We can’t take our eyes off it, it helps control our tides, and wolves howl at it; can you name what “it” is? You probably guessed correctly, it’s Luna, also known as the moon! The moon is the largest satellite of Earth, and one of the only natural satellites. This means that there may be other satellites out there orbiting around Earth (thanks to space junk and our cell phone providers), but it is by far the largest and amongst the only that came from space to orbit our home planet. Our moon is also the brightest object in our night sky, so bright in fact that you can sometimes see it during the day. However, the moon seems to be constantly changing. How can that be possible?
To demonstrate what is happening, you can do an easy experiment at home. All you need is a single light source (representing the sun), your face (representing Earth), and a ball or your fist (modeling the moon).
Earth’s gravity has the moon tidally locked, meaning the same half of the moon is always facing Earth, and the other half is always facing away (the dark side of the moon). Since it is tidally locked, your model of the moon does not need to spin. All you have to do now is put your moon between your face and model of the sun and start to rotate counterclockwise (the same direction that Earth spins).
When the moon is between the sun and the Earth, light from the sun cannot reflect from the moon to Earth. This phase is called a “New Moon”. As you keep rotating you will first see a waxing crescent, then: the first quarter, waxing gibbous, full moon (Earth is between the moon and the sun), waning gibbous, third quarter, waning crescent, then back to New Moon. If you keep rotating the cycle will continue on and on. For our real moon this cycle will take about 29 days to be completed.
You can easily keep track of this cycle on your own as well. All you need to do is step outside each night and make some observations. Take note of what the day and time is, and what the moon looks like to you. Once you have done this for a couple of weeks you should be able to predict what you will see next! So go ahead, give it a try for yourself and have fun.
Written by: Mimi Garai