Editing Lunar phase (section)

=== Waxing and waning ===
[[File:The Moon's Phases as Seen from Space.ogv|thumb|left|This video provides an illustration of how the Moon passes through its phases &ndash; a product of its orbit, which allows different parts of its surface to be illuminated by the Sun over the course of a month. The camera is locked to the Moon as Earth rapidly rotates in the foreground.]]
[[File:Moon Phase Diagram for Simple English Wikipedia.GIF|thumb|right|Diagram of the Moon's phases: The Earth is at the center of the diagram and the Moon is shown orbiting.]]
When the Sun and Moon are [[conjunction (astronomy)|aligned on the same side]] of the Earth (conjunct), the Moon is "new", and the side of the Moon facing Earth is not illuminated by the Sun. As the Moon ''waxes'' (the amount of illuminated surface as seen from Earth increases), the lunar phases progress through the new moon, crescent moon, first-quarter moon, [[wikt:gibbous|gibbous]] moon, and full moon phases. The Moon then ''wanes'' as it passes through the gibbous moon, third-quarter moon, and crescent moon phases, before returning back to new moon.

The terms ''old moon'' and ''new moon'' are not interchangeable. The "old moon" is a waning sliver (which eventually becomes undetectable to the naked eye) until the moment it aligns with the Sun and begins to wax, at which point it becomes new again.<ref>{{cite web |title=Free Astronomy Lesson 7 - The Phases of the Moon |url=http://www.synapses.co.uk/astro/moon2.html |access-date=2015-12-28 |archive-url=https://web.archive.org/web/20230414073024/http://www.synapses.co.uk/astro/moon2.html |archive-date=2023-04-14 |url-status=live}}</ref> ''Half moon'' is often used to mean the first- and third-quarter moons, while the term ''quarter'' refers to the extent of the Moon's cycle around the Earth, not its shape.

When an illuminated hemisphere is viewed from a certain angle, the portion of the illuminated area that is visible will have a two-dimensional shape as defined by the intersection of an [[ellipse]] and circle (in which the ellipse's [[major axis]] coincides with the circle's diameter). If the half-ellipse is convex with respect to the half-circle, then the shape will be gibbous (bulging outwards),<ref>{{cite web |title=Gibbous Definition & Meaning |url=https://www.dictionary.com/browse/gibbous |website=[[Dictionary.com]] |archive-url=https://web.archive.org/web/20230421145830/https://www.dictionary.com/browse/gibbous |archive-date=2023-04-21 |language=en |quote=Origin of gibbous: 1350–1400; Middle English <Latin gibbōsus humped, equivalent to gibb(a) hump + -ōsus-ous |url-status=live}}</ref> whereas if the half-ellipse is concave with respect to the half-circle, then the shape will be a [[crescent]]. When a crescent moon occurs, the phenomenon of [[earthlight (astronomy)|earthshine]] may be apparent, where the night side of the Moon dimly reflects indirect sunlight reflected from Earth.{{sfn|Asmelash|Allan|2019|}}
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