Andy Garcia · freelance dev
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Euclid Is Set to Release About 1,900 Square Degrees on November 12. Galaxy Shapes Wait for Mid-2027

October 20, 2026 7 min read

ESA's Euclid space telescope is scheduled to deliver its first large public data release on November 12, 2026. It will not yet include the weak lensing and galaxy clustering products that Euclid's dark energy science rests on. On June 15, ESA announced that Data Release 1 would "proceed in two stages." The first, called DR1-Foundation, is to hold all raw data and calibrated images, catalogues and spectra over about 1,900 square degrees of sky. The complete DR1, "including the higher-level science products for galaxy clustering and weak lensing studies," is to follow in mid-2027.

Two caveats on the date. ESA's timeline page lists November 12 but warns that "data release dates are tentative and will have to be confirmed." And some older pages, including an October 8, 2025 news item from NASA's Euclid science center at IPAC, still give October 21, 2026, a date ESA's own timeline no longer shows. The most recent primary document I found, a content memo approved by the Euclid Science Team on September 22, states November 12.

I am not an astronomer. I ship software: a LegalTech built on Claude, where I am CTO, iOS apps, and a strategy game, Doomsday: M.A.D. What goes out now and what waits is a call every release forces. So I went past the announcement and read the memo, reference EUCL-EST-ME-8-020, and the archive's list of data products it points to. The split is more precise, and more instructive, than "some data now, the rest later."

What is scheduled for November 12

The Wide Survey part covers observations from the start of the survey, February 14, 2024, to May 21, 2025: roughly 500 square degrees in the northern hemisphere and 1,400 in the southern. The raw frames (Level 1, or LE1) reach further back: by default, all complete raw data generated since launch, on July 1, 2023, through May 21, 2025, minus some anomaly investigations, the invalidated data described below and incomplete survey data. Deep fields, calibration observations and some commissioning data are included too.

For scale: Euclid's first quick release, on March 19, 2025, covered 63 square degrees. DR1-Foundation is about 30 times that. The Wide Survey is planned to cover at least 14,000 square degrees, so this is under a seventh of it.

The calibrated layer (Level 2, or LE2) is substantial. From the product list: single-exposure and stacked images from both instruments, the visible camera VIS and the near-infrared NISP; merged mosaics and catalogues; photometric redshift catalogues; spectra and a spectroscopic catalogue; and a catalogue of detected strong gravitational lenses. The calibration products used to process all of it are to ship as well.

ESA also built in margin. Its coverage page marks about 2,100 square degrees for DR1 processing and expects about 1,900 to make it, because "inclusion in DR1 is not guaranteed for all blue-marked areas, as issues with the data may arise during the processing."

What waits for mid-2027

The memo is exact. DR1-Foundation includes everything in section 3 of the product list "except all products in sub-section 3.2.7." Sub-section 3.2.7 is SHE: six shear products built around two galaxy shape measurement methods, LensMC and MetaCal. Section 4, titled "LE3 products planned for full DR1," holds the rest, among them weak lensing correlation functions and power spectra, galaxy clustering statistics and galaxy cluster products.

Why shapes? Weak gravitational lensing is one of Euclid's two core cosmology probes (the other is galaxy clustering), and the way it traces invisible dark matter. Mass between us and a distant galaxy bends its light and stretches its image very slightly. You cannot see that in one galaxy, because you do not know its true shape. Giuseppe Congedo of the University of Edinburgh, who leads LensMC's development, put it this way in a Euclid Consortium article: "we measure the shapes of thousands of galaxies," and the distortions show up "as local net alignments in the ellipticities of galaxies."

That measurement is demanding. A telescope smears every point of light into a small pattern, its point spread function, and that smear also changes galaxy shapes, so it has to be modelled and removed. The memo notes that the calibration data for modelling the visible camera's point spread function had to be taken in thermal conditions stable "way beyond what is required for standard wide survey observations." Distances come from photometric redshifts, which, the memo says, need ground-based data to stay "within requirements for the weak lensing probe." And in a 2026 pilot study of one galaxy cluster, Abell 2390, a Euclid Consortium team repeated the full analysis with three independent shape algorithms and folded in calibrations from simulated data.

ESA's stated reason for the split is shorter: "additional time is needed to process and validate the higher-level science products across this large survey area." It does not say which step takes longer, and it does not report a problem. I would not read one in. For context, that Euclid Consortium article, published on June 5, ten days before the split was announced, already placed the first cosmology results in 2027.

The rules that make the first stage usable

A few lines in the memo matter more to me than the date.

No second pass. "There will be no reprocessing of products delivered at DR1-Foundation." What ships in November will not be redone when the complete DR1 follows. A researcher can build on it without waiting for a replacement within DR1.

Completeness is defined. Wide Survey observations without a ground-based counterpart, or taken while one instrument was not working, count as incomplete and are left out.

Bad data is named. Ice built up on Euclid's optics after launch: water absorbed on Earth, ESA explained in March 2024, was slowly released in space and froze onto mirrors in layers likely a few to a few tens of nanometres thick. Data taken between two decontamination campaigns, from March 23 to June 7, 2024, "were so far declared invalid" and left for a future delivery. To recover that area, DR1 includes re-observations covering what was observed from March 23 to May 21, 2024.

Limits are admitted. A change recorded in the memo's log excludes pointings that straddle the 0h line of right ascension (the sky's equivalent of longitude), the seam where it wraps from 24 hours back to zero, because "the current pipeline is not able to process data straddling" it. Anyone who has fought a wrap-around bug at midnight or at the date line will recognize the shape of that sentence. (That is an analogy; the memo does not describe the cause.)

And who decides when a problem turns up late is written down: before the internal data release, the science ground segment validates the data; if an issue is found after it, the ground segment raises a change request, the Science Team can recommend, and the Project Scientist decides.

What I take from it

A data release is not a software release, and one memo is not a case study. But the pattern transfers to anyone who ships a product in layers: a data platform, an API with analytics on top, a game with a content roadmap.

  1. Split along the validation burden. ESA says the higher-level science products need more time to process and validate, and the memo holds the shape catalogues, which feed the cosmology, back with them. Raw data, images and the other catalogues are scheduled first.
  2. Make the first stage final. A partial release you plan to quietly replace is a beta. One you freeze is a foundation. In software terms (an analogy again), it is a stable data contract that later features can depend on.
  3. Publish exclusions with their reasons: incomplete, invalid, not yet supported. A user who knows why something is missing can plan around it.
  4. Process more than you promise. About 2,100 square degrees in, about 1,900 expected out, said in advance.
  5. Ship something useful on its own. An ESA Datalabs hackathon is scheduled at ESA's European Space Astronomy Centre in Madrid from November 23 to 26 to hunt for rare objects in the new release: unusual galaxies, strong lenses, edge-on protoplanetary disks. That work needs images and catalogues, not cosmology statistics.

What the evidence does not show: whether mid-2027 will hold, whether the split delays any cosmology result, or whether November 12 itself will move. ESA calls the date tentative. I would check the timeline page before trusting the calendar.

Euclid is shipping its foundation first, and saying exactly what it is not. That is the part worth copying.

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