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.
The Summer Solstice in the Northern hemisphere takes took place this morning, Sunday21st June 2026, at 9.24am local Irish Time (08.24 UTC). Among other things, this means that tomorrow is the longest day of the year around these parts. According to this website, the interval between sunrise and sunset in Dublin today will be 17 hours 4 minutes and 52 seconds. which is 2 seconds longer than yesterday, while tomorrow will be two whole seconds shorter.
The Earth orbits the Sun once a year in a nearly circular orbit. The Earth’s axis of rotation (the straight line through the center of the Earth between the north and south poles) is not perpendicular to the plane of the Earth’s orbit. The Earth’s axis is tilted by about 23.4° from the the direction perpendiular to the orbital plane:
The orientation of the Earth’s axis in space remains nearly constant even as the Earth revolves around the Sun. It always points in the general direction of the star Polaris. The result is that when the Earth is on one side of its orbit, the South Pole is tilted toward the Sun (by as much as 23.4°) and the Southern Hemisphere experiences summer. Six months later, when the Earth is on the opposite side of its orbit, the North pole is tilted toward the Sun (by as much as 23.4°) and the Northern Hemisphere experiences summer.
On the Summer Solstice, Earth’s maximum axial tilt toward the Sun is 23.4°. Likewise, the Sun’s declination from the celestial equator is 23.4°. In areas outside the tropics, the Sun reaches its highest elevation angle at solar noon on the summer solstice. At the North Pole the Sun doesn’t set at all on the Summer Solstice.
So in a sense it’s all downhill from today until the Winter Solstice in December, but the nights won’t start drawing in just yet. Days will indeed get shorter from tomorrow, although this does not mean that sunset will happen earlier tomorrow than it does today. In fact it is a little later; the latest sunset will be on 25th June. Nor does it mean that today sees the earliest sunrise. Sunrise this morning was a little later than yesterday; the earliest sunrise was actually on 17th June.
This arises because there is a difference between mean solar time (measured by clocks) and apparent solar time (defined by the position of the Sun in the sky), so that a solar day does not always last exactly 24 hours. A description of apparent and mean time was given by Nevil Maskelyne in the Nautical Almanac for 1767:
Apparent Time is that deduced immediately from the Sun, whether from the Observation of his passing the Meridian, or from his observed Rising or Setting. This Time is different from that shewn by Clocks and Watches well regulated at Land, which is called equated or mean Time.
The discrepancy between mean time and apparent time arises because of the Earth’s axial tilt and the fact that it travels around the Sun in an elliptical orbit in which its orbital speed varies with time of year (being faster at perihelion than at aphelion).
You can read a piece about the cultural importance of the solstice over the years here.
It’s Saturday again so it’s time for another update of activity at the Open Journal of Astrophysics. Since the last update we have published a further three papers, bringing the number in Volume 9 (2026) to 126 and the total so far published by OJAp up to 574.
I will continue to include the posts made on our Mastodon account (on Fediscience); these announcements also show the DOI for each paper.
The first paper to report this week, published on Monday 15th June, is “SN 2025adpq: A Type Ia supernova in a collisional ring formed during a major galaxy merger” by Brendan O’Connor (Carnegie Mellon University, USA) and 18 others based in the USA, Germany and Australia. The study reports the discovery of a Type Ia supernova, SN 2025adpq, within a collisional ring formed by a major galaxy merger., offset from the nucleus of the primary galaxy. It is published in the folder Astrophysics of Galaxies.
The overlay for this paper is here
You can find the officially accepted version on arXiv here and the announcement on Fediverse here:
New Publication at the Open Journal of Astrophysics: "SN 2025adpq: A Type Ia supernova in a collisional ring formed during a major galaxy merger" by Brendan O'Connor (Carnegie Mellon University, USA) and 18 others based in the USA, Germany and Australia
The second paper for this week, published on Tuesday June 16th in the folder Astrophysics of Galaxies is “The Colors of Ices: Measuring ice column density through photometry” by Adam Ginsburg (U. Florida, USA) and ten others based in the USA, Germany and Spain. This study demonstrates that JWST photometry can identify and quantify interstellar ices, using new open-source models, interstellar ices, finding significant abundance in non-star-forming gas, suggesting many avenues for further research.
