The Earth’s Revolution

Revolution – the movement of the Earth around the sun Rotation is one type of motion that the Earth goes through. Another is revolution Revolution – the movement of the Earth around the sun

Evidence of Revolution

One piece of evidence that the earth revolves is the position of the constellations Constellations that are visible in the winter sky are in different positions in the summer or not visible at all.

If the Earth didn’t orbit the sun, no shift would occur Another piece of evidence for revolution is parallax – the apparent shift in position of stars If the Earth didn’t orbit the sun, no shift would occur

The Earth revolves in the same direction as it rotates, counterclockwise as viewed from the North Pole The Earth’s orbit is an ellipse or elongated circle. Because of this the distance between the Earth and the sun changes throughout the year

Aphelion -- the point on its orbit when the Earth is farthest Aphelion -- the point on its orbit when the Earth is farthest from the sun Perihelion -- the point on its orbit when the Earth is closest to the sun

The Earth makes one revolution every 365.24 days (one year)

Effects of Revolution and Tilt

At almost any given time, one hemisphere is tilted toward the sun Effects of the Earth’s revolution and tilt include seasons and variations in night and day At almost any given time, one hemisphere is tilted toward the sun

This tilting is what gives us the four seasons of the year - spring, summer, autumn (fall) and winter. Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter and also because the days are much longer than the nights during the summer.

Sometimes the northern half of the Earth is pointing towards the Sun, and sometimes it is pointing away. These points in the Earth's orbit are called solstices. The summer solstice (around June 21st) marks the point at which the north pole of the Earth is tilted at its maximum towards the Sun The first day of winter (around December 21) for the northern hemisphere is called the winter solstice.

On the first day of summer (June 21), the daylight period is the longest of the year. On the first day of winter (December 21), the daylight period is the shortest

There are also 2 days each year, midway between the solstices when neither hemisphere tilts towards the sun These days are known as equinoxes – daylight and nighttime have equal length

The vernal equinox occurs on March 21 marking the first day of spring The autumnal equinox (September 22) marks the first day of fall