This cheat sheet covers how the Moon changes appearance during its monthly cycle and how the Moon and Sun help create ocean tides. Students need these ideas to connect what they see in the sky with predictable patterns on Earth. It also helps explain why phase names, Moon positions, and tide patterns are connected.
The reference is useful for reviewing diagrams, vocabulary, and common cause-and-effect relationships in astronomy.
The Moon’s phase depends on how much of its sunlit half we can see from Earth. A full lunar phase cycle takes about 29.5 days, moving from new moon to full moon and back to new moon. Tides are caused mostly by the Moon’s gravity, with the Sun also adding an important effect.
Spring tides happen when the Sun, Earth, and Moon line up, while neap tides happen when the Sun and Moon pull at right angles.
Key Facts
- The Moon does not make its own light; it reflects sunlight from the Sun.
- A complete cycle of lunar phases takes about 29.5 days from one new moon to the next new moon.
- Waxing means the lit part of the Moon appears to grow larger each night, and waning means it appears to shrink.
- The main phases in order are new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter, and waning crescent.
- A full moon occurs when Earth is between the Sun and Moon, so the Moon’s sunlit side faces Earth.
- A new moon occurs when the Moon is between the Sun and Earth, so the side facing Earth is mostly dark.
- Most coastal places have about two high tides and two low tides each lunar day, which is about 24 hours and 50 minutes.
- Spring tides occur at new moon and full moon, while neap tides occur at first quarter and third quarter.
Vocabulary
- Lunar phase
- A lunar phase is the shape of the sunlit part of the Moon as seen from Earth.
- Waxing
- Waxing means the visible lit part of the Moon is increasing from night to night.
- Waning
- Waning means the visible lit part of the Moon is decreasing from night to night.
- Spring tide
- A spring tide is a tide with the greatest difference between high and low water, caused when the Sun, Earth, and Moon line up.
- Neap tide
- A neap tide is a tide with the smallest difference between high and low water, caused when the Sun and Moon pull at right angles.
- Tidal range
- Tidal range is the height difference between high tide and low tide.
Common Mistakes to Avoid
- Thinking Earth’s shadow causes the regular Moon phases is wrong because phases are caused by our changing view of the Moon’s sunlit half.
- Mixing up waxing and waning is wrong because waxing means the lit portion grows, while waning means the lit portion gets smaller.
- Calling first quarter a half moon can be confusing because first quarter means the Moon is one quarter of the way through its cycle, even though half of its visible disk is lit.
- Assuming spring tides happen only in spring is wrong because spring tides happen during new moon and full moon in every season.
- Forgetting the Sun’s role in tides is wrong because the Moon has the strongest effect, but the Sun’s gravity helps create spring and neap tide patterns.
Practice Questions
- 1 A new moon occurs on March 1. About what date will the next new moon occur if the lunar cycle is about 29.5 days?
- 2 If high tide is at 6:00 a.m. and most places have about two high tides per lunar day, about when is the next high tide?
- 3 Place these phases in order after first quarter: full moon, waxing gibbous, third quarter, waning gibbous.
- 4 Explain why a full moon and a new moon both produce spring tides even though the Moon appears very different from Earth.