Astronomy 04 The Solar System Chapter 3: “The Cycles of the Moon”

Chapter 3: “The Cycles of the Moon” The Moon travels around the Earth once every 27 1/3 days. This cycle is know as the Sidereal Period.

Chapter 3: “The Cycles of the Moon” As the Moon orbits Earth, it displays different phases which repeat every 29 ½ days. This cycle is known as the Synodic Period.

New Moon occurs when the Moon is between the Earth and Sun. No Moon can be seen in the sky at this time.

First Quarter Moon occurs when the Moon is at 90 degree angle with the Earth and Sun. We see a half Moon at this time.

Full Moon occurs when the Moon is directly opposite the Sun as viewed from Earth. We see the fully illuminated hemisphere of the Moon at this time.

Third Quarter Moon occurs when the Moon is again at a 90 degree angle with the Earth and Sun. We see a half Moon at this time.

Chapter 3: “The Cycles of the Moon” The Moon rotates on its axis in exactly the same amount of time it takes to orbit Earth (27 1/3 days). This is called synchronous rotation.

Chapter 3: “The Cycles of the Moon” The gravitational pull of the Sun and Moon on Earth produces ocean tides. There are 2 high and 2 low tides daily.

Chapter 3: “The Cycles of the Moon” Spring Tides are highest and lowest tides that occur at times of Full and New Moons. Neap Tides are next highest and lowest tides which occur at times of the First and Last Quarter Moons.

Total Eclipse of the Sun

Chapter 3: “The Cycles of the Moon” A lunar eclipse occurs when the earth’s shadow almost completely blocks the Moon from view A solar eclipse occurs when the Moon blocks the Sun from view. Solar or lunar eclipses can be partial or total.

Chapter 3: “The Cycles of the Moon” A lunar eclipse occurs when the Moon is at its Full Phase and at one of the nodes in its orbit, the Full Moon passes through Earth’s shadow and a lunar eclipse occurs on Earth.

Lunar and solar eclipses dn’t occur every New and Full Moon because the orbit of the Moon around the Earth

Chapter 3: “The Cycles of the Moon” The Moon does not usually disappear from view during an eclipse but turns a rosy red color. Lunar eclipses are always visible over large areas of Earth and for period of several hours.

Chapter 3: “The Cycles of the Moon” A solar eclipse occurs when the Moon is at its New Phase and at one of the nodes in its orbit, the New Moon casts a small shadow on Earth. Within this shadow observers see a Solar Eclipse as the Moon block the Sun from view.

Chapter 3: “The Cycles of the Moon” Features of a Total Solar Eclipse: Sky darkens to deep twilight. Planets and stars come into view. Corona, chromosphere and prominences appear around Sun. Bailey’s Beads or a Diamond Ring may be seen at the beginning and end of totality.

The Diamond Ring Effect

Chapter 3: “The Cycles of the Moon” If, in addition to the above two circumstances, the Moon is at apogee in its orbit, places on Earth will experience an Annular Eclipse. If, in addition to the above two circumstances, the Moon is at perigee in its orbit, places on Earth will experience the longest possible duration of a Total Solar Eclipse – 7 ½ minutes ! Solar eclipses are always visible over very small areas of Earth and for very short times.