The Moon, An Old Friend

     Dear Diary...

     Let's talk about the Moon. For astronomers, it's the Blue Planet's only natural satellite. For poets and musicians, it's an inspiration. For pirates, it's a nocturnal shepherd. For Germanics, Babylonians and Islam, it's a calendar. For ancient cultures, it was a celestial deity. For ocean tides, it's a force.

     The Moon is the fifth largest natural satellite in our Solar System, trailing behind Jupiter's Ganymede, Saturn's Titan (without taking its atmosphere into consideration), and again Jupiter's Callisto and Io. The Moon is also the second densest moon right after Io. To better visualize how big the moon is, this picture is pretty accurate:

     Let's start with the lunar phases. There are four main phases, each needs almost one week to take place, making the lunar cycle (or what's called a moonth) nearly 29.5 days old.

1. New Moon
2. First Quarter
3. Full Moon
4. Last Quarter

     When the moon appears to be growing, we say that it's waxing, when it appears to be shrinking, we say that it's waning. Enough with the vocabulary, this diagram says it all:

Phases of the moon

     What we see when we look up to the moon is basically a light show caused by the Sun's total or partial illumination of the moon, whenever the moon is in the Earth's shadow, a lunar eclipse occurs (that's almost once every six months). Only one half of the moon is illuminated by the sun, because it's tidally locked to the Earth meaning that the same side always faces the earth. This following simulation simplifies everything I wrote:

     It's the geometry of the Moon, the Sun and the Earth that entertains us with phases and eclipses. Now, the Moon crosses the Earth’s equator twice on every orbit once going up and once coming back down.
     One every six months or twice a year, the Moon finds itself in Earth's shadow thus causing a lunar eclipse, and often the Moon places itself between the Earth and the Sun, blocking it and thus causing a solar eclipse.
     This is the precise lining of what we call the Nodes, where the Moon’s orbit crosses the Earth’s equator. Of course the fellas at NASA who love drawing tables have lots of cool calculations on their eclipse website, check them out here. The next lunar eclipse will occur on the 4th of June of 2012, just one day before the transit of Venus, more on the transit of Venus can be found in one of my previous entries here. To further clarify, it’s not the crossing of the Equator that necessarily causes the Eclipse, although that can happen if you precisely have one at a Solstice (quick definition: the summer solstice and the winter solstice, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days). It’s actually the crossing of the Ecliptic which is the line that the Sun follows in the Sky that causes the Eclipses.

     Surely having a celestial body so close to our planet must amount to some kind of grande scale interaction, which brings us to tidal forces. So, the Moon is also guilty of changing tides (quick definition: the alternate rising and falling of the sea, usually twice in each lunar day at a particular place, due to the attraction of the moon and the Blue Planet). When the Moon is hovering above the earth, it's actually capable of exerting a gravitational force on the water in the sea puling at it causing a high tide. Because of the Earth's rotation, stuff is getting pulled up and carried away at the exact same time so High Tide is always a little bit ahead of where the Moon is. The Moon is going counter-clockwise around the planet Earth, so if you were somewhere outside of the system {Earth-Moon} (with your telescope), you'll see the High Tide in front of where the Moon actually is.
     The deformation of the Earth's surface because of the moon follows a circular pattern, where there's a high tide, a low tide, a high tide, and a low tide again closing the cycle. This cycle happens once every day.
     This is for the geek in you:

    This is to better visualize how the Moon's affecting the Earth, think of American football:

     An interesting astronomical fact is that the rotation of the Earth is getting slowed down because it's tidally locked to the Moon. This slowing of the Earth’s rotation with conservation of angular momentum requires that the Moon move to a larger distance away from the planet Earth. So, overtime, the Earth's rotating at a lower speed and the moon is moving further away, the Moon moves away from us 3 inches from the Earth each year. That's not enough to cause any major changes in our lifetimes, we're talking on astronomical scales, so some 50 billion years.

     Personally, I blame the Earth's pollution but I have no scientific proof to back that up, except that I believe that our planet stinks from outer space.
 

     The entire surface of the Moon has just been completely pulverized with craters, so it's very ugly (sorry poets, blame the Apollo missions). To be brief, just like the Earth, the moon gets hit with comets and asteroids every now and then. There are craters and mountains on the Moon, some places are always illuminated by the Sun like the mountains, other places never see the sunlight like deep craters. Most importantly, there is no proof of water on anywhere on the Moon.

    This is the APOD (astronomy picture of the day) of November 13 2005, for more photos of the Moon, go here. This is a time-lapse sequence shows what our Moon looks like during a lunation or a moonth.