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History

La Luna, My Moon and its Phases

The moon, it is always there in the sky watching us. Its no wonder that stories have been weaved through our history that tell of the mystical powers of the moon. One of the oldest depictions of the of the moon is located not too far from here in Knowth. The central chamber of the burial mound is said to hold this nearly 5000 year old map of the moons surface. Those who have seen it say that it has pits and mountains representing the craters and mountains we can see on the moon with the naked eye. The rest of the burial mound is decorated with circular and spiral patterns, all believed to be various depictions of the moon.

The truth is however, that the moon is no more mystical then any rock in the forest. The moon isn’t like all the twinkling stars in the sky, it doesn’t shine bright, in fact it doesn’t shine at all. I’m not trying to say that the moon isn’t important to our everyday lives, it is responsible for the ocean tides, changing day lengths and the magnificent eclipses that make us stop in our tracks.

You might wonder how the moon was created, of course no one knows for sure. There are theories that it was created at the same time as the Earth as just extra material that was spun out of Earth’s gravitational field. However, the most widely accepted theory is that there was a massive impact from an object the size of Mars while the Earth was still forming. This impact threw debris into space, and as the Earth reformed the remaining material collected into what we know as the moon.

Did you know that we always see the same side of the moon? The moon’s rotational period, or lunar day, is exactly the same as the lunar orbital period, or the time it takes to go around the Earth once. The Moon is in a geosynchronous orbit meaning it is locked in the same orientation with the Earth.

The moon is the brightest object in the sky, second only to the sun, however if it weren’t for the sun we wouldn’t be able to see it at all. The surface of the moon is actually very dark and it doesn’t produce any of its own light. The dust on the moons surface is very similar in color to coal, however even this dark dust can reflect a small amount of light. The moon reflects most of its light directly back towards the sun. This reflection towards the sun is what causes phases of the moon. As the moon orbits around the Earth, the angle of the sun to the moon to the Earth changes. In the diagram below you can see all the phases of the moon.

There are two types of eclipses, solar and lunar. Lunar eclipses happen when the Earth’s shadow blocks the light from the sun during its full moon phase. Since the shadow of the Earth is larger than the viewing disk of the moon, the whole moon goes dark. A solar eclipse happens when the Moon passes into the path of the suns light to the Earth during the new moon phase. The Moons shadow is much smaller then light coming from the sun, so thats why a solar eclipse has a specific viewing area across the Earth’s surface.

Long ago, Chinese people used to think that solar eclipse was a dragon swallowing the sun. They would make noise by banging on drums and yelling to try and scare the dragon away. Of course solar eclipses are only temporary, so the sun would always return.

Want to create your own eclipse?

Materials:

tennis ball, ping pong ball, flashlight and a table with a table cloth

Procedure:

  1. Place the tennis ball about two feet away from the flashlight, and the ping pong ball in between at about the one foot point. 
  2. Make the room dark.
  3. Turn the flashlight on  and make sure its pointed at the tennis ball.
  4. Move the ping pong ball around and observe where the shadow falls.
  5. The tennis ball represents Earth, the ping pong ball represents the Moon, and the flashlight is the Sun.
  6. What happens when you place the Moon on the other side of the Earth?
  7. If you would like to observe the phases of the moon for yourself, slowly move the ping pong ball in a circle around the tennis ball and observe how the light from the flashlight looks on it.