Gazing at the stars

Dennis Overbye, a science writer and reporter, recently posted a fascinating article on the telescopes of Las Campanas Observatory located on a plateau high in the Chilean Andes in the Atacama desert. It is one of the driest and darkest places in the world and thus an ideal place for building very large telescopes with which to peer into the depths of the cosmos. How large? Some of the telescopes located at Las Campanas are the Very Large Telescope, composed of four telescopes, each more than eight meters (27 feet) in diameter. It was built by an international collaboration called the European Southern Observatory. The Vera C. Rubin Observatory, another eight-meter telescope, is set to start operating next year, mapping the entire sky every three days. Vera Rubin was the first astronomer to postulate the existence of “dark matter.”

Las Campanas will have newer, larger observatories in the near future. The Carnegie Institution is leading a consortium of 13 universities and institutions in the building of the Giant Magellan Telescope, or G.M.T., a multibillion-dollar instrument more powerful than any existing ground-based telescope. When completed, the telescope will have seven mirrors, each eight meters in diameter, that together will act as a 22-meter-diameter telescope. The possibilities for research are amazing. The design includes a sophisticated adaptive-optics system to compensate for atmospheric turbulence that can blur celestial details (and make stars twinkle). And some of the mirrors will be able to adjust their shape 2,000 times a second, to keep star images crisp over a field of view two-thirds the size of a full moon. (The Webb telescope’s field of view is only one-tenth of a full moon.)

Jonathan O’Callaghan notes that one of the fascinating elements of these developments is the way in which earth-based telescopes are able to accommodate and adjust for earth-based limitations – weather, humidity, wind, etc. But some astronomers think that there is an existential threat to their work because of the proliferation of earth-orbiting satellites such as Space X’s Starlink. U.S.-based SpaceX plans to launch at least 12,000 satellites, with the possibility of lofting another 30,000, based on recent filings from the company. U.K.-based OneWeb hopes to orbit about 650 satellites, possibly increasing to almost 2,000 in the future, and U.S.-based Amazon is planning for more than 3,000 satellites in its Project Kuiper constellation. Other companies and nations, including China, also have their eye on developing similar constellations, with rough estimates suggesting there could be more than 50,000 satellites in total added to Earth orbit in the coming decades. As low-Earth orbit fills with constellations of telecommunications satellites, astronomers are trying to figure out how to do their jobs when many cosmic objects will be all but obscured by the satellites’ glinting solar panels and radio bleeps.

Astronomers acknowledge that SpaceX has tried a variety of methods to darken its satellites, but the spacecraft are still visible, and other providers are not adopting any such mitigation strategies. What’s more, newer Starlink satellites and those made by other companies are much larger and brighter. A company called AST SpaceMobile launched a prototype last September—BlueWalker 3. Two months later, when BlueWalker 3 deployed its 693-square-foot (64.4- square-meter) phased array of antennas to allow communication with cell phones on Earth, it became one of the brightest objects in the night sky, outshining more than 99 percent of the stars visible to the naked eye.

AST SpaceMobile aims to launch 168 even larger satellites, called BlueBirds, in the next few years. A company spokesperson said testing of BlueWalker 3 will help engineers evaluate the satellite’s materials and judge its brightness, adding that the company is actively working with industry experts and NASA to mitigate brightness concerns. AST SpaceMobile is considering antireflective materials and changes to operations to make the satellites dimmer. There will be many fewer BlueBird satellites than other constellations, but they may pose a different type of problem. Some telescopes may be able to avoid very bright BlueBirds, the way some telescope cameras are designed to avoid bright objects such as the planets or the moon. But hundreds of them will be harder to escape. And a bright satellite passing through a digital camera’s long exposure could fry the camera’s sensitive electronics.

This is all part of a larger problem of space debris. At the moment the Depart of Defense is tracking over 23,000 objects (softball size and larger) that are orbiting earth. But that’s a topic for another day.

Image credit: Yuri Beletsky of Las Campanas Observatory
Sources: Dennis Overbye, New York Times and Jonathan O’Callaghan in Scientific America

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