Rubin's 8.4-meter Mirror Reaches the Summit

This morning, a unique astronomical mirror reached its new home in the Andes Mountains of Northern Chile. This incredible mirror will enable the Large Synoptic Survey Telescope (LSST) to catalog an estimated ~40 billion celestial objects—more objects than there are humans on earth. LSST will scan the entire visible sky every few nights, visiting each location approximately ~1000 times during its ten-year survey, which is scheduled to begin in 2022. With these fast, repeated observations LSST will open a new window to the changing Universe, providing countless new opportunities to do science with transient objects such as asteroids and supernovae. Additionally, with the wide field of view made possible by this mirror, LSST will advance the study of dark matter and dark energy. The 8.4-meter LSST Primary/Tertiary Mirror (M1M3), one of the largest and most recognizable elements of the telescope, is unusual because it consists of two mirror surfaces combined on one large substrate. Light from the sky will hit the outer ring (M1) first, reflect upwards to a separate second mirror (M2), and then bounce back down to the inner ring (M3) of the monolith before reaching the telescope. LSST's three-mirror design, combined with a highly sensitive camera, allows the telescope to collect light from faint objects over a very large field of view. Combining the M1 and M3 mirrors gives the telescope a more compact shape, which enables it to move (slew) quickly between points on the sky and to settle efficiently before taking its next image. The M1M3 safely arrived at the LSST summit facility building on Cerro Pachón in Chile on May 11, 2019. Its eight-week journey began on March 15, in Tucson, Arizona, USA, where it was fabricated. The M1M3 was the first LSST component to be completed, and the mirror will play a critical role in enabling countless scientific discoveries.