Archive for astronomy

Astronomy Envy

Posted in Biographical, Education, Science Politics with tags , , , on July 30, 2026 by telescoper

In 1998 the Department of Physics at the University of Nottingham was struggling in both research and undergraduate recruitment. To remedy the situation it decided to add a new group in Astronomy. The main idea was that having astronomy in its portfolio would attract more students and boost its standing in the Research Assessment Exercise (as it was then called). I was one of the people appointed to turn that decision into reality, and I’m glad to say the result was a success. Undergraduate numbers increased and in the next RAE Nottingham Physics scored a ‘5’, compared to the previous ‘4’. The Astronomy group quickly gained recognition across the UK and abroad, and another group was added, in Astroparticle Physics.

When the new Astronomy group was set up in 1999, the Department of Physics changed its name to the School of Physics & Astronomy. Despite the positive effect of this new activity, it was immediately clear that some members of staff resented it. A new letterhead was created, referring to the School of Physics & Astronomy, and one (very distinguished) senior member of the former Department always crossed off the “and Astronomy” whenever he used it. Others were surprised that the astronomers wanted to do research, when they felt that astronomy was just a bit of window-dressing for undergraduate recruitment. The astronomers were just there to do teaching, so that the “proper physicists” – mostly in semiconductor physics, nanoscience and other areas of condensed matter physics – could spend more time in their laboratories. I’m not saying that every physicist thought this – most were genuinely appreciative and supportive – but there were more than a few grumblers.

The undertone of all this is the envy that some physicists feel towards astronomy. Astronomers get invited to talk about their work to the general public and to amateur astronomy clubs, while there are no such calls for semiconductor physicists. Nobel prizes go to cosmology and astrophysics much more frequently than some would like. Above all there is the view that astronomy is all very well for bringing students in, but once at university the students must be converted to “proper physics”. Astronomers (including astrophysicists and cosmologists) should not get “notions” (as the Irish say). The short-sighted view that scientific research in universities should be aimed at short-term commercial gain amplifies this attitude, but does not entirely account for it.

These thoughts have been at the back of my mind for some time, but they came to the front again with the recent news about cuts to STFC funding. The callous attitude shown to the UK astronomy research community, implying that it should be grateful that it is not being cut by more than the disastrous level announced, indicates (to me) that there’s much more to what is going on than a mere budgetary issue. There is a deliberate plan to slap down a community that has grown too big for its boots.

The consequences for UK astronomy, and UK physics in general, are dire. Astronomy has kept many physics departments afloat for the last several decades. Without it, physics will fail in all but a handful of universities. That’s where envy takes you.

Invisible Rainbows, by Alfredo Carpineti

Posted in Biographical, LGBTQ+, Literature with tags , , , , on July 8, 2026 by telescoper

Today has been a very frustrating day from the point of view of travel – apparently it’s too hot for trains to function – but at least that gave me time to read the book Invisible Rainbows by Dr Alfredo Carpineti (left). This is an engaging and nicely written tour of what we know (and don’t know) about the Universe organized by wavelength of electromagnetic radiation, from radio through microwaves and infrared, to ultraviolet and X-rays to gamma rays. All the wavebands outside the range of human perception, in fact.

What makes this book different from others that have taken the same general approach is that he builds that fairly conventional narrative around conversations with LGBTQIA+ scientists to demonstrate how diverse perspectives have contributed to the advancement of astronomy, astrophysics and cosmology.

There are even a couple of quotes from yours truly, but it’s not just for vanity’s sake that I’m very happy to see this book published. It’s very nicely written and offers a very new perspective on science as a human endeavour. This definitely the first astrophysics book I’ve seen with a dedication “For all the queer kids reaching for the stars”. I guess I was one of those once! The book is at times humorous, even cheeky, but always driven by a passion for astrophysics and the celebration of human diversity. I wish I had I time to read it before Pride Month, but I’m nevertheless very proud to have featured even in a tiny way in such a delightful book.

Finding Easter

Posted in History, The Universe and Stuff with tags , , , , , , on April 3, 2026 by telescoper

As an Astronomist I am often asked “How do they calculate the date of Easter?”, so here goes.

The simple answer is that Easter Sunday is on the first Sunday after the first full Moon on or after the Vernal equinox. The Vernal Equinox took place this year on March 20th and the first full moon after that was on April 2nd.

I say “simple” answer above because it isn’t quite how the date of Easter is reckoned for purposes of the liturgical calendar.

For a start, the ecclesiastical calculation of the date for Easter – the computus – assumes that the Vernal Equinox is always on March 21st, while in reality these days it is more frequently 20th March, like this year.