The overlay looks like this:
The official version of the paper can be found on arXiv here and the Fediverse announcement here:
New Publication at the Open Journal of Astrophysics: "The Colors of Ices: Measuring ice column density through photometry" by Adam Ginsburg (U. Florida, USA) and ten others based in the USA, Germany and Spain
New Publication at the Open Journal of Astrophysics: "The Non-Gaussian Weak-Lensing Likelihood: A Multivariate Copula Construction and Impact on Cosmological Constraints" by Veronika Oehl and Tilman Tröster (ETH Zurich, Switzerland)
The fourth and final paper of the week, also ublished on Wednesday 17th June but in the folder Astrophysics of Galaxies, is “Black Hole Feedback, Galaxy Quenching and Outflows at Cosmic Dawn: Analysis of the SEEDZ Simulations” by Lewis R. Prole (Maynooth University, Ireland) and 15 others based in Ireland, Germany, USA and UK. The study analyzes the growth and feedback effects of massive black holes in SEEDZ simulations, suggesting that black hole feedback, not nearby supernovae or gas exhaustion, limits initial growth.
The overlay is here:
The final, accepted version can be found on arXiv here and the Mastodon announcement is here:
New Publication at the Open Journal of Astrophysics: "Black Hole Feedback, Galaxy Quenching and Outflows at Cosmic Dawn: Analysis of the SEEDZ Simulations" by Lewis R. Prole (Maynooth University, Ireland) and 15 others based in Ireland, Germany, USA and UK.
And that concludes this week’s update. It has been a slow week on the publishing front, but the main reason is that we have a big backlog of papers accepted but waiting for the authors to put their final versions on arXiv and we can’t do anything about that! I’ll do another update next Saturday.
Many moons ago I wrote a paper with a person called Anthony J.M. Garrett with the title Bayesian Inductive Inference and the Anthropic Cosmological Principle; the full reference is A.J.M. Garrett and P. Coles, Comments on Astrophysics 17(1) 23-47 (1993). It got a few citations here and there, and has been discussed in a few books and other texts. In 1999, the journal Comments on Astrophysics was merged with some other journals to form Comments on Modern Physics which was then acquired by publishers Taylor and Francis in 2001, when it took over Gordon and Breach. The new publisher never put the old papers online in digital format. Most of the back catalogue of Comments on Astrophysics is indexed in NASA/ADS (bibstem: ComAp), but No. 1 of Volume 17 is not there. That classic paper is not, as far as I know, available anywhere on the internet. Or at least it wasn’t until now.
I was recently asked for a PDF of the paper so I made a scan and sent it. Now that I have a scan, however, and WordPress now has a PDF upload gadget, I thought I’d put it up here. I did a Google search for it earlier this evening and the AI Summary described the paper as “seminal”, which just goes to show that AI isn’t always wrong!
Apologies that it’s a bit grubby and wonky, but the scan is made from an old photocopy. I did have a proper offprint somewhere, but I can’t find it.
The real reason for doing this post, however, is to use it as a counter-example to something people often bring up when I criticize academic publishers: “..but they curate the literature!”. They don’t, actually. Libraries do that. The Garrett-Coles paper is available as a hard copy in libraries, but the publisher has nothing to do with that!
P.S. I did a blog post a while ago based on part of the paper.
