Archive for the The Universe and Stuff Category

« Older Entries
Newer Entries »

Weekly Update from the Open Journal of Astrophysics – 18/01/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , on January 18, 2025 by telescoper

It’s Saturday morning so once again it’s time for an updated of papers published at the Open Journal of Astrophysics. Since the last update we have published three new papers which brings the number in Volume 8 (2025) up to 7 and the total so far published by OJAp up to 242.

In chronological order of publication, the three papers published this week, with their overlays, are as follows. You can click on the images of the overlays to make them larger should you wish to do so.

First one up is “Potential-density pairs for Galaxy discs with exponential or sech^2 vertical profile” by Walter Dehnen and Shera Jafaritabar (Heidelberg, Germany). This paper was published on Tuesday 14th January 2025 in the folder marked Astrophysics of Galaxies. It presents a new set of analytic models for the structure of disc galaxies. The overlay, which includes the abstract, is here:

You can find the officially accepted version of this paper on arXiv here.

The second paper, which was published on Thursday 17th January 2025 also in the folder Astrophysics of Galaxies, is “Quantifying Bursty Star Formation in Dwarf Galaxies” by Yuan-Sen Ting (Ohio State University) and Alexander Ji (U. Chicago). This paper describes an application of Gaussian mixture models to distinguish between discontinuous and continuous star formation histories in dwarf galaxies.

Here is a screen grab of the overlay, which includes the abstract:You can find the officially accepted version of the paper on the arXiv here.

The third paper to announce, also published on 17th January 2025 but in the folder Cosmology and NonGalactic Astrophysics, is “Fast Projected Bispectra: the filter-square approach” by Lea Harscouet, Jessica A. Cowel, Julia Ereza & David Alonso (Oxford U., UK), Hugo Camacho (Brookhaven National Laboratory, USA), Andrina Nicola (Bonn, Germany) and Anže Slosar (Brookhaven). This paper presents Presenting the filtered-squared bispectrum (FSB), a fast and robust estimator of the projected bispectrum for use on cosmological data sets.

You can see the overlay here:

The accepted version of this paper can be found on the arXiv here.

That’s all for this week. I’ll do another update next Saturday.

1 Comment »

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.

2 Comments »

Weekly Update from the Open Journal of Astrophysics – 11/01/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , on January 11, 2025 by telescoper

Welcome to the first update of 2025 from the Open Journal of Astrophysics. For the new year we have started Volume 8. Since the last update of 2024 we have published four new papers which brings the total so far published by OJAp up to 239.

In chronological order of publication, the four papers published this week, with their overlays, are as follows. You can click on the images of the overlays to make them larger should you wish to do so.

First one up is “Weak-Lensing Shear-Selected Galaxy Clusters from the Hyper Suprime-Cam Subaru Strategic Program: I. Cluster Catalog, Selection Function and Mass–Observable Relation” by Kai-Feng Chen (MIT, USA), I-Non Chiu (National Cheng University, Taiwan), Masamune Oguri (Chiba University, Japan), Yen-Ting Lin (IAAAS, Taiwan), Hironao Miyatake (Nagoya, Japan), Satoshi Miyazaki (Nat. Astr. Obs. Japan), Surhud More (IUCAA, India), Takashi Hamana (Nat. Astr. Obs. Japan), Markus M. Rau Carnegie Mellon University, USA), Tomomi Sunayama (Steward Obs., USA), Sunao Sugiyama (U. Penn, USA), Masahiro Takada (U. Tokyo, Japan).

This paper, which was published on Monday 6th January 2025 is in the folder Cosmology and NonGalactic Astrophysics, discusses steps towards towards the extraction of cosmogical constraints from a sample of galaxy clusters selected via weak gravitational lensing

Here is a screen grab of the overlay, which includes the abstract:

You can find the officially accepted version of the paper on the arXiv here.

The second paper to announce, published on 7th January 2025 and also in the folder Cosmology and NonGalactic Astrophysics, is “Cosmology on point: modelling spectroscopic tracer one-point statistics” by Beth McCarthy Gould (Newcastle U., UK), Lina Castiblanco (Bielefeld, Germany), Cora Uhlemann (Bielefeld, Germany), and Oliver Friedrich (LMU, Germany).

