A Halloween Moon

It's nights like this that make us think of treats and dressing up in fun costumes. But, do you also think of... the Moon? When you imagine the perfect sky scene for Halloween, what is in your mind? Some clouds with a full Moon in the background? Maybe a witch on a broom in front of a crescent Moon? I remember the Halloween decorations we had when I was a kid. I would get them out every year and put them up in the windows in our house, and if the decoration had a Moon on it, it was always a crescent or full Moon.

Does the Moon always look like a crescent or full Moon on Halloween? Let's do an activity to figure this out. Grab a lamp and a round ball, and turn the light on so it is the only light in a darkened room (you may need to take the shade off the lamp... be careful; lit light bulbs might get hot). Look at the ball. Do you see that half of it is lit by the lamp? Walk around the lamp as you hold the ball. Do you see that half of the ball is always lit by the lamp? Turn the ball and observe how it appears. No matter how you turn the ball, half of it is always lit by the lamp. Which half? The half that is facing the lamp. Now, put the ball somewhere in the room where you can walk around it and it doesn't roll off onto the floor. Move around the ball and observe how it appears. Depending on where you are in relation to the lamp and the ball, you should see more or less of that lit half.

Crescent and full Moon are called "phases" of the Moon. A Moon phase is the amount of the Moon that is lit by the Sun that can be seen from Earth. Half of the Moon is always lit by the Sun. How much of that lit half that we can see from Earth is the phase of the Moon.

The phases of the Moon do not coincide with the calendar months. It takes about 29.5 days for the Moon to travel once around the Earth and go through a complete cycle of phases. Our calendar months can be 28, 29, 30, or 31 days long, so while the full Moon might be on your birthday this year, it won't be the same phase next year. You can look up the phase of the Moon for any day of the year using the U.S. Naval Observatory's website.

Questions? Email me! astroeducator {at} aol {dot} com.

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