the apparent movement of the Sun and stars. Revolution (once around the Sun in about 365.25 days) combined with the axial tilt of about 23.4° produces the seasons [4].

Around the June solstice, the Northern Hemisphere is tilted toward the Sun and has its longest day.

Around the December solstice, the situation reverses.

At the March and September equinoxes, day and night are nearly equal everywhere.

Seasons are caused by tilt, not by changing distance from the Sun.

Time zones. Earth turns 15° of longitude per hour, giving 24 nominal zones. Real zone boundaries follow political borders, and some countries use half-hour or 45-minute offsets. The International Date Line, roughly along 180° longitude, marks where the calendar date changes [1].

Review: If it is noon at 0° longitude, what is the nominal solar time at 90° E?