In short, “the dark side of the moon” is an invalid name error. Even though it sounds cool. But this is a mistake. If we assume that people are not talking about one of the albums of Pink Floyd, “dark side of the moon” refers to its far side — which, despite the fact that it is always looking from the Earth, does the same amount of sunlight, how much and staring at the Land side. Perhaps you already knew about it. But did you know that some regions of the secret side of the moon periodically seem to us? Or that some lunar regions are actually shrouded in eternal darkness?
Dark side of the moon is not actually dark
To understand why, you first need to understand why one side of the moon is directed away from Earth. For those who live on the Earth, natural satellite of our planet will never rotate. But in fact it rotates all the time — just its rotation around its axis and around the planet takes one speed: once every 27 days or so. When the outer body is rotated around its parent and its axis with the same speed, astronomers say that it is “tidal locked”.
Our Moon was not like this from birth. Astronomers believe that, like many other natural satellites, initially it rotates with a different speed. In the case of the Moon, when it rotates faster around its axis. But over time, the gravity of the planet can have a greater effect on the convexity of the lunar surface and forced to synchronize its rotation with the orbital period. This phenomenon is actually quite common: many moons of Saturn and Jupiter tidal associated with the parent planet.
Tidal locking — that’s why we didn’t know how does the far side of the moon until 1959, while the Soviet probe “Luna-3” did not do the first pictures are covered with craters landscape. Since then, we did some nice shots: in 1968, the astronauts of mission “Apollo-8” were the first people who saw the far side of the moon with my own eyes. Probe Lunar Reconnaissance Orbiter has made a complete map of the lunar surface at high resolution, starting in 2009. Just recently, China became the first country that conducted a soft landing of the spacecraft and deploy a Rover on the dark side of the moon.
But let’s be honest: we don’t need a spacecraft to see the far side of the moon. While you can see only 50% of the lunar disk at a particular point in time, stain the surface permanently ajar careful observer. In fact, the lunar cycle to 59% of the moon is visible to observers on the Ground — provided that they know what to look for.
Look at this visualization of NASA. It was made using satellite imagery from Lunar Reconnaissance Orbiter. Phase change with which you are no doubt familiar to reflect the offset provisions of the moon relative to the Sun and Earth. As the displacement of the moon, the darkness finds and moves away from the front side, which is tidal locked to our planet. This animation, which brings together two half lunar cycle in one 13-second GIF illustrates something about the moon, that maybe you haven’t noticed before: she swings.
Astronomers call these rocking of the library, and they are caused by the orientation of the axis of the moon and the elliptical shape of its orbit. The tilt of its axis relative to the Earth makes the moon look as though it slowly and gently bows, allowing observers to see her fleetingly North and South poles. Similarly, the eccentricity of the orbit of the moon makes its front part slightly trembling, allowing people to peer into its Eastern and Western edges that belong to the “dark side”.
The axial tilt of the moon leads to another interesting phenomenon: some portions of the lunar surface are in eternal darkness.
The image at the beginning of the article is the map lighting the moon’s South pole. This is a composite image, assembled from more than 1700 pictures obtained by the Lunar Reconnaissance Orbiter for six months. The field pole, which has not seen light in a while, look black; those that have seen the light, look white; gray is something in between. The black circle in the center of the image is the Shackleton crater, an impact crater is 20 km long with a rim, which is eternal casts a long shadow on its interior.
All of this suggests that “dark side of the moon” is not technically exist, but the “craters of eternal darkness” (okay, sounds even better) is definitely there.
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