The Moon’s Far Side

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    ID: 4253 Visualization

    Moon Phase and Libration, from the Other Side

    Feb. 4th, 2015
    (updated May 3rd, 2023)

    This narrated video introduces two views of the Moon's far side. Transcript.This video is also available on our YouTube channel. || A number of people who've seen the annual lunar phase and libration videos have asked what the other side of the Moon looks like, the side that can't be seen from the Earth. This video answers that question. (Update: The video was selected for the SIGGRAPH 2015 Computer Animation Festival.)Just like the near side, the far side goes through a complete cycle of phases. But the terrain of the far side is quite different. It lacks the large dark spots, called maria, that make up the familiar Man in the Moon on the near side. Instead, craters of all sizes crowd together over the entire far side. The far side is also home to one of the largest and oldest impact features in the solar system, the South Pole-Aitken basin, visible here as a slightly darker bruise covering the bottom third of the disk.The far side was first seen in a handful of grainy images returned by the Soviet Luna 3 probe, which swung around the Moon in October, 1959. Lunar Reconnaissance Orbiter was launched fifty years later, and since then it has returned hundreds of terabytes of data, allowing LRO scientists to create extremely detailed and accurate maps of the far side. Those maps were used to create the imagery seen here.In the first of the two viewpoints, the virtual camera is positioned along the Earth-Moon line at a distance of 30 Earth diameters from the Moon and 60 ED from the Earth. The focal length is equivalent to a 2000 mm telephoto lens on a 35 mm SLR, making the horizontal field of view about one degree. The view is consistent with what you might see through an amateur telescope at these distances.In the second view, the virtual camera is much closer to the Moon, only 1.2 ED, versus 31 ED from Earth. The camera focal length has been reduced to 80 mm, giving a 25° horizontal field. The result is an Earth that appears much smaller, more closely resembling the way it would look to the eye from the surface of the Moon. ||

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  • 
    ID: 4236 Visualization

    Moon Phase and Libration, 2015

    Dec. 9th, 2014
    (updated Aug. 25th, 2023)

    || Dial-A-Moon || New: Click on the image to download a high-resolution version with labels for craters near the terminator. The data in the table for the entire year can be downloaded as a JSON file or as a text file.The animation archived on this page shows the geocentric phase, libration, position angle of the axis, and apparent diameter of the Moon throughout the year 2015, at hourly intervals. Until the end of 2015, the initial Dial-A-Moon image will be the frame from this animation for the current hour.More in this series:Moon Phase and Libration GalleryLunar Reconnaissance Orbiter (LRO) has been in orbit around the Moon since the summer of 2009. Its laser altimeter (LOLA) and camera (LROC) are recording the rugged, airless lunar terrain in exceptional detail, making it possible to visualize the Moon with unprecedented fidelity. This is especially evident in the long shadows cast near the terminator, or day-night line. The pummeled, craggy landscape thrown into high relief at the terminator would be impossible to recreate in the computer without global terrain maps like those from LRO.The Moon always keeps the same face to us, but not exactly the same face. Because of the tilt and shape of its orbit, we see the Moon from slightly different angles over the course of a month. When a month is compressed into 24 seconds, as it is in this animation, our changing view of the Moon makes it look like it's wobbling. This wobble is called libration.The word comes from the Latin for "balance scale" (as does the name of the zodiac constellation Libra) and refers to the way such a scale tips up and down on alternating sides. The sub-Earth point gives the amount of libration in longitude and latitude. The sub-Earth point is also the apparent center of the Moon's disk and the location on the Moon where the Earth is directly overhead.The Moon is subject to other motions as well. It appears to roll back and forth around the sub-Earth point. The roll angle is given by the position angle of the axis, which is the angle of the Moon's north pole relative to celestial north. The Moon also approaches and recedes from us, appearing to grow and shrink. The two extremes, called perigee (near) and apogee (far), differ by more than 10%.The most noticed monthly variation in the Moon's appearance is the cycle of phases, caused by the changing angle of the Sun as the Moon orbits the Earth. The cycle begins with the waxing (growing) crescent Moon visible in the west just after sunset. By first quarter, the Moon is high in the sky at sunset and sets around midnight. The full Moon rises at sunset and is high in the sky at midnight. The third quarter Moon is often surprisingly conspicuous in the daylit western sky long after sunrise.Celestial north is up in these images, corresponding to the view from the northern hemisphere. The descriptions of the print resolution stills also assume a northern hemisphere orientation. (There is also a south-up version of this page.) ||

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  • 
    ID: 4109 Visualization

    Lunar Far Side: From Luna 3 to LRO

    Oct. 2nd, 2013
    (updated Aug. 25th, 2023)

    In October of 1959, the Luna 3 spacecraft launched from the Baikonur Cosmodrome in Kazakhstan. Luna 3 was the third spacecraft to reach the Moon and the first to send back pictures of the Moon's far side. The pictures were noisy and indistinct, but because the Moon always presents the same face to the Earth, they offered views of a part of the Moon that had never been seen before.The far side of the Moon is surprisingly different. The most striking difference evident in the Luna 3 pictures is the absence of the large, dark seas of cooled lava, called maria, that cover a substantial fraction of the Earth-facing near side. The far side is instead densely peppered with impact craters of every size and age.Fifty years later, in June of 2009, Lunar Reconnaissance Orbiter (LRO) launched from Kennedy Space Center in Florida. Using LRO's global elevation maps and photographic mosaics, both of which are of unprecedented quality and detail, it's possible to accurately recreate the view captured in the pictures from Luna 3. As seen here, Luna 3 was directly over 12°N 120°E at a distance of 61,700 kilometers above the surface, and its camera was banked 17.5° clockwise from vertical relative to the Moon's north pole.The thicker blue longitude line at 90°E, along the left side of the LRO image, marks the boundary between the near and far sides of the Moon. To the left of that line are the familiar maria Crisium (the circular spot near the 9 o'clock position), Marginis, Smythii (both east of Crisium), Humboldtianum (in the north), Australe (near the south pole), and the eastern edge of Fecunditatis. The bright spot near the center of the disk is a complex of unnamed craters bordered by King, Langemak, Gregory, and Abul Wafa craters. The brightness is enhanced because it's near the subsolar point. The dark, sharp-edged shield shape in the southern hemisphere, with the white dot in the middle, is Tsiolkovskiy crater and its central peak. The dark spot to the southeast of Tsiolkovskiy is the crater Jules Verne. The mare in the northeast is Moscoviense. ||

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