Commissioning of the Vera C. Rubin Observatory and Weak Gravitational Lensing

• Pierre-Francois Leget (Princeton/Harvard)

Room: 108/1-XX - Grande Salle 108 The Rubin Observatory began commissioning LSSTCam in April 2025, with the Legacy Survey of Space and Time (LSST) scheduled to start in 2026. Preliminary data collected through January 2026 will be publicly released as Data Preview 2 (DP2) in mid-2026. At the end of February 2026, the observatory reached a major milestone with the first public distribution of real-time alerts to community brokers. One of the primary science goals is to constrain Dark Energy through weak gravitational lensing — measuring how the shapes of distant galaxies are subtly distorted by the gravitational influence of matter along the line of sight. After just one year of data, these measurements are expected to reach a precision comparable to recent DESI results, providing an independent test of the intriguing hints that Dark Energy may evolve over time. However, weak lensing requires exquisite control of instrumental effects that can mimic or mask the cosmological signal. The first months of commissioning have shown that reaching this precision is a significant technical challenge. This seminar will present an overview of the Rubin Observatory commissioning — the successes achieved and the systematic issues we are working to resolve.