Now that Hallowe’en is out of the way, and we’re into November, the next scheduled break is in seven weeks time, for Christmas. The mid-term break fell in such a way that the 12 weeks of teaching split 5-7 instead of the tidier 6-6, which means that we have quite a long run-in. Lectures finish on Friday 18th December 2026. I don’t have any lectures on that day, actually, nor on the day before. I do have a tutorial on Friday 18th but I don’t imagine many students will turn up. I think I’ll try to get through the material before the end of term and then postpone the tutorial until the week before the examinations, which start on 8th January. That way I can spend a bit of time with a certain person before he goes to spend Christmas with his family.
Talking of examinations, I was a bit late getting my Semester 1 papers written but when I finally uploaded them I discovered that at least I wasn’t the last member of staff to complete this task. Every year the deadline for examination papers is pushed earlier and earlier. I don’t know why. Perhaps the people in charge just enjoy bossing the academic staff around.
I’ll be back to the office tomorrow to resume teaching, etc. but it is looking increasingly likely that we will be having more industrial action, as the negotiations between Unions and Government seem to have broken down. I know from talking to colleagues that there was considerable scepticism that the Government side were going to negotiate in good faith. The Minister’s comments to the media certainly don’t suggest that is the case. Anyway, we’re ready to go on strike again if necessary. I think November 1112th is the likely date for another 24-hour stoppage (updated from 11th). I have a medical appointment booked for that day, which will be cancelled if the strike goes ahead but it is routine and can be rescheduled. And if a one-day strike doesn’t work, who knows?
Among the highlights of the next seven weeks will be Euclid DR1 day on which will be published raw data, calibrated images, catalogues, and spectra covering approximately 1,900 square degrees. There won’t be any cosmology results – for those you will have to wait until mid-2027 – but the data set will be a feast in itself and is sure to attract considerable media attention.
I’m also thinking about preparing the Open Journal of Astrophysics for 2027. That will not only mean starting a new volume – Volume 10 – but also bringing in some changes to improve the workflow and improve the visual appearance of our published papers. We’re also going to publish a new policy on the use of AI in our papers. I suspect all journals are experiencing a deluge of AI-generated articles and OJAp is no exception. It’s very tiresome having to deal with all the slop, but it’s not going to go away anytime soon so we’ll just have to deal with it.
P.S. Today is Dia de Todos los Santos in Spain, a day on which people remember deceased family members and friends. The date takes on an especially sad significance this year after the terrible loss of life in a train crash last week.
The European Space Agency’s Euclid Mission is mapping the distribution of galaxies on large scales with the intention of finding out about the nature of dark matter and dark energy. Making such maps involves surveying large areas of the sky for a very long time and doing that makes it inevitable that something unexpected will crop up. That happened last month, between 16th and 24th September 2026, when the Euclid telescope accidentally discovered a comet.
Here is an image showing what Euclid was looking at when the comet intruded:
Here is is a comparison of frames showing the motion of the comet, which is easily identifiable by the large arrow pointing at it together with the word “comet”.
Picture Credit: ESA/Euclid/Euclid Consortium/NASA, M. Pöntinen et al. 2026
The serendipitous comet is named C/2026 S1 (Euclid) – and, before you ask, no it’s not an alien spacecraft.
Today, October 16th, is Hamilton day! It was on this day 183 years ago, in 1843, that William Rowan Hamilton first wrote down the fundamental result of quaternions. Apparently he was walking from his residence at Dunsink Observatory into Dublin when he had a sudden flash of inspiration, and wrote the result down on the spot, now marked by a plaque:
Picture Credit: Brian Dolan
This event is commemorated by an annual Hamilton Walk. Broombridge railway station (Droichead Broome), near the bridge (Broom Bridge), where Hamilton had his Eureka moment, is not far from Maynooth University the main commuter line from Maynooth into Dublin. This is ironic because Quaternion algebra does not commute. (Geddit?)
You may be interested that quaternions form the core mathematical framework used in the Euclid satellite’s telemetry system to represent and control its attitude (pointing direction and orientation). I also make extensive use of quaternions in preparing my tax return.
