GCSE Astronomy Topic 2 - The Lunar Disc

Oblate Spheroid

27.3days

29.5days

Caused by meteorites & comets colliding with the Moon, mostly formed during the early evolution of the Moon. They typically have a sloped wall. It does not have a strong magnetic field & atmosphere like Earth that protects it from impacts.

Some bigger craters have rays that go outwards from the craters in all directions

Darks areas on the Moon also known as ‘seas’ that covers 17% of the Moon’s surface. They appear darker because it contains more iron-rich elements.

Maria formed during a time of heavy bombardment where volcanic activity forced lava to the surface which later turned into basalt

There is less maria on the far side of the Moon

Bright highland areas on the Moon which is normally much more cratered than Maria

Frequently border the Maria which can reach heights of over 5000m which are proportionally higher than the ones on Earth.

Believed to be formed by impacts which released magma under the early lunar surface - the Moon has no tectonic plates

Long depressions on the Moon which are really long & thin. Formed by ancient lava flow, collapsed lava tubes or geological faults. These are also known as ‘Rilles’.

The orbit and rotation period of the Moon are identical - 27.3 days

The same side of the Moon is always facing the Earth

The time the Moon orbits the Earth (27.3days)

The period between the same two phases of the Moon (29.5days)

4cm a year

59%

The equator of the Moon is tilted from its orbital plane, so we can see a little over the polar regions

We can see more of the eastern & western limbs due to the Moon’s elliptical orbit & rotation

When the Moon is nearer the observer’s horizon, we can see more of its surface because we are seeing it from a higher angle

The eastern limb can be seen more at moonrise, whilst the western limb can be more seen at moonset!