The earth

Understanding the Earth's rotation, orbit, and the motion of the Moon helps us explain the cycles of day and night, seasons, and the phases of the Moon. In this section, we'll explore the Earth's and Moon's movements, as well as introduce the concept of orbital speed.

The earth's rotation and cycle of day and night

The Earth is a planet that rotates on its axis, which is tilted at an angle of approximately 23.5 degrees. The Earth completes one rotation on its axis in approximately 24 hours. This rotation is responsible for the cycle of day and night.

• Daily Motion of the Sun: Due to the Earth's rotation, it appears as if the Sun moves across the sky from east to west. In reality, this apparent motion is caused by the Earth spinning on its axis.

• Day and Night Cycle: When a part of the Earth is facing the Sun, it experiences daytime. As the Earth continues to rotate, that same area will eventually move away from the Sun, entering nighttime.

The earth's orbit and seasons

The Earth orbits the Sun once in approximately 365 days, which is equivalent to one year. The Earth's orbit, combined with the tilt of its axis, is responsible for the changing seasons.

• Seasonal Changes: As the Earth orbits the Sun, the tilt of its axis causes different parts of the Earth to receive varying amounts of sunlight throughout the year.

  • When the Northern Hemisphere is tilted towards the Sun, it experiences summer while the Southern Hemisphere experiences winter.

  • Six months later, the situation is reversed, with the Southern Hemisphere experiencing summer and the Northern Hemisphere experiencing winter.

• The periodic nature of the seasons is therefore a result of the Earth's orbit and its axial tilt.

The moon's orbit and phases