There will be no readers’ wildlife today: I’m saving up the photos for when I’m in Poland. Instead, have a gander at this photo:
This still photo of the moon interposed between a satellite and Earth was going around yesterday, and some who saw it automatically cried “Photoshop!” (I don’t think I’ve ever posted an amazing photo that hasn’t aroused that cry.) Now, it’s okay to say, “I’m dubious,” but a proper skeptic should say, “I better investigate further.” And if you did, you’d see that this photo was genuine, as described by NASA.
First, a time-lapse taken from the NASA site. You’re seeing here what you never see from Earth: the “dark side” of the moon. The bit below tells you why we never see the moon’s bum, which you need to know:
Part of NASA’s explanation:
A NASA camera aboard the Deep Space Climate Observatory (DSCOVR) satellite captured a unique view of the moon as it moved in front of the sunlit side of Earth last month. The series of test images shows the fully illuminated “dark side” of the moon that is never visible from Earth.
The images were captured by NASA’s Earth Polychromatic Imaging Camera (EPIC), a four megapixel CCD camera and telescope on the DSCOVR satellite orbiting 1 million miles from Earth. From its position between the sun and Earth, DSCOVR conducts its primary mission of real-time solar wind monitoring for the National Oceanic and Atmospheric Administration (NOAA).
. . . A NASA camera aboard the Deep Space Climate Observatory (DSCOVR) satellite captured a unique view of the moon as it moved in front of the sunlit side of Earth last month. The series of test images shows the fully illuminated “dark side” of the moon that is never visible from Earth.
The far side of the moon was not seen until 1959 when the Soviet Luna 3 spacecraft returned the first images. Since then, several NASA missions have imaged the lunar far side in great detail. The same side of the moon always faces an earthbound observer because the moon is tidally locked to Earth. That means its orbital period is the same as its rotation around its axis.
I don’t fully understand “tidal locking,” but it has to do with the Earth’s huge mass acting to slow down the Moon’s originally faster rate of rotation, and with the gravitational pull of the Moon, which causes Earth’s tides. The slowing apparently stops when the rotational speeds of the Earth and Moon are identical. A physics maven might explain the phenomenon further in the comments. What is clear is that this locking is absolutely precise: over centuries the rate of the Moon’s rotation has exactly matched that of Earth’s—to the extent that even our distant forebears didn’t see the Moon’s bum.
Actually, we can see a bit more of the Moon’s hidden side, as it wobbles a bit on its axis, a phenomenon called lunar libration. This allows us to see, in toto, 59% of the Moon’s surface. And, of course, the “dark side of the Moon” isn’t really dark, for it’s illuminated by the sun when that side is between the Earth and the Sun. We just don’t see the “dark side” because of the precise locking of rotational speed.
h/t: Alan G