Almost anywhere on the planet Earth you will experience day and night. The Earth orbits the Sun along with the 8 other planets in our solar system. It takes the Earth approximately 365 days to complete a full orbit around the sun. The Earth does not sit straight up and down on its axis in space with the North Pole facing directly up and the South Pole facing directly down, but in fact sits on a tilt of approximately 23.5°. At different points in the Earth’s orbit this tilt causes certain parts of the Earth to be closer or further away from the sun and this is what causes the seasons to occur. When each hemisphere is closer to the sun it is spring and summer and when it is further away it is the seasons of fall and winter. It takes approximately 24 hours for the Earth to complete one full rotation or turn on its own axis. This is how we determine the length of our days. It is also what causes day and night.
The cause of day and night
Day and night occur because the Earth rotates on its own axis. During the course of 24 hours the Earth completes a full rotation. When it is day the part of the Earth experiencing sunlight is facing the sun. When it is night the part of the Earth experiencing darkness is facing away from the sun. When it is day on one side of the Earth it is night on the other side. The tilt of the Earth also means that some parts of the Earth experience longer days or nights in different seasons. The countries near the North Pole have very long nights during the winter months and may only experience two or three hours of daylight in a day. However, in the summer they have very long days and may only get a few hours of darkness a day. The countries close to the center of the Earth or along the equator experience days that are a standard length. This is because their exposure to the sun doesn’t change significantly with the seasons.
The following animation shows how the rotation of the Earth causes day and night: