Term 1 Astronomy Notes: The Moon

Practice flashcards covering general facts about the Moon, its phases, orbital dynamics, and eclipse phenomena.

What is the distance at which the Moon orbits around the Earth?

The Moon orbits the Earth at a distance of $384,399\,km$ ($238,854$ miles).

What causes the Earth's oceans to redistribute and bulge in certain areas?

The gravitational attraction of the Moon pulling more on the parts of the Earth that are closest to it.

What is the mass of the Moon relative to the Earth?

The Moon has a mass of $7.342 \times 10^{22}\,kg$, which is $1/81$ the mass of the Earth.

What is the diameter of the Moon?

$3,474\,km$ ($2,159$ mi), which is roughly one-quarter of Earth's diameter.

What are 'maria' on the Moon's surface?

Dark blotches of lava plains created approximately $4$ billion years ago by giant impacts and lunar volcanism.

Why does the same side of the Moon always face the Earth?

The Earth and the Moon are tidally locked, meaning Earth's gravity slowed the Moon's rotation so that its rotation and orbit are synchronized.

How long is the orbital period of the Moon?

$27.3$ days.

What are the two parts of a Moon phase name?

One part describes the shape of the lit part (e.g., crescent) and the other part tells when it occurs in the cycle (waxing or waning).

What is the definition of a 'Crescent' moon phase?

When the moon is less than half lit.

What is the definition of a 'Gibbous' moon phase?

When the moon is more than half lit.

How is 'waxing' described in the lunar cycle?

The moon is increasing in brightness (from new to full) and the lit part is always on the right.

How is 'waning' described in the lunar cycle?

The moon is decreasing in brightness (from full to new) and the lit part is always on the left.

What physical relationship causes the phases of the moon?

Half of the Moon is always illuminated by the Sun, but as the Moon orbits Earth, the part of that illuminated half we see from Earth changes.

What causes a solar eclipse?

A solar eclipse happens when the Moon passes between the Earth and the Sun, casting a shadow on Earth that blocks the Sun's light.

During which moon phase does a solar eclipse occur?

A solar eclipse occurs only during a new moon.

What causes a lunar eclipse?

A lunar eclipse occurs when the Earth passes between the Sun and the Moon, blocking sunlight from reaching the Moon.

During which moon phase does a lunar eclipse occur?

A lunar eclipse occurs only during a full moon.

Why is it difficult for eclipses to happen frequently?

The Moon's orbit is tilted $5$ degrees off from Earth's orbit, making it hard for the Earth, Moon, and Sun to line up perfectly.

What is a supermoon?

A supermoon happens when a full moon lines up with the point where the moon is closest to Earth in its orbit.

How much bigger and brighter can a supermoon appear compared to a normal full moon?

It can look up to $14\%$ bigger and $30\%$ brighter.