Remember the Chinese Chang’e 3 mission to the moon in December 2013? Once alighting on the dusty surface on December 14, the golf cart-sized Yutu rover wheeled down the lander’s ramp to photograph the landscape, measure the soil composition and probe the lunar crust with ground-penetrating radar. Everything went well until a mechanical malfunction stopped the rover in its tracks about a month later and prevented its solar cell panels from closing to keep the rover’s interior insulated from the extreme cold of the long lunar night. Despite these obstacles, Yutu’s instruments kept plugging away for a year until radio transmissions ceased this past winter.
Watch the dramatic landing of Chang’e 3 in HD
Meanwhile, one of the primary instruments on the lander, a camera that can take pictures of the sky in ultraviolet light, is still cranking out photos to this day. Called the Lunar-based ultraviolet telescope or LUT, its optics are specialized for UV light. Why ultraviolet and not visible light? Most UV lights gets blocked by Earth’s atmosphere, but not on the moon, where its next-to-nothing atmosphere allows ultraviolet light to pass straight down to the surface.
No atmosphere also means no blurring from atmospheric turbulence. Stars beam a steady light without twinkling as seen from the moon. One other big plus results from the moon’s very slow rotation. Since it takes 27 days to spin once, nights are 27 times as long. As the stars creep 27 slower across the sky, the telescope can remain focused on the same object for days.
The LUT features a light-gathering mirror just 5.9 inches (150 mm) across, but that’s big enough to capture stars down to 13th magnitude. As detailed in a recent paper, the scope’s been taking about 10,000 images per month over the past 18 months and studying variables or stars that vary in brightness over days and months – sometimes hours! Unfortunately, I could only track down one photograph despite the volumes that must exist. It shows a large galaxy in the Big Dipper nicknamed the “Pinwheel”. UV light is especially good at picking up the light given off by hot, young stars and star-forming regions, seen as bright blobs outlining the galaxy’s spiral arms.
China’s may be the first robotic scope on the moon, but the Apollo 16 astronauts set up a 3-inch (7.6 cm) Far Ultraviolet Camera-Spectrograph telescope on the lunar regolith way back in April 1972 and took photos and spectra of the Earth and aurora, star clusters and one of the nearest galaxies, the Large Magellanic Cloud. Their haul came to 178 photo on a film cartridge which was returned to Earth for analysis. The images would be the subject of many research papers for years to come.
While I understand the scientific importance of getting UV images of the night sky, if I could go to the moon, I’d bring a portable reflecting telescope like the one I use here at home. Without the jittery and often soft images caused by atmospheric turbulence, I could use my highest magnification to get rock-steady, crisp images of everything. Astronomical nirvana!
Coming back to the Chang’e 3 scope, Chinese mission control has to stow the telescope back inside the lander at each lunar sunrise and sunset due to abrasive dust thought to be aloft during those hours. The team is hoping to continue the mission past the end of the year.