By Emily Levesque, University of Washington
On 21 April 1972, astronomy reached an exciting new milestone: Apollo 16 became the fifth mission to land on the moon. It, however, did something brand-new for astronomy: it operated the first, and so far, the only, telescope to observe from the surface of the moon. This telescope was the brilliant invention of a physicist and engineer named George Carruthers.
George Carruthers
Astronauts John Young and Charlie Duke’s work on the moon focused on exploring its geology and origins, and it built on previous exciting research that had also been carried out by past missions. Apollo 16’s telescope, built by George Carruthers, was exceptional as it was specifically designed to observe ultraviolet light.
Carruthers had been building telescopes since he was a child. He was born in Cincinnati in 1939, and by age 10 he had constructed a telescope out of cardboard tubing and lenses bought from a mail-order catalogue using the money he’d earned as a delivery boy.
At the University of Illinois, Carruthers earned a bachelor’s degree in aeronautical engineering and then went on to complete an aeronautical and astronautical engineering PhD in just three years.
Ultraviolet Camera and Spectrograph
Working at the Naval Research Laboratory, Carruthers was soon heading up a project to design an ultraviolet camera and spectrograph that could be taken to the moon. The key challenge that he and his team needed to tackle was designing a detector that specifically responded to ultraviolet light.
The technology used for optical astronomy, like light-sensitive glass plates or the imaging tube designed by Kent Ford that was ultimately used to study dark matter, wasn’t suitable for the ultraviolet range.
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Designing New Filters
First, the telescope needed to filter out non-ultraviolet light, which meant designing new filters that had never been needed on the ground. Second, the ultraviolet photons that made it through those filters needed to react with a light sensitive material.
The challenge was compounded by the fact that the same chemical compounds that reacted so nicely when exposed to visible light would have a very different response when exposed to higher-energy ultraviolet light.
First Ultraviolet Camera
Carruthers ultimately designed and patented the first ultraviolet camera. The camera passed light through plates made of lithium fluoride or calcium fluoride, compounds chosen because they allowed only very short wavelengths of light to pass through.
The light then struck a negatively charged electrode coated with potassium bromide, which would spit out electrons when struck by ultraviolet light. Those electrons were then focused onto a strip of film that would auto-advance after every exposure, surprisingly similar to classic film cameras.
The Apollo 16
Carruthers’s finished telescope, the Far Ultraviolet Camera and Spectrograph, was a small but powerful telescope with a three-inch mirror. The Apollo 16 crew carried it to the moon and set it up on the lunar soil using a tripod, situating it in the shadow of the lunar lander. Things didn’t quite go flawlessly for the little telescope, however.
During the mission John Young and Charlie Duke would occasionally get tangled in the cables connecting the telescope to its battery, and the battery itself struggled in the extreme temperatures of the lunar surface.
The lubricant that was supposed to make the telescope turn smoothly also started to gum up in the cold, leaving the astronauts struggling to wrestle the telescope into place.
Ultraviolet Astronomy Images
The telescope did its job, but for all its efforts the newly invented ultraviolet camera got left behind, exchanged for the weight of moon rocks. The astronauts flew home with just the lightweight canister of exposed film containing the world’s first ultraviolet astronomy images.
Carruthers and his colleagues were able to admire the stars and nebulae of our own Milky Way in a never-before-seen wavelength. The telescope’s observations also gave us another unique view, pointing back at our own planet to study Earth’s atmosphere and magnetic field.
Ultraviolet Astronomy Cameras
Carruthers continued his work in ultraviolet astronomy after the Apollo program ended. We could now send more telescopes into space, and a copy of the same camera he created for Apollo 16 flew on a Skylab mission in 1973.
Other ultraviolet astronomy cameras flew on board high-altitude balloons or suborbital rockets, traveling just high enough to leave Earth’s light-blocking atmosphere and capture new ultraviolet observations.
NASA’s Space Astronomy Program
Ultraviolet astronomy also enjoyed early successes in NASA’s fledgling space astronomy program. Nancy Roman, the same scientist who led the start of the Hubble Space Telescope, oversaw the launch of the Orbiting Astronomical Observatories in the late 1960s and early ’70s.
It carried several ultraviolet detectors and kicked off the era of ultraviolet satellite observations.
International Ultraviolet Explorer
In 1978, the International Ultraviolet Explorer, or IUE was launched as a joint collaboration between the United States, the UK, and the European Space Agency, a smashing success.
The IUE ultimately operated for 18 years and became the first space observatory that could be run in real time by astronomers working at operating stations on the ground.
Dedicated to ultraviolet astronomy, the IUE revolutionized astronomers’ understanding of the hottest and most massive stars, the hot gas churning around supermassive black holes, and even the diffuse dust of interstellar space that casts a shadow in the ultraviolet by blocking this short-wavelength light.
The IUE observed Venus, Halley’s comet, and even the 1987 supernova.
The Hubble Space Telescope
Today, the Hubble Space Telescope is the most prolific ultraviolet telescope, with two different cameras dedicated to capturing ultraviolet light. Many of the famous, and beautiful, Hubble photographs include ultraviolet data, corrected to blue or purple wavelengths. They carry valuable information that would be invisible without the advantages of being in orbit and the technology of cutting-edge ultraviolet detectors.
Hubble is an excellent example of a multi-wavelength telescope, observing ultraviolet, visible, and infrared light by combining its classic reflective mirrors with cameras and detectors that have been custom-designed for different wavelengths.
Common Questions about How George Carruthers Invented the Ultraviolet Astronomy Camera
George Carruthers constructed a telescope at the age of 10.
George Carruthers’s finished telescope, the Far Ultraviolet Camera and Spectrograph, was a small but powerful telescope with a three-inch mirror.
The International Ultraviolet Explorer ultimately operated for 18 years.
