US astronomers might have only one huge ground-based telescope in their future, rather than the two that many had hoped for.

They have been planning for years to build the Giant Magellan Telescope on a mountaintop in Chile, and the Thirty Meter Telescope on the Hawaiian mountain Maunakea. Construction has started in Chile, while the Thirty Meter project has been building telescope components and doing other off-site work owing to concerns from Native Hawaiians over Maunakea, which they consider sacred. Both projects are backed by international groups of funders, but neither has the estimated US$3 billion needed to fully fund its telescope.

Many astronomers had hoped that the US National Science Foundation (NSF) would contribute money to cover the funding shortfall. But last week the National Science Board, which oversees the NSF, recommended that the agency cap its giant-telescope contributions at $1.6 billion. The board also signalled that it was reluctant for the NSF to spend even that much, citing the need to build other facilities “across a wide range of science and engineering fields”.

Taken together, the board’s actions suggest that the NSF will probably have to choose which of the two telescopes to fund — there might not be enough money for both. The agency is supposed to draw up a plan by May on how to decide which of the two to support.

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