Every year, NASA releases a detailed simulation of the Moon that shows how it will change through the year. They produce a couple of versions that show how it appears from the northern and southern hemisphere and others that highlight different features. Not only does it show the phases through the year but it also shows the change in size as its completes its orbit. The change in apparent size of the Moon is a result of its elliptical orbit so that it can appear up to 30% brighter.
The Moon is Earth’s only permanent natural satellite. It has captivated humans for thousands of as it orbits at an average distance of 384,400 kilometres. It plays a key role in shaping our tides through its gravitational pull. The lunar surface is a desolate, rocky world with colossal mountains, and plains known as maria. It has no atmosphere and so experiences extreme temperature shifts, from intense solar heating in the day to freezing cold at night. Over the centuries, it has inspired countless myths and driven exploration that has culminated in the Apollo missions and soon Artemis.
One of the most well known aspects of the Moon are the lunar phases. The phases of the Moon represent its motion around the Earth and its changing appearance when viewed from Earth. The cycle lasts about 29.5 days and is known as a lunar month. It begins with a new moon when the Moon lies approximately between Earth and the Sun and appears nearly invisible as we look at the night time hemisphere.
As the cycle continues the crescent appears, getting larger and larger marking the waxing crescent phase. Eventually it leads to a first quarter phase when half of the Moon appears illuminated. It increases through the waxing gibbous phase before reaching full moon. The cycle then reverses through the waning phases to new moon again.
The phases appear nicely in the video from NASA but what is also apparent is the gentle rocking of the Moon. Known as libration, it means we get to see slightly more than 50% of the lunar surface, 59% over time. The phenomenon occurs due to the axial tilt of the Moon and its elliptical orbit. It can be categorised as three different types; longitudinal (caused by changes in Moon’s orbital speed,) latitudinal (caused by tilt in the Moon’s axis) and diurnal (caused by Earth’s rotation and a slight shift in position of observer.)
The video simulation produced by NASA has been created from images taken by the Lunar Reconnaissance Orbiter (LRO.) It has been in orbit since the summer of 2009 and has produced images of unprecedented quality. Using advanced instruments, it has mapped the surface in high detail, revealing detailed topography, temperature, and geological maps. It has identified landing sites, especially near the poles, where water ice may exist, and has captured images of some of the Apollo landing sites.
The animation shows the phases, and libration at hourly intervals until the end of 2025. One month is compressed down into about 24 seconds to give a comprehensive view of the year ahead.
Source : NASA Moon Animation