Question

How much of the moon is illuminated by the sun at any given point of time?

Answer 1

Hint: A celestial body that orbits a planet or minor planet is called a natural satellite.The Moon is our Earth’s only natural satellite. Located at a distance of 3,85,000km away from, earth’s moon is the fifth largest moon of our solar system.

Complete answer: The Moon has an unbreathable thin atmosphere and rocky surface. Its surface has pits called craters.
The moon moderates earth’s wobble on its axis, stabilizes earth’s climate and its gravitational pull influences the tides in the oceans.
The moon rotates at the same rate as it revolves around the earth. This is known as synchronous rotation because of which the same side or hemisphere of moon faces the earth all the time. Half of the moon is illuminated by the Sun at any given point of time.The moon takes 27 earth days to orbit around earth. As the moon moves in its orbit around the earth, different parts of the moon receive sunlight because of which we see different phases of the moon like the full moon, crescent and new moon. On full moon day, the hemisphere of the moon that faces earth gets illuminated by the Sun. On a new moon day, the hemisphere or the side of the moon that we do not get to see from earth receives sun rays.
Though the moon takes 27 earth days to make one orbit around earth , the earth is moving on its axis and around the sun as well. This is why the moon appears to orbit us every 29 days. The 27 days period is called the sidereal period whereas the 29days period is called the synodic period.

Therefore the answer is that 50% of the moon's surface is always illuminated by the sun.

Note: There are various theories proposed to explain the formation of the moon. One of the leading theories is that the moon was formed when a mars sized object collided with earth.
Another fact to note is that it was Indian Mission Chandrayaan 1 which first made discovery of water on the moon.