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Hubble and Gaia Team Up to Fuel Cosmic Conundrum

Using the powerful Hubble and Gaia space telescopes, astronomers just took a big step toward finding the answer to the Hubble constant, one of the most important and long-sought numbers in all of cosmology. This number measures the rate at which the universe is expanding since the big bang, 13.8 billion years ago. The constant is named for astronomer Edwin Hubble, who nearly a century ago discovered that the universe was uniformly expanding in all directions. Now, researchers have calculated this number with unprecedented accuracy.

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Announcement Notice

NASA and The Space Telescope Science Institute (STScI) are pleased to announce the Cycle 26 Call for Proposals for Hubble Space Telescope (HST) Observations and funding for Archival Research and Theoretical Research programs. Participation in this program is open to all categories of organizations, both domestic and foreign, including educational institutions, profit and nonprofit organizations, NASA Centers, and other Government agencies.

Cycle 26 will extend from October 1, 2018 to September 30, 2019. We will accept proposals for the following instruments: ACS, COS, FGS, STIS, and WFC3.

This solicitation for proposals will be open through August 17, 2018 8:00pm EDT. The Astronomer's Proposal Tools (APT), which is required for Phase I Proposal Submission will be released for Cycle 26 Phase I use on May 14, 2018. Results of the selection will be announced by the end of October 2018

Please see the Cycle 26 Announcement page for detailed information.

Please take note of the What's New for Cycle 26 section on the announcement page. In particular, the Director has decided to implement an anonymous review process for Cycle 26. This follows recommendations by a working group and discussion with the Space Telescope Users Committee (presentation).The decision has been endorsed by the STUC, the Space Telescope Institute Council and the AURA Board, and is supported by NASA. A description of the process and instructions on how to adjust proposals to comply with the new requirements are included in the Call for Proposals.

Questions can be addressed to the STScI Help Desk (web:, email: or phone: 410-338-1082).

Fundamental Physics with HST

Over the last three decades the Hubble Space Telescope has played a crucial role in probing key parameters relevant to fundamental physics and cosmology. The H(0) key project figured prominently in during the early years, and subsequent programs have reduced measurement uncertainties to less than 3%. More recently, Hubble has investigated other parameters, including testing the nature of dark matter through observations of merging galaxy clusters and using white dwarf spectra to constrain the gravity dependence of the fine structure constant.

Looking forward, the STScI Director convened a working group drawn from the physics and cosmology communities to provide advice on how Hubble might contribute to future investigations in fundamental physics. The committee was chaired by Prof. Bhuvnesh Jain (University of Pennsylvania), and included Prof. Neal Dalal (University of Illinois), Professor Cora Dvorkin (Harvard University), Prof. Jeremy Heyl (University of British Columbia), Prof. Marc Kamionkowski (Johns Hopkins University), Dr. Phil Marshall (SLAC National Accelerator Laboratory), and Prof. David Weinberg (Ohio State University). The committee consulted with members of the community and submitted a final report in November 2017.

The Charter can be found here as well as the Final Report.

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Hubble Legacy Archive

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