This Friday night, I observed the moon. It was almost 100% full. It was the biggest one of the year as it reaches its closest point to our planet. Full moon is a lunar phase that occurs when the Moon is on the opposite side of the Earth from the Sun. In the language of Astronomy, a full moon occurs when the geocentric apparent longitudes of the Sun and Moon differ by 180 degrees; the Moon is then in opposition with the Sun. The Moon is the Earth’s only natural satellite and the fifth largest natural satellite in the Solar System. The center-to-center distance from the Earth to the Moon is 384,403 km. Moon’s volume is about 2 percent that of Earth and the pull of gravity at its surface about 17 percent that of the Earth. The Moon makes a complete orbit around the Earth every 27.3 days (the orbital period), and the periodic variations in the geometry of the Earth-Moon-Sun system are responsible for the lunar phases that repeat every 29.5 days.

The Moon is the only celestial body to which humans have traveled and upon which humans have landed. The first artificial object to escape Earth’s gravity and pass near the Moon was the Soviet Union’s Luna 1, the first artificial object to impact the lunar surface was Luna 2, and the first photographs of the normally occluded far side of the Moon were made by Luna 3, all in 1959. The first spacecraft to perform a successful lunar soft landing was Luna 9, and the first unmanned vehicle to orbit the Moon was Luna 10, in 1966. This year, India has also launched its first satellite to moon. It is known as Chandrayaan-1. It is India’s first mission to the moon launched by India’s national space agency the Indian Space Research Organization (ISRO). The unmanned lunar exploration mission includes a lunar orbiter and an impactor.