Although it is quite easy to reach Broombridge from Maynooth, I have never managed to attend the walk nor any of the other celebratory events because I’ve either been away or teaching. Perhaps one of these years, after I’ve retired, I’ll be able join the walk or attend one of the various ectures.
P.S. Maynooth University is also home to the Hamilton Institute which promotes and facilitates research links between mathematics and other fields.
I did a post a few months ago about Space Warps, a new citizen science project on the Zooniverse platform, in which volunters can search to find rare and elusive strong gravitational lenses in never-before-seen images captured by the European Space Agency’s Euclid space telescope. The project aims at shining a light on dark matter in galaxies and providing clues about the mysterious thing call dark energy.
The Space Warps Euclid project is entering the closing stages, but there is still about a week in which you can help with refining the final sample. Read more about it here:
Just a quick note to mention that tomorrow sees the launch of NASA’s Nancy Grace Roman Space Telescope. This is a survey telescope in some respects like ESA’s Euclid but with a larger aperture and different instrumentation, particularly a coronagraph which can block starlight to directly image exoplanets and planet-forming disks. Its larger mirror (2.4m versus 1.2m) will enable it to see fainter objects than Euclid, but its survey will be a much smaller fraction of the sky so in its cosmological applications it is complementary to Euclid rather than a direct competitor for it.
NASA have produced this sort of “cheat sheet” comparing the two observatories:
The Launch is due tomorrow (August 30 2026), at 7:26 am EDT which is 12.26 local Irish Time (same as BST). If you’re so inclined you can watch the launch on YooToob here:
Update: all seems to be well, and the Nancy Grace Roman Space Telescope is now on its way to L2.
The largest and most detailed photo ever made of the Galactic Centre in visible light was taken by the Euclid mission. For just one day (23rd March 2025), Euclid turned its gaze towards the extremely bright inner region of our Milky Way galaxy, known as the galactic bulge. The extraordinary picture that resulted is not part of Euclid’s main cosmological survey, which is designed to look at objects far outside our own Galaxy, but was made in response to a special request from astronomers who were after what Euclid does best: capturing large areas of the sky in crisp detail. Packed with more than 60 million stars, this image opens the door for scientists to confirm the existence of any exoplanet found in this region and measure its mass using tiny changes in starlight over time. The observational data obtained in this project were released today as Euclid’s Q2 data release; for details of Q1 please see here.
Designed to observe billions of faraway galaxies, the space telescope’s visible light camera is sensitive enough to tell apart individual stars in our super-crowded galactic bulge, without being blinded. This ability is crucial for what scientists want to use this image for: studying planets around other stars using a special technique called gravitational microlensing.
For comparison, Euclid’s sharpness and sensitivity in visible light is similar to the NASA/ESA Hubble Space Telescope’s wide field camera. But each pointing that Euclid captures in a few hours spans an area 270 times larger than Hubble’s field of view. To observe the same Euclid mosaic, the Keck Observatory would need around 2000 hours. Euclid is faster, and able to capture details from fainter stars that would be otherwise missed when observing from the ground. This single mosaic also encompasses the entire region that the upcoming Roman space telescope will monitor for planet hunting.
In a post last week I hinted that I hoped soon to be able to provide an update on progress with the European Space Agency’s Euclid Mission. People within the Euclid Consortium have known for some time, but it has now been officially announced by ESA, that the timeline for the first full Data Release (DR1; originally scheduled for October 2026) has now been revised.
The plan now is for DR1 to happen in stages, with a first tranche to occur in November 2026 (precise date yet to be announced). The complete data release will take place in mid-2027 (probably in June). The sky area covered by DR1 will be about covering a large sky area of about 1900 deg².
To give a little more background, the data products from the Euclid survey are divided into three levels of data processing function:
LE1 – the “raw” data frames, prior to calibration, generated at the Science Operations Centre from the time-ordered data and telemetry received from the spacecraft
LE2 – the calibrated and corrected data for the two instruments (VIS and NISP) – images, spectra, catalogues of point sources, etc
LE3 – the high-level data products (galaxy catalogues, cosmic shear maps, etc) designed for cosmological analysis
The first release will comprise LE1 and LE2 only. This will be called DR-Foundation. The LE3 data will be added next year to make the full DR1. Since LE3 is required for the cosmological analysis that is the prime motivation for the Euclid mission, it follows that there will be no official cosmology results from Euclid DR1 until mid-2027 at the earliest. Other results based on “Foundation” data may of course emerge before then.
