Euclid Publishes 900 Million Galaxies From 13 Months of Sky

The European Space Agency released catalogues and images covering more than 900 million galaxies on 12 November 2026, the first major batch of data from its Euclid space telescope. The release, named DR1-Foundation, draws on about 13 months of observations and spans 1,900 square degrees of sky, an area ESA describes as the size of 9,500 full Moons.

Alongside the galaxies, ESA says the release holds around 15,000 strong gravitational lensing candidates, more than 60 million quasar candidates and spectra from more than 160 million sources. It runs to roughly 1.7 petabytes and rests on about 10,000 science images from Euclid's two instruments: the visible-light camera VIS and the Near-Infrared Spectrometer and Photometer. The Euclid Consortium said on the same day that 24 technical papers describing the telescope and its processing, plus eight science analysis papers, went up on arXiv.

Thirty times the first taste

Euclid's first quick release, on 19 March 2025, covered 63 square degrees and represented a few days of observations. DR1-Foundation is about thirty times that area. It is still a fraction of the mission's ambition: the Euclid Wide Survey is planned to reach at least 14,000 square degrees, close to a third of the whole sky, across six years.

What the lenses are for

A DR1 catalogue paper led by Natalie Lines, a PhD student at the University of Portsmouth, reports 15,072 high-confidence strong lens candidates across the released area: 6,073 graded as sure lenses and 8,999 as probable ones. The paper notes that this single survey's high-confidence sample exceeds the total number of strong lenses discovered to date. Strong lensing matters here because it lets astronomers weigh individual galaxies including their invisible dark matter, which is the slower route to the same question Euclid's main survey asks.

The cosmology is not in this release

What DR1-Foundation does not contain is the measurement Euclid was built to make. The shear products that encode weak gravitational lensing, along with galaxy clustering statistics and galaxy cluster catalogues, are held back for the full Data Release 1 in mid-2027. Without them there is no official Euclid result on dark energy or dark matter, and the classifications in the published catalogues are provisional pipeline output rather than confirmed identifications. The validation campaigns needed to control systematic errors at the per cent level are still running.

Mat Page of UCL's Mullard Space Science Laboratory, who leads the VIS instrument, said the images "are amazingly sharp, and with images covering nearly 2,000 square degrees this data release is a gold mine for astronomical discovery". The honest reading is that this is an instrument and pipeline validation release presented as a discovery release, and that is not a complaint. Proving the camera and the processing chain over 1,900 square degrees is the harder half of the work, and it is the half that decides whether the 2027 cosmology is believable.

How many of the 15,000 lens candidates survive follow-up is not yet known. The largest planned spectroscopic programme, 4SLSLS, begins in late 2026 and will measure deflector and source redshift pairs for 10,000 lenses, which is what will eventually fix the true positive rate for the graded samples.