Moons • Moons rotate around their parent planet. • Earth has one moon, but some planets have over 50. • Only Mercury and Venus do not have any moons.
Moon Facts • The Moon was created when a rock the size of Mars slammed into Earth, shortly after the solar system began forming about 4.5 billion years ago, according to the leading theory. • The Moon's heavily cratered surface is the result of intense pummeling by space rocks between 4.1 billion and 3.8 billion years ago. • The scars of this war, seen as craters, have not eroded much for two main reasons: The Moon is not geologically very active, so earthquakes, volcanoes and mountain-building don't destroy the landscape as they do on Earth; and with virtually no atmosphere there is no wind or rain, so very little surface erosion occurs. • As you read this, the Moon is moving away from us. Each year, the Moon steals some of Earth's rotational energy, and uses it to propel itself about 3.8 centimeters higher in its orbit. Researchers say that when it formed, the Moon was about 22,530 kilometers from Earth. It's now more than 450,000 kilometers away. • Basically no atmosphere. Some carbon gases, but very little of them. Pressure is about one-trillionth of Earth's atmospheric pressure.
Phases of the Moon • The new moon occurs when the moon is positioned between the earth and sun. The three objects are in approximate alignment . The entire illuminated portion of the moon is on the back side of the moon, the half that we cannot see. • At a full moon, the earth, moon, and sun are in approximate alignment, just as the new moon, but the moon is on the opposite side of the earth, so the entire sunlit part of the moon is facing us. The shadowed portion is entirely hidden from view. • The first quarter and third quarter moons (both often called a "half moon"), happen when the moon is at a 90 degree angle with respect to the earth and sun. So we are seeing exactly half of the moon illuminated and half in shadow. Crescent - refers to the phases where the moon is less than half illuminated. Gibbous - refers to phases where the moon is more than half illuminated. Waxing - essentially means "growing" or expanding in illumination Waning - means "shrinking" or decreasing in illumination.
Effect of the Moon on Earth • Tides are another kind of wave motion in the ocean. Tides are a change in the ocean water level, typically reaching a high and low level twice a day usually occurring about six hours apart. • Tides result from the pull of gravity; on the earth alone, between the earth and moon and between the earth and the sun. • The gravitational pull of the sun on the earth is about 178 times stronger than the gravitational pull on the earth from the moon. However, because of the close proximity of the moon, when compared to the sun, the tidal pull by the moon is over twice that of the sun. • The result of this tidal pull is a bulge in the ocean water almost inline with the position of the moon; one bulge toward the moon and one on the opposite side of the earth, away from the moon. When we observe the tides what we are actually seeing is the result of the earth rotating under this bulge
Spring Tide When the moon is full or new, the gravitational pull of the moon and sun are combined. At these times, the high tides are very high and the low tides are very low. This is known as a spring high tide. Spring tides are especially strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the Moon are in a line. Spring tides occur during the full moon and the new moon.
Neap Tide During the moon's quarter phases the sun and moon work at right angles, causing the bulges to cancel each other. The result is a smaller difference between high and low tides and is known as a neap tide. Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons.
Eclipses • The umbra is the darkest part of a shadow. From within the umbra, the source of light is completely concealed by the occulting body. In astronomy, an observer in the umbra is said to be experiencing a total eclipse. • The penumbra is the region in which only a portion of the occulting body is obscuring the light source. An observer in the penumbra experiences a partial eclipse.
Lunar Eclipse • Lunar eclipses occur when the Moon passes through the Earth's shadow. • Since this occurs only when the Moon is on the far side of the Earth from the Sun, lunar eclipses only occur when there is a full moon. • Unlike a solar eclipse, an eclipse of the Moon can be observed from nearly an entire hemisphere. For this reason it is much more common to observe a lunar eclipse from a given location. • A lunar eclipse also lasts longer, taking several hours to complete, with the process usually averaging anywhere from about 30 minutes to over an hour. • There are three types of lunar eclipses: • Penumbral, when the Moon crosses only the Earth's penumbra; • Partial, when the Moon crosses partially into the Earth's umbra; • Total, when the Moon circles entirely within the Earth's umbra. During a total lunar eclipse, however, the Moon is not completely dark. Sunlight refracted through the Earth's atmosphere intersects the umbra and provides a faint illumination.
Solar Eclipse • A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured. • This can only happen during a new moon, when the Sun and Moon are in conjunction as seen from the Earth. • At least two and up to five solar eclipses occur each year on Earth, with between zero and two of them being total eclipses. • Total solar eclipses are nevertheless rare at any location because during each eclipse totality exists only along a narrow corridor in the relatively tiny area of the Moon's umbra. • A total solar eclipse is a spectacular natural phenomenon and many people travel to remote locations to observe one. The most recent solar eclipse occurred on August 1, 2008, and was a total eclipse. • In ancient times, and in some cultures today, solar eclipses have been attributed to supernatural causes. Total solar eclipses can be frightening for people who are unaware of their astronomical explanation, as the Sun seems to disappear in the middle of the day and the sky darkens in a matter of minutes.