The word 'perigee' is correct and usable in written English.
It is a noun that describes the point in the orbit of the moon (or other celestial body) when it is nearest to the earth. Example sentence: The moon was closest to the Earth at its perigee.
The Moon is typically about 12 percent (or about 43,000 km [27,000 miles]) closer to Earth at perigee than at apogee, and thus a full moon at perigee would be about 25 percent brighter than one at apogee.
However, supermoon came to denote the more-restrictive meaning of a full moon at perigee.
The reason for the advance of the perigee lies in the perturbing attraction of the Sun on the Moon, but Newton obtained a rate too small by half (a complete revolution of the perigee takes about 18 years instead of the observed 9).
Clairaut later withdrew this proposal and showed in a new calculation that the inverse-square law was perfectly adequate for explaining the motion of the Moon's perigee.
The satellite orbits Earth every 48 hours and is in an eccentric orbit (perigee of 7,000 km [4,000 miles] and apogee of 114,000 km [71,000 miles]) that allows long observations of astronomical objects.
In one anomalistic month, the Moon describes its orbit from perigee to perigee, the point at which it is nearest to Earth.
The astronomical term for this phenomenon is perigee-syzygy Moon.
At such times, the Moon appears at its largest and I accept it is easier to talk of a supermoon than to use the technically accurate phrase of "a perigee-syzygy of the Earth-Moon-Sun system".
Second, Newton had been unable to calculate the correct rate for the advance of the Moon's perigee that is, the movement of the point on the Moon's orbit where it is closest to Earth.
(The Moon moves most quickly when it is at perigee that is, when it passes closest to Earth).
For example, in the last three decades of the 20th century, the Moon's apogee the farthest distance that it travels from Earth in a revolution ranged between about 404,000 and 406,700 km (251,000 and 252,700 miles), while its perigee the closest that it comes to Earth ranged between about 356,500 and 370,400 km (221,500 and 230,200 miles).
