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OUR only record of how starry nights have changed over the past century is in
danger of vanishing. Astronomers are warning that most old photographs of the
night sky are disintegrating, and an urgent programme to store them in
electronic form is needed.

Today, state-of-the-art telescopes record vast amounts of data digitally on
computer servers. But until the 1990s, most observations were recorded on
photographic plates and so are not available in digital form. The world’s
astronomical archives contain more than 2 million photographic plates, some more
than a century old.

They hold our only information about how stars and galaxies vary in
brightness over several decades. “The information is unique, because the sky 100
years ago was not the same as it is today,” says Noah Brosch, director of Tel
Aviv University’s Wise Observatory in Israel.

Brosch says the plates could provide vital information about Pluto’s orbit
for future space missions to the tiny planet. They can also shed light on types
of astronomical objects only discovered in modern times. Archived plates have
revealed a visible flash that could have accompanied an “antique” gamma-ray
burst in 1905.

But young astronomers almost never consult these old photos. “They’re just
not trendy,” Brosch says. “We’re living in a digital age.” Due to the lack of
demand, many plates have been mothballed in inaccessible storage sites.

What’s more, many of the photos are disintegrating. These include plates
produced during the Carte du Ciel project, started in 1887, in which more than a
dozen observatories joined forces to photograph the entire sky. The photographic
emulsion on these plates is starting to crumble off the glass substrate. “How
would you feel if the Mona Lisa was to peel off and crumble in front of your
eyes?” says Brosch.

He and his colleagues are calling for an international effort to collect the
plates and record their information using electronic scanners. The Royal
Observatory of Belgium in Brussels has volunteered to hold the plates, but no
one has yet agreed to fund the project. Brosch hopes the European Union will
provide the money.

British astronomer Patrick Moore, presenter of the BBC’s TV programme The
Sky at Night, passionately backs the cause. “It’s essential to preserve
these plates, and people have to know where they are,” he says. He especially
mourns the removal of 90,000 plates from the Royal Greenwich Observatory in
Cambridge following the observatory’s closure in 1998. “The priceless plate
library is now stored in boxes somewhere—it’s vandalism.”