Moon, Moon Phases & Eclipses

The Moon

Calendar• The current standard calendar is solar calendar

(Gregorian calendar) – counting days

• The moon phases have a period of 29.5 days, a good measure of time

• Lunar calendars – counting days and months• E.g. Islamic calendar is a lunar calendar• 29.5 * 12 = 354, 11 days less than 365

• Lunisolar calendar – Chinese calendar, Hebrew calendar• Adding leap months, with a circle of 19 years

The Moon’s Orbit around the earth

Moon Phases

When new moon occurs, what is the phase of the earth if you stand on the moon?

Full earth!

The earth always has an opposite phase to the moon.

Eclipses

• When One celestial object casts its shadow on the other one

Solar Eclipses

• Sun – the shadow of the moon on the earth

Total solar eclipse in 1999

A – total eclipseB – annular eclipseC – partial eclipse

Lunar Eclipses

• Moon – the shadow of the earth on the moon

Moon’s orbit

• The orbit period around the earth – 27.3 days• The spin period is exactly the same!• We always see the same side of the moon!

( precisely speaking 59% of the surface during the whole period of the moon revolution. Reason: libration)

• The period of Lunar Phase – 29.5 days• Because of the earth’s revolution in the space

Moon’s orbit

• The orbit plane of the moon is tilted by ~5 degree with respect to the earth’s orbit around the sun, unlike other planets

What’s the moon phase when a solar eclipse occurs?

What’s the moon phase when a lunar eclipse occurs?

New Moon

Full Moon

Why aren’t there solar eclipses and lunar eclipses on EVERYnew moon and full moon?

Two conditions must be satisfied for an eclipse to occur1. The nodes of the moon’s orbit must

be nearly aligned with the Sun and the Earth

2. The phase of the moon must be new or full

Eclipses Cycle

• Every year there are at least two lunar eclipses• Lunar eclipses and solar eclipses always come

in pairs• Lunar eclipses can be seen everywhere on the

earth, but the solar eclipses may only be seen on part of the earth

Near Side Far Side

Moon’s surface

• Maria (sigular mare, ‘sea’ in Latin)– Dark areas and were thought to be

seas– Cover 31% of the near side, but

only 2% of the far side– No water but vast pools of

solidified lava that flowed into basins formed by comets/metors colliding

– Nomenclature • Latin terms describing the weather

and abstract concepts

– Smaller dark regions• Lacus (Lake)• Palus (marsh) • Sinus" (bay)

Maria

Highland

Crater

Moon’s surface

• Highland– Lighter color regions, or

called Terrae– Many are impact basins’

outer rims– In contrast to earth, no

major lunar mountains were formed as a result of tectonic events

– Mountains and mountain ranges

– Different brightness of the highlands and maria is because they are composed of different rock types

Maria

Highland

Crater

Craters

• Formed when asteroids/comets hit the lunar surface

• Half a million craters with diameters larger than 1km

• Crater counting – to estimate the age of the lunar surface

• The largest crater is South Pole-Aitken basin, with 2,240 kms in diameter and 13 kms in depth

• Nomenclature:– Large craters, deceased

famous scientists, artists– Small craters, common first

names• Daedalus, 93 km in diameter• Proposed as a site for a large

radio telescope

The formation of the moon

• Born from the earth - broke off from the earth by centrifugal forces, and left the pacific ocean behind

• Captured by the earth’s gravity• Co-formation with the earth

• Giant impact hypothesis – An impact of a Mars-sized body collide w/ the proto-

Earth and ejected materials to orbit around the earth – the Moon

• http://www.youtube.com/watch?v=UIKmSQqp8wY

Lunar Interior• Most Heavy

materials (Fe, Ni, Etc.) came to earth in the collision

• There is a small iron-rich core

• Mantle and crust is primarily basaltic in composition

Lunar Atmosphere

• *Almost* non-existent– One trillionth the pressure on earth– Trace amounts from multiple sources

• Na/K from “sputtering”

• He-4 from solar wind

• Ar, Ra, & Po from radioactive decay

• No atmosphere has an effect on temperature– Wild variation: 35 K (-238 C) in polar craters– Day side temps up to 396 K (123 C

Explorations of the moon

• Ancient people observed the moon by naked eyes, and wrote poems and essays, and told myths

• Galileo first observed the moon using an telescope

• The only celestial body the human being has orbited and landed– First impact: Luna 2 of Soviet Union in 1959– First far side picture: Luna 3 in 1959– First soft landing: Luna 9 in 1966– First men’s step on the moon: Apollo 11 in 1969

• Several more missions occurred through 1974

• http://www.youtube.com/watch?v=XSLRMdYSA9M