Earth, Moon, and Sun: Days, Seasons, Phases, and Tides

Days, seasons, moon phases, and tides all come from the motions of three bodies: the Earth, the Moon, and the Sun. These are among the most tested space-science ideas, and each has a clear cause once you picture the motions.

Days and Seasons

A day happens because Earth rotates on its axis once every 24 hours; the side facing the Sun has daytime, the other side has night. Seasons happen because Earth’s axis is tilted as it orbits the Sun over a year. The tilt means different parts of Earth get more direct sunlight at different times — summer where sunlight is direct, winter where it is slanted. A common myth to avoid: seasons are not caused by Earth being closer to or farther from the Sun; they are caused by the tilt.

Moon Phases

The phases of the Moon come from how much of the Moon’s sunlit half we can see as it orbits Earth. The Moon does not make its own light; it reflects sunlight. As it moves around Earth, we see different amounts lit — from a dark new moon to a fully lit full moon and back.

Tides

Tides — the daily rise and fall of the ocean — are caused mainly by the Moon’s gravity pulling on Earth’s water. The side of Earth facing the Moon (and the opposite side) bulges outward, creating high tides, while other areas have low tides. The Sun’s gravity adds to the effect. As Earth rotates, coastlines pass through these bulges, so most places get two high tides a day.

Watch: A Short Video Lesson

Cored Education walks through this skill clearly in a few minutes. It is a helpful companion to the reading above:

A Routine for These Questions

1. Day/night comes from Earth’s rotation.
2. Seasons come from Earth’s tilt, not its distance from the Sun.
3. Moon phases come from how much of its lit half we see as it orbits.
4. Tides come mainly from the Moon’s gravity pulling on the oceans.

Practice

1. What causes day and night?
2. What causes the seasons?
3. Does the Moon make its own light?
4. What causes the phases of the Moon?
5. What mainly causes ocean tides?
6. True or false: seasons are caused by Earth’s distance from the Sun.

Answers

1. Earth’s rotation on its axis.
2. The tilt of Earth’s axis as it orbits the Sun.
3. No — it reflects sunlight.
4. How much of the Moon’s sunlit half we can see.
5. The Moon’s gravity pulling on the oceans.
6. False — the tilt causes seasons.

Where This Fits in Your Science Prep

This builds on the solar system and leads into eclipses and stellar life cycles. See all topics on the Science Topics Hub.