P.P.S. If I get time I’ll contact ADS to see if they want to put this up in the official biblipgraphic collection…
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…
Many moons ago, just before I moved from Cardiff for my stint at Sussex University, I decided to ditch all the unsolicited letters and manuscripts I’ve accumulated over the years about “alternative” theories of relativity, cosmology, and whatnot. I don’t know why I had kept so many of them for so long, but I no longer have most of them. I did keep one or two of the best ones, however. Here’s an example:
I could never make head nor tail of this, but sometimes had a vague feeling that it might just be a sort of cosmic Rosetta Stone, offering up the Secrets of the Universe in diverse languages. Sadly, however, it’s more likely that the languages involved are Balderdash, Gibberish and Gobbledegook. At the time I wrote:
I regret to announce, therefore, that the plethora of papers telling me why Einstein was wrong, how the Universe is really in the shape of a spiral, how the Great Pyramid of Giza explains the Higgs Boson, and why the Big Bang couldn’t have happened, will have to go to the Great Shredder in the Sky (if that’s where it is).
Anyway, to all my correspondents all I can say is that I’ve enjoyed reading your letters – you must be very fond of your old typewriters – and I’m grateful for the time you took to draw the diagrams by hand in so many lovely colours. And I’m impressed by your qualifications as Electrical Engineers. Really. I’m sorry I didn’t reply to you all individually, but I just didn’t have the time. And now it pains me to realise I don’t have the space either…
I still get such things, of course, but they always come by email nowadays and usually end up in the spam folder, where I do not disturb them. I never reply, of course. Life’s too short.
I know I’m not the only one to have noticed the fact that many – indeed most – such correspondents are Electrical Engineers (usually retired). I was delighted therefore to see that there’s now a nice little paper on arXiv by David Garfinkle with the title Relativity for Retired Engineers and the abstract:
We provide some guidance and examples to clear up common misconceptions about special relativity. These misconceptions often come from trying to express the truths of special relativity in Newtonian terms rather than in terms more natural to special relativity itself. This conceptual stance can also help in attaining a better understanding of general relativity.
Readers may consider referring their correspondents to this source…
It’s Saturday again so it’s time for another update of activity at the Open Journal of Astrophysics. Since the last update we have published a further three papers, bringing the number in Volume 9 (2026) to 122 and the total so far published by OJAp up to 570.
I will continue to include the posts made on our Mastodon account (on Fediscience); these announcements also show the DOI for each paper.
The first paper to report this week, published on Thursday 11th June, is “Dancing Streams In Merging Halos: Stellar Streams in a MW–LMC-like merger” by (all based in the USA): Sachi Weerasooriya (Carnegie Observatories), Tjitske Starkenburg (Northwestern U.), Emily C. Cunningham (Columbia U.) & Kathryn V. Johnston (Flatiron Institute). This article explores how galaxy mergers, like the Milky Way-Large Magellanic Cloud merger, significantly alter the properties and structures of stellar streams, challenging the recovery of their initial orbits. It is in the folder marked Astrophysics of Galaxies.
The overlay for this paper is here
You can find the officially accepted version on arXiv here and the announcement on Fediverse here:
New Publication at the Open Journal of Astrophysics: "Dancing Streams In Merging Halos: Stellar Streams in a MW–LMC-like merger" by (all based in the USA): Sachi Weerasooriya (Carnegie Observatories), Tjitske Starkenburg (Northwestern U.), Emily C. Cunningham (Columbia U.) & Kathryn V. Johnston (Flatiron Institute).
New Publication at the Open Journal of Astrophysics: "X-SORTER (X-ray Survey Of meRging clusTErs in Redmapper): X-ray and Spectroscopic Characterization of 12 Optically Selected Galaxy Cluster Merger Candidates" by Christopher Hopp, David Wittman, Rodrigo Stancioli, Zhuoran Gao & Faik Bouhrik (UC Davis) and Scott Adler (Rochester), all based in the USA.
The third and final paper of the week, published on Friday 12th June in the folder Earth and Planetary Astrophysics, is “JCMT Constraints on the Early-Time HCN and CO Emission and HCN Temporal Evolution of 3I/ATLAS” by Jason T. Hinkle (U. Illinois, USA) and 6 others based in the USA and Chile. This article presents observations of the third Interstellar Object, 3I/ATLAS, providing early sub-mm constraints on its activity. The findings suggest a steeper production rate slope than typical Solar System comets.
