Phases of the Moon

Each day we see the moon take a different shape in our sky, called phases. Māori have a name for each phase and have carefully observed the pattern of how the changing of phases repeats every 30 days. This is similar to many other cultures around the world, who have also observed this same pattern.

This happens because the Moon does not emit light itsef. The 'moonlight' we see is actually light from the Sun reflected off one side of the Moon. Our view of the Moon changes as it revolves (orbits) around the Earth. When we see more of the sunlit side, the shape of the Moon appears like an oval or circle, such as the phases called Ōhua, Turu and Takirau. When we see more of the shadowed side, the shape of the Moon appears like a crescent or sliver, such as the phases called Tirea, Okoro and Ōtane. 

Internationally, the phases of the Moon are broken into 8 types instead, as shown inthe diagram below. 

• When the Moon's phase appears to be getting bigger, international astronomers refer to this as 'waxing' until it reaches the Full Moon phase. 

• When it looks like it's getting smaller, it is called 'waning' until it reaches the New Moon phase. 

Activity: Moon Phases Simulator

Use the interactive below or click on this link: https://www.earthspacelab.com/app/moon-phases/ 

• Set the "Select a place on the Earth" to Southern Hemisphere (if you wish to view the Moon from the perspective of New Zealand. 

• Tick the "Show the sunbeams direction" box.

• Observe the Moon phase as viewed from the Earth (top left hand box) and explain why we see this moon phase. 

Activity: Lunar Phase Simulator (with Horizon Diagram)

Use the interactive below or click on this link: https://ccnmtl.github.io/astro-simulations/lunar-phase-simulator/ 

• I recommend ticking the box for "Show time tickmarks"

• Drag the Animation rate slider to the left, to slow it down (so it's not dizzying!) 

• Click "Start Animation".

Activity: Moon Phases Simulation Viewed from Earth and Space

Use the interactive below or click on this link: https://www.pbslearningmedia.org/resource/buac19-35-sci-ess-earthsunmoon35model/moon-phases-simulation-viewed-from-earth-and-space/

• This simulation is different to the ones above because you also have a view of both the Sun and Moon's apparent position in the sky (as viewed from Earth). 

• Explain why some phases of the Moon appear during the daytime, and why some phases of the Moon appear only at nighttime.

• How do your observations of the Moon in this model compare with observations of the Moon from your location?

• What did you notice about when the Moon rose and set in the top part of the digital model? Use the diagram of the Earth–Sun–Moon system on the bottom to help you explain moonrises and moonsets.

• How does the Moon appear to move across the sky? How does the diagram at the bottom of the model help explain the path of the Moon?

• What would happen if Earth did not rotate on its axis but the Moon continued to orbit Earth? How would the sky appear differently for the observer?

• How would the sky appear differently for the observer over time if the Moon did not orbit Earth but instead stayed in one spot next to it?

• Find the two quarter Moons that appear at opposite points in the lunar cycle. What do you notice about which part of the sunlit half is visible from Earth? How does the Earth–Moon system in the model help you explain that difference?

Activity: Sun, Moon & Earth Position 3D Simulation

Use the interactive below or click on this link: https://en.tutiempo.net/astronomy/sun-earth-moon-3d.html#UTC20250704T2248

• This simulation is different to the ones above because you view the position of the Sun, Moon and Earth from space, in 3D, from all angles.

• Bring up the menu on the bottom of the screen, and change the following settings:

  • • Toggle the box to 'Bring the Sun closer'

    • Toggle the box to 'Fix Earth' - this allows you to not lose your point of view each time you click to change the date/time, however it makes it look like the Sun is revolving around the Earth (which it is not).

• Change the date to today. 

  • • In your book, draw where the Moon is currently, compared to the Sun and the Earth. 

    • Do you think we can see the lit side of the Moon today (during the day)? Explain your answer. 

    • Would we be able to see the Moon tonight? Explain your answer. 

• Bring up the menu on the bottom of the screen, and scroll down to the Sample Dates. Click on each date to see examples of a total solar eclipse and a total lunar eclipse.