Modelling phases of the moon

 In an earlier video, we explored the movement of earth and moon with respect to the SUN. 

Red ball representing the sun can be replaced with the flashlight of the cell phone. Now we can observe the play of shadows as Earth and Moon change positions.  This arrangement does not allow us to view the moon from Earth. Let us place another phone in place of earth and a larger ball in place of a small moon. 

In fact we don't need this setupl.  Instead, we will use the flashlight of this phone to represent sunlight.

On this turntable made from corrugated sheet, a small plastic ball represents the moon. 

This second phone represents Earth. Camera on this second mobile phone will enable us to view phases of the moon as it revolves around the Earth. 

Height of the light source needs adjustment at some locations to avoid the shadow of Earth on the moon. 

Let us start with the New Moon. 

For better viewing, we will move the flashlight farther. 

Frame on the left side shows the top view while the frame on the right side shows the moon as seen from Earth.

Like Earth, the Moon has a day side and a night side, which change as the Moon rotates. The Sun always illuminates half of the Moon while the other half remains dark, but how much we are able to see of that illuminated half changes as the Moon travels through its orbit. We call it a Phase. 

The Moon has eight phases in a lunar month: four primary and four intermediate phases.

There are eight phases.  in order, new Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, third quarter and waning crescent. The cycle repeats once a month (every 29.5 days).

New Moon

This is the invisible phase of the Moon, with the illuminated side of the Moon facing the Sun and the night side facing Earth. In this phase, the Moon is in the same part of the sky as the Sun and rises and sets with the Sun. Not only is the illuminated side facing away from the Earth, it’s also up during the day! Remember, in this phase, the Moon doesn’t usually pass directly between Earth and the Sun, due to the inclination of the Moon’s orbit. It only passes near the Sun from our perspective on Earth.

Waxing Crescent

This silver sliver of a Moon occurs when the illuminated half of the Moon faces mostly away from Earth, with only a tiny portion visible to us from Earth. It grows daily as the Moon’s orbit carries the Moon’s dayside farther into view. Every day, the Moon rises a little bit later.

Waxing Gibbous

Now most of the Moon’s dayside has come into view, and the Moon appears brighter in the sky.

Full Moon

This is as close as we come to seeing the Sun’s illumination of the entire day side of the Moon (so, technically, this would be the real half moon). The Moon is opposite the Sun, as viewed from Earth, revealing the Moon’s dayside. A full moon rises around sunset and sets around sunrise. The Moon will appear full for a couple of days.

Waning Gibbous

As the Moon begins its journey back toward the Sun, the opposite side of the Moon now reflects the Moon’s light. The lighted side appears to shrink, but the Moon’s orbit is simply carrying it out of view from our perspective. The Moon rises later and later each night.

Last Quarter

The Moon looks like it’s half illuminated from the perspective of Earth, but really you’re seeing half of the half of the Moon that’s illuminated by the Sun ― or a quarter. A last quarter moon, also known as a third quarter moon, rises around midnight and sets around noon.

Waning Crescent

The Moon is nearly back to the point in its orbit where its dayside directly faces the Sun, and all that we see from our perspective is a thin curve.

Variations.

You can perform this activity with balls of different sizes, changing the position of the SUN as well.

Do try this at home.

I captured phases of the moon with my camera during this activity as well.

Ball with indentations was 3D printed for this activity.

Thank You.