The Moon

What causes the phases of the Moon? The appearance of the moon or its phases is dependent upon the relative positions of Earth, the Moon and the Sun.

Moon Phases The Moon is not visible from Earth during the new Moon phase as the illuminated portion of the Moon is facing the sun and the dark side is facing earth. During a full moon, when we see the entire illuminated portion of the moon: the sun, earth and moon are in direct alignment with the moon behind the earth. The Moon’s phases appear as the Moon moves in its orbit around the Earth. Each day, the Moon-Earth-Sun angle changes slightly, and a different portion of the Moon is illuminated.

The row of moons below shows how the moon would appear to an observer on earth. Phase 1 = New Moon Phase 3 = first quarter Phase 5 = full moon Phase 7 = last quarter (These are the four principal phases of the Moon- they occur at precise times on certain days of the lunar cycle) These principal phases occur when the Moon is in line with the Earth and Sun, or at right angles to the Earth-Sun line

The remaining 4 phases shapes’ vary with time, amount of illumination increasing or decreasing, depending on the phase. Phase 2 Phase 4 Waxing crescent Waxing gibbous Phase 6 Phase 8 Waning gibbous Waning crescent

What phase of the moon is this? Waxing gibbous, waxing crescent 3rd quarter.

Animations Moon phases http://www.sumanasinc.com/webcontent/animations/content/moonphase.html Sidereal and synodic months http://www.sumanasinc.com/webcontent/animations/content/sidereal.html

ECLIPSES

Occur when one celestial body blocks light from reaching another Different types of eclipses occur depending on what body casts the shadow, what body intercepts the shadow and what part of the shadow is intercepted.

LUNAR ECLIPSE The Moon passes through the Earth’s shadow. (SEM) Earth’s shadow falls on the moon. When the moon fits fully into Earth’s umbra =total lunar eclipse ( full moon phase). Usually red due to earth’s atmospheric aerosols. The change in size of the moon is due to its change in distance from the earth (apogee/perigee) The change in shape of the moon is due to the phase of the moon observed. Think aphelion and perhelion – which is closer? We see the phases because the moon is orbiting around the earth. The moon is illuminated by the sun.

SOLAR ECLIPSE Occurs in the new moon phase The moon blocks out the sun (SME) Occurs in the new moon phase Path of totality is the path on Earth where the total solar eclipse is visible.

Types of solar eclipses Type of solar eclipse seen depends on where on Earth the observer is. A person standing where the Moon’s umbra hits the Earth will see a total solar eclipse (leaving a corona)

People standing in the adjacent shaded region where Moon’s penumbra touches the Earth would observe only part of the Sun’s disk being covered by the Moon = partial solar eclipse

Tides What causes tides? They are caused by the gravitational pull of the moon and the Sun on the Earth. Spring Tides= when the earth, the moon and the sun are in alignment. High Tide = when the earth is facing the moon. Low Tide= occurs on the side of the earth not facing the moon.

Spring tide = highest high tide and lowest low tide. Neap Tide = lower high tide, higher low tide. The tides and currents are greatest during spring tides (full & new moon) and smallest during neap tides (first & third quarter). Tide height and current speed can increase by about 50% during spring tides. During a full moon the night high tide will be higher than the day high tide, while during a new moon the day high tide will be greater than the night high tide. The moon has the greatest effect on the tides. The sun has the second greatest effect and all the planets also affect the tides. The more these celestial bodies align the greater the gravitational pull and the higher the tides and the greater the currents.

Tide Wrap-up During which phase of the moon do neap tides occur? 1st and 3rd quarters. During which phase of the moon do the spring tides occur? New or full moon. How many tides in a day? Two high tides and two low tides. Why are there not exactly 12 hours between tides? Because the moon revolves around the earth while the earth rotates