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Moon Phases, Eclipses and Tides. 21.4. Moon Phases. Caused by changing relative position of the moon, Earth and Sun. Moon does not create its own light, it reflects the light from Sun.
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Moon Phases • Caused by changing relative position of the moon, Earth and Sun. • Moon does not create its own light, it reflects the light from Sun. • The lit part of the moon we see is caused by the moon’s position relative to the sun as it revolves around Earth. • Half of the moon’s surface is always lit. The phase is the portion of that lit half that we can see from Earth.
More Moon Phases • In new moon, the moon is between Earth and sun and we cannot see the lit portion • In Waxing phases, the lit portion of the moon that we see is increasing each day. • Full moon – the Earth is between the sun and moon. • In Waning phases, the lit portion of the moon that we see decreases each day until new moon. • Cycle lasts approx. 28 days
Solar Eclipses • Occur during new moon phase when Moon is between Earth and Sun. During the day • The moon blocks light from the sun during the day as its shadow crosses the Earth as it rotates on its axis. • Umbra is the darkest and smallest part of the shadow and the area of total eclipse. Sun’s rays are blocked. • Penumbra is less dark and is the area partial eclipse – all of the sun’s rays are not blocked. It covers a much wider area.
Lunar Eclipse • Happens at full moon time at night. Earth passes between moon and sun and casts its shadow on the moon. (red glow) • Umbra is the cone of maximum light blockage and darkest shadow. It is the area of total lunar eclipse. • Penumbra is a larger area of lighter shadow and is the area of partial lunar eclipse • See diagrams p. 24 and 25
Tides • Tides are caused mainly by differences in how much the moon’s gravity pulls on different parts of the Earth. • The water bulges on the side nearest the moon, creating high tide. • The water is pulled from both sides creating low tides in those locations. • The moons gravity attracts the earth, leaving the bulge of water on the side of the Earth opposite the moon. • There are 2 high tides and 2 low tides each day. • Spring tide – highest high tide and happen at new moon phase when Sun and moon are on the same side of Earth. • Neap Tides – lowest high tides and happen at first and third quarter moon when sun and moon are pulling against each other at right angles. P. 26&27