I hope this clarifies the situation.
P.S. Irish physicists and astronomers will be particularly interested to know that the LE1 data includes information about the spacecraft and instrument pointing orientations, which is stored in the form of quaternions…
I’ve been slow onto a result which was announced last week concerning the detection weak gravitational lensing in the cluster Abell 2390 by the Euclid spacecraft and its use to determine the distribution of dark matter in the cluster. You can find a full discussion of the result here and the scientific paper is here.
The analysis was based on Early Release Observations of the cluster, a pretty picture of which are shown here:
Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre (CEA Paris-Saclay), G. Anselmi.
(The little blue patches are artefacts caused by internal reflections in the VIS instrument and can be dealt with in software.)
According to general relativity, the presence of any mass bends the path of light passing near it, producing gravitational lensing. The most famous examples of this are the giant arcs and multiple images associated with strong gravitational lensing, but these are very rare as they require good alignment between observer, lens and source.. Most lines of sight in the universe do not satisfy this condition so are in the weak lensing regime. Even in such cases, however, the presence of the foreground mass can be detected, by way of a systematic alignment in the orientation of background sources around the lensing mass. A circular background image would be distorted into an ellipse by this process. Unfortunately galaxies aren’t circular but are approximately elliptical, so the shape of each source is changed from an ellipse to differently shaped ellipse. The distortion is therefore impossible to detect in a single background source because we don’t know the intrinsic orientation of the galaxy, but the distortion of different sources is correlated in a particular way. Weak gravitational lensing is thus an intrinsically statistical measurement, but it provides a way to measure the masses of astronomical objects without requiring assumptions about their composition or dynamical state. Weak gravitational lensing observations are, however technically difficult to carry out and analyse, as one has to be very careful that no correlations are introduced by systematic errors in the optics.
Anyway, they say that a picture paints a thousand words so here are two pictures. On the left we see the shear axes as extracted from the above image and on the right the inferred dark matter distribution. You can slide the bar backwards and forwards to see how the two images relate.
Shear map (left) and inferred dark matter distribution (right)
You can see that the shear tends to be aligned tangentially to a line connecting the image to the cluster centre (in the plane of the sky), which is what theory would predict.
There’ll be much more of this sort of analysis in the full Euclid Survey. I hope to be able to give an update about this reasonably soon.
A few weeks ago the Euclid Consortium released a printable 3D model of the Euclid Spacecraft. Being a mere theoretician, I don’t know how to operate a 3D printer so I had to ask our technicians if they would make a version for use at open days, etc. The larger version is indeed quite large and everyone has been busy with labs etc, so took a while to print, but thanks to Pat Seery (who did the printing) and Ian McAuley (who assembled and painted the result), here is our model:
The scale for the model is 1:16, so its actual dimensions are 29.5 × 19.5 × 19 cm for the model, and 33 × 20 × 20 cm including the stand. The real thing is over 4.5m tall. There is a little model of an astronaut that comes with the kit (not pictured above) to give an idea of the real size. It’s going to get a protective coat of varnish on it before we use it in public, but it will be a nice addition to our open-day stand and will otherwise be on show in a display case in the Physics Department.
Anyway, if you have access to a 3D printer and would like to make your own version, you can download full instructions here.
A collage of fourteen by eight squares containing examples of gravitational lenses. Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by M. Walmsley, M. Huertas-Company, J.-C. Cuillandre.
I’m sharing the text of a press release from Euclid here to encourage readers to join in this new Zooniverse project.
–o–
In brief
With the launch of Space Warps, a new citizen science project on the Zooniverse platform, you can now join in the search to find rare and elusive strong gravitational lenses in never-before-seen images captured by the European Space Agency’s Euclid space telescope. The project aims at shining a light on dark matter in galaxies and providing clues about mysterious dark energy.
