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If you are outside this weekend make sure you look up at the moon in the night sky. If you see a full moon, all the better! But what does it mean when there is a full moon? Why do we always see different amounts of the moon on different days?

Since the beginning of human life, we have been looking up at this mysterious object in the sky and wondered about where it came from and why it is there. Test your “Moon” knowledge by trying to answer the following questions before you read the answers.

Why does the moon have phases? The different phases of the moon are caused by the relative positions of the earth, sun and moon. The moon orbits the earth approximately every 27 days, 7 hours, and 43 minutes. When the sun and the moon are on opposite sides of the earth, we see a “full moon” since the moon is fully exposed to sunlight. When the moon is between the earth and the sun, the moon is dark which is called a “new moon”. In between the “new moon” and “full moon” different portions of the moon are visible. This lunar phase is about 29.5 days.

Why do we always see the same side of the moon? Earth’s gravity has slowed down the moon’s rotational speed. The moon takes the same amount of time to rotate once on its axis as it does to complete one full orbit of the earth. This concept is a little tricky to grasp.

You can better understand this concept by using two round objects such as baseballs. Hold one ball stationary in one hand to represent the earth and hold the other ball in the other hand to represent the moon. Now, without twisting your wrist, make a complete circle with the “moon” ball around the stationary “earth” ball. It seems that people on earth should be able to see all the sides of the moon. But remember, the moon rotates on its axis while it rotates around the earth. Try the experiment again but this time slowly turn the “moon” ball as it circles the “earth” ball. If you time it right, you should be able to see why we only see the same side of the moon at all times.

How big is the moon? The moon is a little over 1/4 the size of earth, with a diameter of 2160 miles.

Is there weather on the moon like there is here on earth? The moon does not process any atmosphere so there is no weather like we experience here on earth. There is also no wind on the moon, so the footprints left by Neil Armstrong and Buzz Aldrin will be on the surface of the moon for centuries. The temperature on the moon also varies dramatically over the course of a day from 100 degrees Celsius in the afternoon to -175 degrees Celsius at night.

What types of features are on the surface of the moon? The moon is covered with interesting things such as craters, lava plains, and mountain ranges. The surface of the moon also has many other interesting characteristics that you should try to learn about in your science books.