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Planets and moons

Why can we sometimes see the Moon in the day?

Daytime Moon seen in ColoradoDaytime Moon seen in ColoradoWe think of the Moon as something we see only at night, or as the daylight dims in the evening. In fact, the Moon is visible during the day just as often as it is at night. The Moon produces no light of its own, but reflects the light from the Sun. The Sun’s rays bounce of its surface, giving it the brilliant white glow we see from Earth. Being so close to us, the Moon is the second brightest object in the sky—bright enough to be seen in daylight hours, while the Sun outshines the stars and planets. Provided the Moon is high enough in the sky, we are thus able to see it during the day.

The changing phases of the Moon, as seen from EarthThe changing phases of the Moon, as seen from EarthThe Earth, tilted on an axis, orbits around the Sun. At the same time, the Moon travels around the Earth, with one side of it permanently facing towards us. The Sun always shines on roughly half the Moon; it is this part we see from different angles as the Moon travels around the Earth. Sometimes none of the Moon's illuminated side is visible from Earth at all. This is called a New Moon.

As the Moon continues on its orbit round the Earth, more and more of its illuminated side becomes visible (the changing shapes are called lunar phases) until it appears as a complete, brilliant disc, known as a Full Moon: its illuminated side is fully visible from Earth. After that, less and less of the Moon's illuminated side is visible from day to day, until once again it becomes an invisible New Moon. From one New Moon to the next takes 29.5 days.

Full moon over Santorini, GreeceFull moon over Santorini, Greece  

A Full Moon is the only phase when the Moon shines at night and doesn't appear in the daytime sky.

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