Moon Phase Calculator and Guide
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Understanding Moon Phases
The phases of the Moon are the different ways the Moon looks from Earth over about a month. These changes aren't because the Moon is actually changing shape, but because we see different amounts of the Moon's sunlit side as it orbits Earth.
The Moon itself doesn't produce light; it shines by reflecting sunlight. As the Moon travels around Earth, the angle between the Sun, Earth, and Moon changes, causing us to see varying portions of the illuminated surface.
The Eight Main Phases:
New Moon 🌑
The Moon is between the Earth and the Sun. The side facing us is not illuminated, so the Moon is not visible or appears as a very faint outline.
Waxing Crescent 🌒
A small sliver of the Moon becomes visible as the illuminated portion increases ("waxing"). The crescent shape is on the right side in the Northern Hemisphere.
First Quarter 🌓
Half of the Moon appears illuminated. It's called "First Quarter" because the Moon has completed about one-quarter of its orbit since the New Moon.
Waxing Gibbous 🌔
More than half of the Moon is illuminated, and the illuminated portion continues to grow. "Gibbous" means more than half but less than full.
Full Moon 🌕
The Earth is between the Sun and the Moon. The entire face of the Moon visible from Earth is illuminated.
Waning Gibbous 🌖
After the Full Moon, the illuminated portion starts to decrease ("waning"). More than half is still illuminated.
Last Quarter 🌗
Half of the Moon is again illuminated, but it's the opposite half compared to the First Quarter. This marks about three-quarters of the way through the lunar cycle.
Waning Crescent 🌘
Only a small sliver remains illuminated as the Moon approaches the New Moon phase. The crescent is on the left side in the Northern Hemisphere.
Source information based on astronomical observations and educational resources from organizations like NASA and The Planetary Society. The cycle from one New Moon to the next (a synodic month) takes about 29.5 days.