Earth & Space Vocabulary
Use technical vocabulary for Earth's motion and the wider universe: rotation, revolution, axis, tilt, orbit, light year, gravitational force, atmosphere, lunar phases, waxing, waning, solstice, equinox, eclipse, and apply these when explaining day and night, the seasons, and the Moon's phases
What a learner can do afterwards
- Use 'rotation' and 'revolution' correctly to describe Earth's two distinct types of movement and explain what each causes
- Use 'waxing' and 'waning' to describe the Moon's phases and explain what causes them
- Apply 'solstice' and 'equinox' correctly when explaining why seasons exist and why day length varies
1 · Read
Earth is always spinning around an imaginary line through its middle, called its axis. This spin is called rotation. One full rotation takes about 24 hours, which is one day. Rotation is why we get day and night: the side of Earth facing the Sun has daylight, and the side facing away has night.
At the same time, Earth is also traveling all the way around the Sun on a path called an orbit. This trip is called revolution. One full revolution takes about 365 days, which is one year. Rotation is a quick spin, but revolution is a much longer journey.
Earth's axis is not straight up and down. It leans, or tilts. Because of this tilt, some places get more direct sunlight at different times of the year, which causes the seasons. A solstice is the day with the longest or shortest daylight of the year. An equinox is a day when daytime and nighttime are almost exactly equal.
Maya watches the Moon every night for a month. First she sees a thin sliver of light. Each night the lit part grows a little bigger, which astronomers call waxing. After the Moon is fully lit, the lit part starts shrinking each night instead, which is called waning. These changing shapes are the Moon's phases, caused by seeing different amounts of its sunlit side as it orbits Earth.
Two more words are worth knowing. Gravitational force is the pull that keeps Earth orbiting the Sun and keeps our atmosphere, the layer of air around Earth, from drifting off into space. And when the Moon, Earth, and Sun line up just right, we get an eclipse.
Rotation spins Earth to make day and night, revolution carries Earth around the Sun to make a year, and the Moon's waxing and waning come from watching its sunlit side change.
More to read
How to Tell Whether the Moon Is Waxing or Waning: A Guide
The moon takes 27.3 days to orbit Earth, but the full lunar cycle takes 29.5 days. Throughout the cycle, the moon waxes (grows more visible) then wanes (grows less visible). The moon doesn't create its own light; it reflects sunlight. When the moon is between Earth and the Sun, we see the dark new moon. When Earth is between the moon and the Sun, we see the full moon. The phases are: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent. 'Waxing' means the lit part is growing. 'Waning' means it's shrinking.
Key points: Seasons
Earth's axis is tilted. As Earth orbits the Sun, different parts of Earth point toward or away from the Sun. This causes the seasons. When the Northern or Southern Hemisphere points toward the Sun, it's summer there. The Sun's rays are more direct. When a hemisphere points away from the Sun, it's winter. The Sun's rays are less direct. The Northern and Southern Hemispheres always have opposite seasons. Solstices mark the longest and shortest days. Equinoxes mark when day and night are equal.
8.4 Earth in Space
Earth has two main motions. Rotation is spinning on its axis once every 24 hours, causing day and night. Revolution is orbiting the Sun once per year, causing the seasons. The axis is the imaginary line through Earth's center. Tilt is the angle of the axis relative to the orbit (about 23.5 degrees). Orbit is the path Earth follows around the Sun. A light-year is the distance light travels in one year. Gravitational force is the pull between masses. Atmosphere is the layer of gases surrounding a planet. Lunar phases are the changing appearance of the moon. Waxing means growing more visible. Waning means growing less visible. A solstice is the longest or shortest day. An equinox is when day and night are equal. An eclipse is when one body blocks another's light.
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2 · Watch
En anglaisTake it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.