The overlay for this one is here:
The final, accepted version can be found on arXiv here and the Mastodon announcement is here:
New Publication at the Open Journal of Astrophysics: "JCMT Constraints on the Early-Time HCN and CO Emission and HCN Temporal Evolution of 3I/ATLAS" by Jason T. Hinkle (U. Illinois, USA) and 6 others based in the USA and Chile.
And that concludes this week’s update. It has been a slow week on the publishing front, but the main reason is that we have a big backlog of papers accepted but waiting for the authors to put their final versions on arXiv and we can’t do anything about that! I’ll do another update next Saturday.
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.
Another Saturday, another update of activity at the Open Journal of Astrophysics. Since the last update we have published a further five papers, bringing the number in Volume 9 (2026) to 119 and the total so far published by OJAp up to 567.
I will continue to include the posts made on our Mastodon account (on Fediscience); these announcements also show the DOI for each paper.
The first paper to report this week, published on Tuesday 2nd June, is “The impact of the formation channel on gravitational-wave-galaxy cross-correlations” by Kabir Chakravarti (Chennai Mathematical Institute, India) and Federico R Urban (CEICO-FZU, Czech Republic). This article, published in the folder Cosmology and Nongalactic Astrophysics, explores how uncertainties in binary formation affect the cross-correlation signal between gravitational wave events and galaxy catalogues, finding that time-delay distribution significantly impacts the signal.
The overlay for this paper is here
You can find the officially accepted version on arXiv here and the announcement on Fediverse here:
New Publication at the Open Journal of Astrophysics: "The impact of the formation channel on gravitational-wave-galaxy cross-correlations" by Kabir Chakravarti (Chennai Mathematical Institute, India) and Federico R Urban (CEICO-FZU, Czech Republic)
New Publication at the Open Journal of Astrophysics: "Transient X-ray Sources as Extremely Eccentric Mass-Transfer Binaries with Compact Companions" by Jonathan I Katz and Michael A Nowak (Washington University, USA)
Next one up, the third paper of the week, also published on Tuesday 2nd June in the folder High-Energy Astrophysical Phenomena is “Resolving the (Debate About) Nozzle Shocks in Tidal Disruption Events” by Zachary L. Andalman & Eliot Quataert (Princeton U., USA), Eric R. Coughlin (Syracuse U. USA) and C. J. Nixon (U. Leeds, UK). This paper presents a model to understand the role of nozzle shocks in the circularization of stellar debris during a tidal disruption event when a star approaches a supermassive black hole (SMBH)
The overlay for this one is here:
The final, accepted version can be found on arXiv here and the Mastodon announcement is here:
New Publication at the Open Journal of Astrophysics: "Resolving the (Debate About) Nozzle Shocks in Tidal Disruption Events" by Zachary L. Andalman & Eliot Quataert (Princeton U., USA), Eric R. Coughlin (Syracuse U. USA) and C. J. Nixon (U. Leeds, UK)
The fourth paper this week, published on Wednesday 3rd June in the folder Cosmology and Nongalactic Astrophysics, is “Validating Digital Twins of the Local Universe with the Thermal Sunyaev-Zel’dovich Signal” by Richard Stiskalek (University of Oxford, UK) and Harry Desmond (University of Portsmouth, UK). The thermal Sunyaev-Zel’dovich effect and constrained simulations are used to analyze the thermal pressure of ionized gas in galaxy clusters and produce a set of digital twins for cosmological study.
