Earth’s Motions

Rotation 

Day_Sol_Eq21_RevolvingEarth

Fig. 1 Rotation is the reason for Day and Night

The motion of rotation is the same as spinning. A planet rotates, or spins, on its axis. The axis is an imaginary line that runs from the north pole to the south pole.

Rotation is what creates day and night on a planet. As the planet spins a location will move into the sunlight half and then out of the sunlight.

Looking down on the Earth from the north pole the Earth spins counterclockwise.  This means that we are rotating towards the east and the sun will be first seen on the eastern horizon. 

The sun “rises” in the east and “sets” in the west. The reality is that it is the Earth that is rotating into the sunlight and out of it again.

 

Time Zones

The rotation takes 24 hours and there are 24-one hour times zones around the globe.

24 hr zones

Fig 2.  24 Time Zones

 

Noon is when the location is most directly towards the sun and midnight is when the location is most away from the sun.

 

The diagram to the right (fig 2) shows the sunlight from the right side in yellow, the left side is in the Earth’s shadow creating the night.  Earth rotates counterclockwise and the red dot is approximately the location of Washington DC 

 

 

Revolution 

Revolution is the motion of going around another object, or around a point.  Another term used is to “orbit”.  The planet Earth revolves around the sun.  The moon revolves around the planet Earth.  One revolution around the sun equals one year for a planet. Earth takes 365 ¼ days to make one revolution around the sun. 

The time it takes to make one revolution, one trip around the sun is called the “Orbital Period”.  Orbital for one orbit, and period as a length of time.

Earth’s orbital period = 365 ¼ days = one revolution = one year

EarthOrbit

Fig 3.  Orbit, Tilt, and Seasons

 

Seasons

The earth is tilted 23 ½ ° and the orientation of the tilt (the direction the north pole points) does not change while the earth orbits the sun.

For part of the year the northern hemisphere is pointed (leaning, tilted) towards the sun and receives more direct sunlight making it warmer – and summer. The southern hemisphere is tilted away so the sun’s rays are at an angle and it receives less light/heat making it colder and winter there.

6 months later, the northern hemisphere is now tilted away making it colder and winter.

Revolution and the tilt of the earth give Earth its seasons.

 



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