On top of that there’s the issue of what reference time and date to use. The equinox is a precisely timed astronomical event but it occurs at different times and possibly on different days in different time zones. Likewise the full Moon. In the ecclesiastical calculation the “full moon” does not currently correspond directly to any astronomical event, but is instead the 14th day of a lunar month, as determined from tables (see below). It may differ from the date of the actual full moon by up to two days.

There have been years (1974, for example) where the official date of Easter does not coincide with the date determined by the simple rule given above. The actual rule is a complicated business involving Golden Numbers and Metonic cycles and whatnot.

Here is an excerpt from the Book of Common Prayer that shows Anglicans how to determine the date of Easter for any year up to 2199:

The calculations are based on the approximately 19-year metonic cycle, which is why the above table will not work indefinitely

For this year we find that (2026+1=2027) ÷19=106 with a remainder of 13 (106 × 19 being 2014). The Golden Number for this year is therefore 13, or XIII in the Table. This gives the date of the Paschal Full Moon, which occured this year on 2nd April, which is indeed the day in the centre column next to XIII in the left-hand column in the table. The Sunday Letter is determined by the remainder of (2026+506+6)÷7, which is 4, so this year’s Sunday Letter is D. The date of Easter Sunday is given by the entry in the centre column next to the first occurrence of D in the right-hand column after the Golden Number XIII appears in the left-hand column, i.e. April 5th. I hope this clarifies the situation.

Call for Editors at the Open Journal of Astrophysics

Posted in Open Access with tags , , , , , on February 22, 2026 by telescoper

The number of papers submitted to the Open Journal of Astrophysics continues to rise, as demonstrated by this nice graphic which shows the stats for new submissions for the last five years:

It’s very clear that the thicket is getting thicker! The increasing number of articles is of course very welcome indeed, but it is increasing the load on our Editorial Board and that includes me! I think it’s time therefore to look for more volunteers to join the team, in any area of astrophysics. As a reminder, here are the areas we cover, corresponding to the sections of astro-ph on the arXiv:

  1. astro-ph.GA – Astrophysics of Galaxies. Phenomena pertaining to galaxies or the Milky Way. Star clusters, HII regions and planetary nebulae, the interstellar medium, atomic and molecular clouds, dust. Stellar populations. Galactic structure, formation, dynamics. Galactic nuclei, bulges, disks, halo. Active Galactic Nuclei, supermassive black holes, quasars. Gravitational lens systems. The Milky Way and its contents
  2. astro-ph.CO – Cosmology and Nongalactic Astrophysics. Phenomenology of early universe, cosmic microwave background, cosmological parameters, primordial element abundances, extragalactic distance scale, large-scale structure of the universe. Groups, superclusters, voids, intergalactic medium. Particle astrophysics: dark energy, dark matter, baryogenesis, leptogenesis, inflationary models, reheating, monopoles, WIMPs, cosmic strings, primordial black holes, cosmological gravitational radiation
  3. astro-ph.EP – Earth and Planetary Astrophysics. Interplanetary medium, planetary physics, planetary astrobiology, extrasolar planets, comets, asteroids, meteorites. Structure and formation of the solar system
  4. astro-ph.HE – High Energy Astrophysical Phenomena. Cosmic ray production, acceleration, propagation, detection. Gamma ray astronomy and bursts, X-rays, charged particles, supernovae and other explosive phenomena, stellar remnants and accretion systems, jets, microquasars, neutron stars, pulsars, black holes
  5. astro-ph.IM – Instrumentation and Methods for Astrophysics. Detector and telescope design, experiment proposals. Laboratory Astrophysics. Methods for data analysis, statistical methods. Software, database design
  6. astro-ph.SR – Solar and Stellar Astrophysics. White dwarfs, brown dwarfs, cataclysmic variables. Star formation and protostellar systems, stellar astrobiology, binary and multiple systems of stars, stellar evolution and structure, coronas. Central stars of planetary nebulae. Helioseismology, solar neutrinos, production and detection of gravitational radiation from stellar systems.

We are looking for experienced scientists in any of these areas, and it would be useful to have people who can cover a range of subjects (as some of our existing editors do). As I mentioned here, our most popular area is 1 (Astrophysics of Galaxies) but 2 (Cosmology and NonGalactic Astrophysics) is running it a close second so I’d particular welcome offers from people with expertise in either of those fields, though Editors in any of the areas listed above would be welcome additions.

Since we don’t charge authors or readers we can not offer payment to Editors but it is nevertheless a way of providing a service to the community.

