Facts About the Moon & Optical Illusions

Facts about the Moons  and Its Optical Illusion


A composite photo of the moon from NASA.

Teaching materials and fun facts about the moon

As an Educator, working in the field, or looking to fill conversation, I frequently turn to subjects that are close at hand. Often it's cumbersome to carry objects on a trail, you can't always find certain plants or animals when you need them (a general rule of thumb), and sometimes you just need to keep people's minds busy to avoid kids wandering off, people losing attention, or just "losing" your audience all together. One of the constants you can always talk about, especially at dawn, dusk, or for evening programs is the Moon. No matter where you are in the world, there it is. On top of this, the new Next Generation Science Standards have a strong component of space literacy too. Specifically they are targeting 1st and 5th grades, middle school, and high school. This program includes determining phases of the moon and determining distances in space. In this blog post we'll explore some quick moon facts, a fun exercise in proportion and size, and I'll provide you with some books and lesson plans that I like for teaching about the moon.


The Moon as observed from the atmosphere of Earth (Photo: NASA).

How far away is the Moon?

According to NASA, the moon is about 384,400 km (238,855 miles). Here are some other facts about the moon:

  • The Moon is thought to have gotten its name from the Old English word mona. The Green name was mene, and the Latin name was mensis. It's no coincidence that the word moon and month sound about the same, because they come from the same roots.
  • At its farthest the Moon is 405,696 km (252,088 miles) away in its orbit (called the Apogee)
  • The orbital period of the moon is approximately 27.32 Earth days.
  • The gravity of the Moon is about 17% of Earth's, which means that if you weighed 150 lbs (68 kg) on Earth you would weigh about 25.5 lbs (11.6 kg) on the Moon.
  • Because of the weak gravity of the moon, if you were to throw a baseball on the Moon's surface, it would travel about 6-7x as far as on Earth. You could be an amazing player!
  • It's thought that the moon formed about the same time as the Earth, and that it was possibly made from a chunk of the Earth or from rock and other debris materials.
  • The mass of the moon is about 1.2% that of Earth, so the Earth is roughly 81x heavier than the Moon.
  • There is no "man in the moon" it's just craters and other materials that appear to look like a face.

The Dark Side of the Moon

If you're like me, you like Pink Floyd's "Dark Side of the Moon" album. But did you know that the song is actually misleading with its title? There really is no dark side of the moon. Because the moon orbits around the Earth in 27 days, and it spins at this same rate, it keeps the same side or face towards Earth while it orbits us. The speed of the Moon's rotation has led to the misconception that it does not rotate at all. But if the moon didn't spin on its axis at all then eventually we would see its far side, because the Moon is orbiting the Earth too.


Optical light dispersion used on the Pink Floyd cover of "Dark Side of the Moon." (Photo: Wiki Commons).

Another misconception is the one side of the moon never receives sunlight, this is not correct. The moon is continually rotating on its axis, so there is never any time when it is in permanent darkness. The only time the far side of the moon does not receive sunlight is during a Full Moon, when the Earth is between the Sun and Moon, and only the sunlit portion of the Earth is facing us.

Optical Illusions and the Moon

Have you ever looked at the moon on the horizon and noticed that it seems to be "huge" compared to when it is higher in the sky? You might think this is because of the refraction, or bending light, of our atmosphere and the sky. It's actually caused by an optical illusion. The moon is the same size the whole time, it's our eyes that are playing a trick! This is called the moon illusion or Ponzo illusion.

NASA moon

This photo illustrates how the moon, climbing into the sky, is actually the same size (Photo: NASA).

Mario Ponzo helped demonstrate this illusion in 1913, which shows that our minds often try to make sense of world by determining size based on the background behind an object.

Examine at the image below:


An illusion of the Ponzo illusion, which is believed to cause how we see the moon on the horizon as large (Photo: Wiki Commons).

The background of the two yellow lines makes it appear as if one is far away and one is closer. However, if you were to print this image out and measure the width of yellow lines with a ruler, you would find that the two lines are exactly the same size. Your perception of the lines is based on how your brain "reads" the object's background.

This phenomenon is thought to be why the moon looks larger on the horizon, and smaller as it climbs into the sky. You can prove this by trying the following:

1. Take a picture of the moon from the same location, at different times of night, and then measure the diameter of the moon in the picture. Phones don't have the same "translation" issues our brains do.

2. Kids love this one: Observe the moon on the horizon from an upright or standing position. Then turn your back to the moon, bend over, and look at the moon through your open legs. By changing your position you "short-circuit" the brain's typical response to size and orientation to "reading" the size of objects. By doing this, the moon will appear its actual size.

3. Hold your thumb up to the moon, and measure the moon using your thumbnail, from the same location, at different times of the night.

What is the Moon Phase Today?

The best resources I've found for Moon Phases are from the Moon Connection and LunaF.com.


The Moon's phases (Photo: NASA).

Full Moon Calendar

You can also find a nice full moon calendar, for this year and coming years, from the MoonPhases info website.

Resources for Understanding and Teaching about the Moon

CLICK ON THE IMAGE OF THE SIMULATOR BELOW to view how the phases of the moon appear from the Earth, the Sun, and Space.

Three Views Simulator

Click this image for a simulator of the phases of the moon.

Oreo Phases of the Moon:

OreoMoonPhases-300x226 Mr. Bensons Science Classroom

An example of an activity you can do with children, to learn the phases of the moon (Photo: Mr. Benson's Science).

How big would the Universe be if it was measured in pieces of toilet paper? This is a great activity!

Pinterest how big toilet paper

You can help students understand how far away the moon is by using toilet paper and modeling (Photo: Pinterest).

And just because I have music on my brain now....a little light entertainment!