The overlay is here:
The officially accepted version can be found on arXiv here and here is the Mastodon announcement:
New Publication at the Open Journal of Astrophysics: "Validating Digital Twins of the Local Universe with the Thermal Sunyaev-Zel’dovich Signal" by Richard Stiskalek (U. Oxford, UK) and Harry Desmond (U. Portsmouth, UK)
New Publication at the Open Journal of Astrophysics: "Photon (Non)Conservation in the Reduced Speed of Light Approximation and How to (Almost) Fix It" by Nickolay Y. Gnedin (U. Chicago, USA)
Here’s an invitation to people interested in astronomy to join staff from the Department of Physics at Maynooth University on Wednesday, August 12th 2026 from 5:30 pm to 8:30 pm for a special public celebration of one of the deepest solar eclipses visible from Ireland in decades. The next eclipse with > 90% obscuration of the Sun by the Moon won’t be seen again in Ireland until 2090, by which time I will have retired.
Experience the eclipse safely through:
eclipse viewing glasses
solar telescopes
live astronomy demonstrations
List of Solar Talks during the evening:
Dr. Emma Whelan – The Story of the Sun
Dr. Joshuah Heath – The Quantum Sun
Dr. Marcin Gradziel – (Electric) Power from the Sun. The good, the bad, and the glinty!
Dr. Michelle McCrystall – The star of the show: How the Sun drives our climate
Prof. Peter Coles – Einstein and the Eclipse (Who He? Ed.)
Dr. Patrick Kavanagh – Will our Sun go Supernova?
The evening will also include:
an immersive* astronomy show in our inflatable planetarium
hands-on arts and crafts activities for children
*especially if it rains
Maynooth University Staff can reserve a place here until June 14th, after which booking will be opened to the general public – I’ll repost this invitation with a link at that time.
The views presented here are personal and not necessarily those of my employer (or anyone else for that matter).
Feel free to comment on any of the posts on this blog but comments may be moderated; anonymous comments and any considered by me to be vexatious and/or abusive and/or defamatory will not be accepted. I do not necessarily endorse, support, sanction, encourage, verify or agree with the opinions or statements of any information or other content in the comments on this site and do not in any way guarantee their accuracy or reliability.
In the Dark 
Bayesian Inductive Inference and the Anthropic Cosmological Principle
Posted in The Universe and Stuff with tags Anthropic Cosmological Principle, Antony J.M. Garrett, Bayesian Inductive Inference, Comments on Astrophysics 17(1) 23-47, Gordon and Breach, NASA/ADS, Taylor and Francis on June 17, 2026 by telescoperMany moons ago I wrote a paper with a person called Anthony J.M. Garrett with the title Bayesian Inductive Inference and the Anthropic Cosmological Principle; the full reference is A.J.M. Garrett and P. Coles, Comments on Astrophysics 17(1) 23-47 (1993). It got a few citations here and there, and has been discussed in a few books and other texts. In 1999, the journal Comments on Astrophysics was merged with some other journals to form Comments on Modern Physics which was then acquired by publishers Taylor and Francis in 2001, when it took over Gordon and Breach. The new publisher never put the old papers online in digital format. Most of the back catalogue of Comments on Astrophysics is indexed in NASA/ADS (bibstem: ComAp), but No. 1 of Volume 17 is not there. That classic paper is not, as far as I know, available anywhere on the internet. Or at least it wasn’t until now.
I was recently asked for a PDF of the paper so I made a scan and sent it. Now that I have a scan, however, and WordPress now has a PDF upload gadget, I thought I’d put it up here. I did a Google search for it earlier this evening and the AI Summary described the paper as “seminal”, which just goes to show that AI isn’t always wrong!
Anyway, here is a scanned PDF of the paper:
Apologies that it’s a bit grubby and wonky, but the scan is made from an old photocopy. I did have a proper offprint somewhere, but I can’t find it.
The real reason for doing this post, however, is to use it as a counter-example to something people often bring up when I criticize academic publishers: “..but they curate the literature!”. They don’t, actually. Libraries do that. The Garrett-Coles paper is available as a hard copy in libraries, but the publisher has nothing to do with that!
P.S. I did a blog post a while ago based on part of the paper.
P.P.S. If I get time I’ll contact ADS to see if they want to put this up in the official biblipgraphic collection…
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