Please get in touch either through the Open Journal website here, or through a message Mastodon here, or BlueSky here. You could even send a message through this form:

← Back

Thank you for your response. ✨

Sunrise, Sunset, Solstice and Perihelion

Posted in The Universe and Stuff with tags , , , , on January 2, 2026 by telescoper

I was on the train earlier today when I remembered that we are getting close to the time when Earth reaches its perihelion, i.e. the point in its orbit when it is closest to the Sun. This occurs at 17.15 GMT tomorrow (Saturday 3rd January 2026), in fact. At this time the distance from the Sun’s centre to Earth’s centre will be 147,099,894 km  This year, aphelion (the furthest distance from the Sun) is at 18.30 GMT on July 6th 2026 at which point the centre of the Earth will be 152,087,774 km from the centre of the Sun. You can find a list of times and dates of perihelion and aphelion for future years here.

Earth’s elliptical orbit viewed at an angle (which makes it look more eccentric than it is – in reality is very nearly circular).

At perihelion the speed of the Earth in its orbit around the Sun is greater than at aphelion (about 30.287 km/s versus 29.291 km/s). This difference, caused by the Earth’s orbital eccentricity, contributes to the difference between mean time and solar time which, among other things, influences the time of sunrise and sunset at the winter solstice that happened a couple of weeks or so ago.

Incidentally, although the Solstice took place on 21st December, it was not until the end of 2025 that we experienced the latest sunrise. The longest day means neither the latest sunrise nor the earliest sunset. The earliest sunset was actually on December 15th in Dublin.

It surprises me how many people think that the existence of the seasons has something to do with the variation of the Earth’s distance from the Sun, thinking that the closer to the Sun we get the warmer the weather will be. The fact that perihelion occurs in the depth of winter should convince anyone living in the Northern hemisphere that this just can’t be the case, as should the fact that it’s summer in the Southern hemisphere while it is winter in the North.

The real reason for the existence of seasons is the tilt of the Earth’s axis of rotation. I used to do a little demonstration with a torch – flashlight to American readers- to illustrate this when I taught first-year astrophysics. If you shine a torch horizontally at a piece of card it will illuminate a patch of the card. Keep the torch at the same distance but tilt the card and you will see the illuminated patch increase in size. The torch is radiating the same amount of energy but in the second case that energy is spread over a larger area than in the first. This means that the energy per unit area incident on the card is decreases when the card is tilted. It is that which is responsible for winter being colder than summer. In the summer the Sun is higher in the sky (on average) than in winter. From this argument you can infer that the winter solstice not the perihelion, is the relevant astronomical indicator of winter.

That is not to say that the shape of the Earth’s orbit has no effect on terrestrial temperatures. It may, for example, contribute to the summer in the Southern hemisphere being hotter than in the North, although it is not the only effect. The Earth’s surface possesses a significant North-South asymmetry: there is a much larger fraction of ocean in the Southern hemisphere, for example, which could be responsible for moderating any differences in temperature due to insolation. The climate is a non-linear system that involves circulating air and ocean currents that respond in complicated ways and on different timescales not just to insolation but to many other parameters, including atmospheric composition (especially the amount of water vapour).

The dates when Earth reaches the extreme points on its orbit (the apsides) are not fixed because of the variations in its orbital eccentricity so, in the short-term, the dates can vary up to 2 days from one year to another. The perihelion distance varies slightly from year to year too; it will be slightly larger next year than this year, for example. There is however a long-term trend for perihelion to occur later in the year. For example, in 1246, the December Solstice (Winter Solstice for the Northern Hemisphere) was on the same day as the Earth’s perihelion. Since then, the perihelion and aphelion dates have drifted by an average of one day every 58 years. This trend will continue, meaning that by the year 6430 the timing of the perihelion and the March Equinox will coincide, although I hope to have retired by then…

MAUVE Image Simulation

Posted in The Universe and Stuff with tags , , , on December 2, 2025 by telescoper

Since the successful launch of the MAUVE satellite on Friday, the telescope has been undergoing verification and calibration. Meanwhile, I’ve been hard at work using my advanced image processing skills to simulate what images of astronomical objects seen in other wavebands might look like using MAUVE.

Here’s an example.

The original picture below is a famous image that needs no introduction. Simply move the slider to the left to reveal the MAUVE version…

P.S. Apologies that the software does not quite scale the images correctly.

Beginning Astronomy

Posted in Biographical with tags , on October 14, 2025 by telescoper

I have a two-hour lecture coming up after which I have immediately to dash to the airport in order to embark on a trip to a foreign country, so in lieu of a proper post here is a nice cartoon I saw on Mastodon.

Natasha Jay 🇪🇺

School Parents Night vs Astronomy Conference

By Tom Gauld in “Physics for Cats”

The first panel shows a parent-teacher conference ("School Parents' Night") where a teacher is giving a girl's parents a failing F grade for their daughter. The second panel shows an "Astronomy Conference" where the same girl, now an adult, is being awarded a medal for her work.
October 12, 2025, 4:31 pm 548 boosts 772 favorites

This also allowed me to check whether the embed facility works, which it seems to do. This actually gives me an idea about how to speed up my weekend updates, which I might try out on Saturday.

