Moons of our Solar System
Moons of our Solar System

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Moons of our Solar System

2.11 How the Moon’s phases look from the Earth

You see the Moon at its best after dark, when the Sun is below the horizon. Because the Moon orbits in almost the same plane as the Earth’s Equator, the phases of the Moon look different depending on which side of the Equator you are standing on.

Described image
Figure 33 View of the Moon’s phases from the Northern Hemisphere (top) and from a point at the same latitude in the Southern Hemisphere (bottom)

As seen from the Northern Hemisphere in Figure 33, the Moon rises in the east and moves left to right, passing to your south across the sky until it sets in the west.

However, in the Southern Hemisphere, the Moon is seen in the north at night. It rises in the east and moves right to left across the sky, passing to your north before sinking below the horizon in the west.

When the Moon’s phase is a crescent, the direction to the Sun is away from the sunlit part of the crescent, at a right angle to the horns of the crescent. If the Sun is below the horizon, as it needs to be for the crescent Moon to be visible, this means that the sunlit part of the crescent must be tilted downwards. Therefore, for observers in the Northern Hemisphere, a waxing crescent forms a growing ‘D’ shape (by which we mean the mirror-image of a ‘C’) with the curve tilted slightly down, and a waning crescent forms a ‘C’ shape (also with the curve tilted slightly down). South of the Equator, the Moon waxes in a growing ‘C’, and wanes as a narrowing ‘D’, with the curve tilted slightly down in each case.

However, look for cartoon drawings of the Moon on the internet, or ask a friend to sketch a crescent Moon for you, and the chances are you will end up with a ‘C’ shape - despite the fact that most people live in the northern hemisphere and see the evening ‘D’ shape crescent far more often than the morning ‘C’ shape crescent. Is this your experience? Can you account for it?

If you wanted to look into this further, you might find the following link of interest: Even The Simpsons gets it wrong [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] . A C-shaped crescent Moon was wrongly shown in the evening sky in Springfield, where the Simpsons live (supposedly in the USA) during a guest appearance by a space entrepreneur, sparking amusing comment in the Bad Astronomy blog.

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