In-depth
Warps in spacetime do not only show up in science fiction movies like Interstellar. In real life, we can see the warping effect that gravity has on spacetime in the form of gravitational lensing.
The enormous gravity of a massive object – such as a galaxy or cluster of galaxies – distorts the shape of spacetime and can bend the light rays coming from a distant galaxy behind. By warping spacetime, the foreground galaxy acts like a magnifying glass.
Light from the background object that would be obscured doesn’t travel in a straight line anymore. Instead, it curves around the intervening mass, often producing multiple images, stretched arcs, or even a complete ring known as ‘Einstein ring’, like the one recently discovered by Euclid.
Strong gravitational lenses offer a striking demonstration of Einstein’s theory of general relativity, showing that matter in the Universe can act as a natural telescope, bringing distant objects into sight.
ESA’s Euclid telescope is revolutionising the studies of strong gravitational lensing by providing very sensitive imaging over large swaths of the sky in unprecedented detail. This is exactly what is needed to identify rare gravitational lenses.
In March 2025, 500 galaxy-galaxy strong lenses were found nestled in just the first 0.04% of Euclid data, most of them previously unknown. This pioneering catalogue was created thanks to the combined effort from citizen scientists, artificial intelligence (AI) and researchers.
Early glimpse of new Euclid images
As Euclid continues its survey, sending around 100 GB of data back to Earth every day, ESA and the Euclid Consortium once again need help from citizen scientists to identify strong gravitational lenses in a large data set.
For this, the Space Warps team has launched a citizen science project based on new Euclid images, which will be part of the future Euclid Data Release 1. While this data is not public yet, by participating in this new citizen science project you can get an early glimpse of these new images of galaxies captured by the telescope.
For this project, you will be inspecting new high quality imaging data from Euclid in which many previously unknown strong lenses are hiding. About three hundred thousand images pre-selected by AI algorithms will be shown, which are fine-tuned with the results from the initial citizen-science Euclid strong lens search. These are the highest ranked candidates from a whopping 72 million galaxies from DR1 that were classified by the AI algorithms. Scientists expect that this exquisite high-quality data will reveal more than 10 000 new lenses.
What can we learn from strong lenses
The Euclid mission explores how the Universe has expanded and how its structure has changed through cosmic history using mainly two methods: weak lensing and baryonic acoustic oscillations. From this, scientists can learn more about the role of gravity and the nature of dark matter and dark energy.
Strong gravitational lenses can also provide insights into these central questions. For example, strong lensing features can ‘weigh’ individual galaxies and clusters of galaxies. This reveals the total matter (whether dark or light) and traces the distribution of dark matter. By studying strong lenses across cosmic time, scientists can trace the expansion of the Universe and its apparent acceleration. This will provide additional insight into the role of dark energy.
“We’ve already seen the success of combining AI with visual inspection by citizen volunteers and scientists on Space Warps, efficiently finding hundreds of high‑probability lens candidates in an initial small Euclid search in 2024”, explains Aprajita Verma, Space Warps’ co-founder and project lead at the University of Oxford, UK. “In this brand new DR1 data, 30 times larger than the initial search and together with our improved AI algorithms, we are expecting to find more than 10 000 high quality lens candidates. This is more than four times the number of lenses than we have been able to find since the first gravitational lens was discovered nearly 50 years ago.”
This step-change is possible thanks to Euclid. The mission can map large areas of the sky with unique sharpness, an ideal combination for finding rare objects like strong gravitational lenses.
“We can’t wait to see what we will find within this unprecedented dataset. Join us on Space Warps to take part in this exciting search!” concludes Aprajita.
Euclid is a European mission, built and operated by ESA, with contributions from NASA. The Euclid Consortium – consisting of more than 2000 scientist from 300 institutes in 15 European countries, the USA, Canada, and Japan – is responsible for providing the scientific instruments and scientific data analysis. ESA selected Thales Alenia Space as prime contractor for the construction of the satellite and its service module, with Airbus Defence and Space chosen to develop the payload module, including the telescope. NASA provided the detectors of the Near-Infrared Spectrometer and Photometer, NISP. Euclid is a medium-class mission in ESA’s Cosmic Vision Programme.
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