Observing the Phases of the Moon

Moon Orbit

• Moon orbits Earth every 27.3 days• As it revolves it also rotates on its axis• Therefore, the same side of the Moon faces

Earth at all times

The Earth, Moon & Sun

Sun

Earth

Moon

Lunar Phases

• When we see the Moon, we see the light from the Sun reflected off its surface– The illuminated side does not always face Earth– We see different amounts of the lit side as the Moon

orbits Earth

Why does the moon not look the same every night?

• Different phases of the moon

The Far Side of the Moon

• The full view of the far side of the moon is never visible from Earth• The far side was first photographed by the Soviet Luna 3 orbiter in 1959

Naming the phases of the moon.

Terminology for Moon Phases:

• Crescent – phases where the moon is less than half illuminated.

• Gibbous - phases where the moon is more than half illuminated.

• Waxing - "growing" or expanding in illumination

• Waning - "shrinking" or decreasing in illumination.

Phases

Phases in Motion

Waxing Gibbous

Waxing Cresent

Last Quarter

New Moon

Full Moon

Waning Cresent

Eclipses

• The Moon's orbit around Earth is tilted relative to Earth's orbit around the sun.

• Lunar Eclipses occur only at the time of the full moon.

• Solar Eclipses occur only at the time of the new moon.

• An eclipse can only happen when the sun, moon and Earth are in a nearly perfect straight line.

What happens more often, solar or lunar eclipses?

• Solar eclipses are fairly numerous, about 2 - 5 per year, but the area on the ground covered by totality is only a few km wide.

• In any given location on Earth, a total eclipse happens only once every 360 years.

• Eclipses of the Moon by the Earth's shadow are actually less numerous than solar eclipses; however, each eclipse covers about 1/2 the surface of the Earth. At any given location, you can have up to 3 lunar eclipses per year, but some years there may be none.

• In any one calendar year, the maximum number of eclipses is 4 solar and 3 lunar.

Lunar Eclipse• When the Earth is directly between the Sun and the

Moon • Total Eclipse - the entire moon passes through the

Earth’s shadow• Partial Eclipse - only part of the moon passes through

the Earth’s shadow

Lunar Eclipsehttp://www.youtube.com/watch?v=wuhNZejHeBg

Solar Eclipse

• When the moon is between the Sun and Earth• Only possible when there is a new Moon• Only the Corona of the Sun is visible

Solar Eclipse

Solar Eclipse

Tides & Tidal Force

• Gravity of moon and sun pull the Earth’s water toward them.

• This causes tides:– The rising and falling of the surface of large bodies of water

• This results in TWO high tides and TWO lows tides on Earth each day. The time between low and high tide is approximately SIX hours.

Tide

Tidal Force

• The side of the planet/moon closest to the other body experiences a tidal pull due to the force of gravity.

• When Sun and Moon are aligned then the effect on the tides is increased.

• When the Sun and Moon are perpendicular to one another the two gravitational pulls counteract each other and there are weaker tides formed.