Earth’s Motion in Space
Monday, June 15, 2026 11:41 AM
REVOLUTION
- One motion of the Earth in space is its movement around the sun at 66,000
MPH (that would be equivalent to 18.5 miles per second).
○ The path the earth makes around the sun (pulled by its gravity) is from
west to east & covers 600 million miles in one year (which is one
revolution around the sun)
○ Earth revolves once every 365 days, 5 hours, 48 minutes, and 46 seconds,
which adds up to 365 1/4 days
§ Have you ever wondered why we have leap year? Every 4th year, a
whole day would go unaccounted for if we didn't make up for the
extra revolution. So, there is one more day in the month of February
(a 29th day) to account for the extra time it takes each year to revolve
around the sun.
- The path the earth follows as it moves around the sun is called its orbit
○ This path of orbit is an ellipse (not a true circle), which places the earth
closest to the sun in winter ("Perihelion") and farthest from the sun in
summer ("Aphelion”)
○ Perihelion marks the day when the earth is 91,455,000 miles from the
sun, on January 3
○ Aphelion is when the earth is farthest from the sun at 94,555,000 million
miles on July 4
○ You might wonder how it's winter if the earth is closest to the sun during
winter & how it could be summer when the earth is farthest from the
sun. This little difference in distance from the sun (relatively speaking),
has no affect on weather or climate!
Rotation
- Another motion of the earth in space is its rotation, earth spins from west to
east on its N-S axis. The axis is an imaginary diameter line that runs from
pole to pole which the earth spins
- This west-east rotation is counterclockwise looking down from the North
Pole, spinning at a speed of 1,037 MPH at the equator for a complete
rotation once every 24 hours
○ Note: The speed of rotation varies depending on the latitude, as the
circles that cover one rotation get smaller & smaller the more you
approach the poles. So everything on earth's surface rotates once every
24 hours, but different places spin at different speeds
§ For ex., near the poles, the surface barely rotates at all (0mph), but at
the equator, places whiz around at over 1500 ft/sec or 1,037 mph
(about 25,000 miles/day)
- Rotation causes the phenomenon of day and night & fixes the length of days
(24 hours)
- At any moment, half of the earth is illuminated by the sun’s rays & the other
half of the earth lies in darkness
○ The "circle of illumination" is an imaginary circle, created by the
phenomenon of rotation, which divides the earth into a lit (daylight) half
and a dark (night) half
- This west to east rotation in space means the sun, moon & stars "appear" to
rise in the east and set in the west. Earth is actually rotating west to east, so
it only appears they rise in east and set in the west as locations turn into the
sunlight and see it to the east, and rotate away from the sun and look to the
west to see the last glimmers of sunlight
- The sun, moon, and stars do not rise and fall. It is the earth that is moving
toward and away from them.
As mentioned above, the axis upon which earth rotates is an imaginary line
through the poles. It is inclined, or tilted, at 23 ½ degrees away from the
vertical. This tilt has changed and is capable of changing, but very slowly of
many thousands of years. This tilt has a huge effect on the seasons, which is
discussed in the following section.
Monday, June 15, 2026 11:41 AM
REVOLUTION
- One motion of the Earth in space is its movement around the sun at 66,000
MPH (that would be equivalent to 18.5 miles per second).
○ The path the earth makes around the sun (pulled by its gravity) is from
west to east & covers 600 million miles in one year (which is one
revolution around the sun)
○ Earth revolves once every 365 days, 5 hours, 48 minutes, and 46 seconds,
which adds up to 365 1/4 days
§ Have you ever wondered why we have leap year? Every 4th year, a
whole day would go unaccounted for if we didn't make up for the
extra revolution. So, there is one more day in the month of February
(a 29th day) to account for the extra time it takes each year to revolve
around the sun.
- The path the earth follows as it moves around the sun is called its orbit
○ This path of orbit is an ellipse (not a true circle), which places the earth
closest to the sun in winter ("Perihelion") and farthest from the sun in
summer ("Aphelion”)
○ Perihelion marks the day when the earth is 91,455,000 miles from the
sun, on January 3
○ Aphelion is when the earth is farthest from the sun at 94,555,000 million
miles on July 4
○ You might wonder how it's winter if the earth is closest to the sun during
winter & how it could be summer when the earth is farthest from the
sun. This little difference in distance from the sun (relatively speaking),
has no affect on weather or climate!
Rotation
- Another motion of the earth in space is its rotation, earth spins from west to
east on its N-S axis. The axis is an imaginary diameter line that runs from
pole to pole which the earth spins
- This west-east rotation is counterclockwise looking down from the North
Pole, spinning at a speed of 1,037 MPH at the equator for a complete
rotation once every 24 hours
○ Note: The speed of rotation varies depending on the latitude, as the
circles that cover one rotation get smaller & smaller the more you
approach the poles. So everything on earth's surface rotates once every
24 hours, but different places spin at different speeds
§ For ex., near the poles, the surface barely rotates at all (0mph), but at
the equator, places whiz around at over 1500 ft/sec or 1,037 mph
(about 25,000 miles/day)
- Rotation causes the phenomenon of day and night & fixes the length of days
(24 hours)
- At any moment, half of the earth is illuminated by the sun’s rays & the other
half of the earth lies in darkness
○ The "circle of illumination" is an imaginary circle, created by the
phenomenon of rotation, which divides the earth into a lit (daylight) half
and a dark (night) half
- This west to east rotation in space means the sun, moon & stars "appear" to
rise in the east and set in the west. Earth is actually rotating west to east, so
it only appears they rise in east and set in the west as locations turn into the
sunlight and see it to the east, and rotate away from the sun and look to the
west to see the last glimmers of sunlight
- The sun, moon, and stars do not rise and fall. It is the earth that is moving
toward and away from them.
As mentioned above, the axis upon which earth rotates is an imaginary line
through the poles. It is inclined, or tilted, at 23 ½ degrees away from the
vertical. This tilt has changed and is capable of changing, but very slowly of
many thousands of years. This tilt has a huge effect on the seasons, which is
discussed in the following section.