The Nebra Sky Disc

Posted in Art, History, The Universe and Stuff with tags , , , , on September 19, 2025 by telescoper
By Frank Vincentz – Public Domain, https://commons.wikimedia.org/w/index.php?curid=117229202

This remarkable object is made of bronze, is around 30 cm diameter and weighs about 2.2 kg. It has a blue-green patina and is inlaid with gold symbols, usually interpreted as the full moon, a lunar crescent, and stars, including a cluster of seven stars, thought to represent the Pleiades. The gold arc on the right probably represents the Sun’s path between the solstices; the angle subtended by the arc (82°) is the correct angle sunrise at the summer and winter solstices and at the latitude of the discovery site (Mittelberg, near Nebra, in Germany); there was probably another such arc on the other side of the disk (now lost). Remarkably, the tin used in making the bronze from which it is formed has been traced by metallurgical analysis to Cornwall.

The Nebra disc has been dated to c. 1800–1600 BCE (Bronze Age) which makes it the oldest (certain) depiction of celestial phenomena known from anywhere in the world. In November 2021, a replica of the Nebra Sky Disc was taken by German astronaut Matthias Maurer to the International Space Station.

Farewell to Gaia

Posted in The Universe and Stuff with tags , , , , on January 15, 2025 by telescoper
Artist impression of ESA’s Gaia satellite observing the Milky Way. The background image of the sky is compiled from data from more than 1.8 billion stars. Spacecraft: ESA/ATG medialab; Milky Way: ESA/Gaia/DPAC. Acknowledgement: A. Moitinho

Today (15th January 2025) marks the end of an era. The European Space Agency’s Gaia spacecraft stops taking data today as it is running out of the gas propellant needed to keep it scanning the sky. The spacecraft was launched on 19 December 2013 so has been operating for just over 11 years.

For those of you not in the know, Gaia is a global space astrometry mission, whose mission was to make the largest, most precise three-dimensional map of our Galaxy by surveying more than a billion stars. Gaia was to monitor each of its target stars about 70 times over a five-year period. Alongside this core mission, it has also discovered hundreds of thousands of new celestial objects, such as extra-solar planets and brown dwarfs, and observed hundreds of thousands of asteroids within our own Solar System.

Gaia is creating an extraordinarily precise three-dimensional map of more than a thousand million stars throughout our Galaxy (The Milky Way) and beyond, mapping their motion, luminosity, temperature and chemical composition as well as any changes in such properties. This huge stellar census will provide the data needed to tackle an enormous range of important problems related to the origin, structure and evolutionary history of our Galaxy. Gaia does this by repeatedly measuring the positions of all objects down to an apparent magnitude of 20. A billion stars is about 1% of the entire stellar population of the Milky Way.

For the brighter objects, i.e. those brighter than magnitude 15, Gaia  measures their positions to an accuracy of 24 microarcseconds, comparable to measuring the diameter of a human hair at a distance of 1000 km. Distances of relatively nearby stars are measured to an accuracy of 0.001%. Even stars near the Galactic Centre, some 30,000 light-years away, have their distances measured to within an accuracy of 20%.

The huge quantity of high-precision data Gaia has produced constitutes a tremendously influential resource for astronomical research. The fourth data release from Gaia, DR4, is in the pipeline for completion soon but the final data release (DR5) will take some years to appear, so this is by no means the last we will hear from Gaia, but the end of observations does close a significant chapter. Its legacy will be immense.

New Results from DESI

Posted in Barcelona, The Universe and Stuff with tags , , , , , , , on November 20, 2024 by telescoper
The Mayall Telescope at Kitt Peak, in which DESI is housed. This PR image was taken during a meteor shower, which is not ideal observing conditions. Picture Credit: KPNO/NOIRLab/NSF/AURA/R. Sparks

I’ve just got time between meetings to mention that a clutch of brand new papers has emerged from the DESI (Dark Energy Spectroscopic Instrument) Collaboration. There is a press release discussing the results from the Lawrence Berkeley Laboratory here and one from the ICCUB in Barcelona here; several members of the group I visited there during sabbatical are working on DESI. Congratulations to them.

I haven’t had time to read them yet, but a quick skim suggests that the results are consistent with the standard cosmological model.

The latest batch contains three Key Publications:

together with the companion supporting papers:

The links lead to the arXiv version of these papers. These articles can also be found, along with previously released publications by the DESI Collaboration, here.

Anyone who has read the latest papers is welcome to comment through the box below!