Moon phases: why the Moon changes shape

Also called

moon phases · phases of the moon · lunar phases · why does the moon change shape · new moon · full moon · crescent moon · gibbous moon · first quarter · last quarter · waxing and waning · synchronous rotation · same side of the moon · chandrama ki kalaayen · चंद्रमा की कलाएँ · अमावस्या · पूर्णिमा · synodic month · lunar month

Topics

• The Moon does not make its own light; it shines because sunlight falls on it
• Half of the Moon is always lit by the Sun, whatever the phase
• Phases depend on how much of that sunlit half faces Earth as the Moon orbits
• Ordinary phases are not caused by Earth's shadow; a lunar eclipse is a separate, rarer event
• The eight named phases: new Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous…
• At first and last quarter half of the visible disk is lit; "quarter" means a quarter of the way through the cycle
• The phase cycle (synodic month) takes about 29.5 days; one orbit relative to the stars (sidereal month) takes about…
• The Moon turns once on its axis for each orbit, so the same face always points toward Earth
• The Moon's orbit is tilted about 5 degrees, so most full Moons miss Earth's shadow and most new Moons miss the Sun
• Seen from the Southern Hemisphere the Moon appears upside down, so a waxing Moon is lit on the left instead of the right

About this model

A GLB file of about 1444 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Sun, Earth and Moon 3D models and textures: NASA Visualization Technology Applications and Development (VTAD), science.nasa.gov; textures re-mapped and resized for Lably. Model, guides and animation made for Lably. No NASA endorsement is implied. | Sun, Earth and Moon surface pictures: NASA Images and Media Usage Guidelines (educational use with credit; no NASA endorsement implied). Everything else (globe meshes, shades, orbit, guides, sky-view panel, phase clock, base) and all animation: original for Lably. No CC BY-SA (Tactiles) assets are used.

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