Moon • Any natural satellite that orbits a planet is called a moon. • We call our moon • Moon
Moon • Our Moon takes about 27 1/3 Earth days to revolve around our planet once. • As it revolves we only see one side of the Moon.
Moon • If it did not rotate at all we would see different sides during the month. • If it rotated quickly we would also see different sides during the month. • We only see one side because it rotates at the same rate as it revolves.
Moon • Moon revolution 27 1/3 days • Moon rotation 27 1/3 days
Moon • When we observe the Moon over a month it appears to change. • We call these change phases.
Moon • The Moon does not give off its own light. • The lit surface is sunlight reflected off the surface. • We see different phases because of the angles that the moon makes with the Earth and Sun during each month.
Moon • When viewed from above it looks like the Moon should disappear behind the Earth when they are in a line. • It doesn't because the Moon’s orbit is tilted about 5 degrees to the plane of the Earth’s orbit.
Phases of The Moon • When the Sun, Moon and Earth are in a line we are looking at the unlit side of the Moon. • The Moon is above the horizon from sunrise to sunset. • The result is we can not see the Moon. • We call this phase New Moon.
Phases of The Moon • As the Moon moves around the Earth the right edge starts to come in view. • This is called a waxing crescent. • Waxing means it is growing larger.
Phases of The Moon • As it continues we eventually see half of the lit side. • We call this first quarter. • The Moon rises about noon and sets about midnight.
Phases of The Moon • As the Moon continues we see almost all of the lit side. • This is called a waxing gibbous.
Phases of The Moon • As the Moon continues its orbit around the Earth we see the entire lit side. • This is the Full Moon phase. • The Moon rises around sunset and sets around sun rise.
Phases of The Moon • As the Moon continues we start to see less of the lit side. • Now the left side is fully lit and the right side is disappearing. • This is called waning.
Phases of The Moon • As the Moon continues we see Third or Last Quarter. • The Moon rises about midnight and sets about noon.
Phases of The Moon • Finally we see a small sliver lit on the left side. • This is the waning crescent.
Phases of The Moon • This whole process from New Moon to New Moon takes 29 ½ days. • Wait…Moon takes 27 1/3 days to revolve but 29 ½ days between phases?
Phases of The Moon • Remember the Earth is revolving around the Sun while the Moon is revolving around the Earth so the Moon actually has to move further to line up with the Sun again.
Moon and Calendars • You may have noticed that there is a close relationship to the time from New Moon to New Moon (29 ½ days) and a Month. • That is because our months were originally determined by the movement of the moon.
Moon and Calendars • You will also notice it is about 7 days between each major phase of the Moon. • This is where we get our weeks.
Eclipses • The path that the Earth takes around the Sun is called the Ecliptic. • Twice a month the Moon’s orbit crosses the ecliptic at points called nodes. • If the Moon is at a node at either New Moon or Full Moon an Eclipse occurs.
http://astrowww.astro.indiana.edu/~classweb/a100s13426/APPLETS/Chapter2/assets.htmhttp://astrowww.astro.indiana.edu/~classweb/a100s13426/APPLETS/Chapter2/assets.htm Open site & click on node applet.
Eclipses • Because the Earth’s shadow is large and the Moon is small lunar Eclipses are more commonly observed across the Earth. • A lunar eclipse occurs at Full Moon and is when the Moon is blocked by the Earth’s shadow.
http://astrowww.astro.indiana.edu/~classweb/a100s13426/APPLETS/Chapter2/assets.htmhttp://astrowww.astro.indiana.edu/~classweb/a100s13426/APPLETS/Chapter2/assets.htm Open site & click on eclipse applet.
Eclipses • A solar eclipse is when the Sun is blocked out by the Moon’s shadow. • This only occurs at New Moon. • Because the Moon is very small and the Sun is very large you must be lined up in just the right spot to see a solar eclipse.
Eclipses • Occasionally the Moon is at apogee (farthest from the Earth) during a solar eclipse. • When this happens you see a ring (annulus) of the Sun around the Moon. • This is called an annular eclipse. • This is what we saw here in 1994.
Odd Facts • The Moon is receding from the Earth at 1.5 inches a year. • Because of this the last total solar eclipse visible from the surface of the Earth will take place 620 million years from now. • All Solar Eclipses will be annular eclipses after that.