What is Gravity?
Gravity is the force of attraction between two objects. The mass and distance affects the force of gravity. For example, if the mass is greater and the distance is closer, the force of gravity is higher.
What is Inertia ?
Inertia is the tendency of an object to continue moving in a straight line. For example, when you are in a moving car, and the car stops suddenly, you may lean forward as if you were pushed. This is called inertia.
Together, gravity and inertia work together to keep Earth in its orbit. (Go to my “More about Astronomy” post for more information about orbit)
Seasons are caused because of the 23 degree tilt on the Earth’s axis. If on one side of the Earth it is summer, the other side is winter.
If the axis is tilting towards the sun, it is summer. If it is tilting away from the sun, it is winter.
Another thing to remember is that if it is winter in the northern hemisphere, it is summer in the southern hemisphere. If it is summer in the northern hemisphere, it is winter in the northern hemisphere. This only applies to the hemispheres of the same side of the globe.
What Causes Day and Night?
Rotation is when a planet spins on it’s axis. It takes 24 hours for Earth to make a full rotation. This is called a day. At any point on Earth’s rotation, 1/2 side of the Earth faces the sun. For this half, it is day. For the half facing away from the sun, it is night. However, day and night are not the same time length. Day is longer than night. This is because of the tilt of the Earth’s axis.