You can see the overlay here:

The accepted version of this paper can be found on the arXiv here.

The third paper, published on 9th January 2025, also in the folder Cosmology and NonGalactic Astrophysics, is “Probing Environmental Dependence of High-Redshift Galaxy Properties with the Marked Correlation Function” by Emy Mons and Charles Jose (Cochin University of Science and Technology, India). This paper uses the marked two-point correlation function to measure the environmental dependence of galaxy clustering at high redshift.

Here is the overlay:

The final version accepted on arXiv is here.

Last of this quartet, also published on 9th January 2025, but in the folder Astrophysics of Galaxies is “The infrared luminosity of retired and post-starburst galaxies: A cautionary tale for star formation rate measurements” by Vivienne Wild (St Andrews, UK), Natalia Vale Asari (Universidade Federal de Santa Catarina, Brazil), Kate Rowlands (STScI, Sara L. Ellison (U. Victoria, Canada), Ho-Hin Leung (St Andrews), Christy Tremonti (U. Wisconsin-Madison, USA).

The paper proposes an extension of the semi-analytic formalism to weak lensing and thermal Sunyaev-Zeldovich (tSZ) fields directly on the full-sky, with an emphasis on higher-order correlations. The overlay is here:

You can find the official accepted version on the arXiv here.

That’s all for this week. I’ll do another update next Saturday.

1 Comment »

Failing to Teach Particle Physics

Posted in Biographical, Education, The Universe and Stuff with tags , , , on January 7, 2025 by telescoper

As the Christmas holiday draws to a close and I begin thinking about the possibility that sooner or later, in due course, at some point in the future, in the fullness of time, all things considered, when all is said and done, in the end, I will have to start teaching again. Thinking about this is preferable to thinking about the stack of exam marking that I will have to contend with shortly.

One of the modules I am down to teach in the Spring Semester is particle physics, a subject I haven’t taught for well over a decade, so I have been looking through a box of old notes on the subject. Doing so I remembered that I had to explain neutrino oscillations, a process in which neutrinos (which have three distinct flavour states, associated with the electron, mu and tau leptons) can change flavour as they propagate. It’s quite a weird thing to spring on students who previously thought that lepton number was always conserved so I decided to start with an analogy based on more familiar physics.

A charged fermion such as an electron (or in fact anything that has a magnetic moment, which would include, e.g. the neutron)  has spin and, according to standard quantum mechanics, the component of this in any direction can  can be described in terms of two basis states, say “up” for the +z-direction and “down” for the opposite (-z) represented schematically like this:

In this example, as long as the particle is travelling through empty space, the probability of finding it with spin “up” is  50%, as is the probability of finding it in the spin “down” state, the probabilities defined by the square of the amplitudes. Once a measurement is made, however, the state collapses into a definite “up” or “down” wherein it remains until something else is done to it. In such a situation one of the coefficients goes to zero and the other is unity.

If, on the other hand, the particle  is travelling through a region where there is a magnetic field the “spin-up” and “spin-down” states can acquire different energies owing to the interaction between the magnetic moment of the particle and the magnetic field. This is important because it means the bits of the wave function describing the up and down states evolve at different rates, and this  has measurable consequences: measurements made at different positions yield different probabilities of finding the spin pointing in different directions. In effect, the spin vector of the  particle performs  a sort of oscillation, similar to the classical phenomenon called  precession.

The mathematical description of neutrino oscillations is very similar to this, except it’s not the spin part of the wavefunction being affected by an external field that breaks the symmetry between “up” and “down”. Instead the flavour part of the wavefunction is “precessing” because the flavour states don’t coincide with the eigenstates of the Hamiltonian that describes the neutrinoes. For this to happen, however, different neutrino types must have intrinsically different energies  (which, in turn, means that the neutrinos must have different masses), in quite  a similar way similar to the spin-precession example.

Although this isn’t a perfect analogy I thought it was a good way of getting across the basic idea. Unfortunately, however, when I subsequently asked an examination question about neutrino oscillations I got a significant number of answers that said “neutrino oscillations happen when a neutrino travels through a magnetic field….”.

Sigh.

Neutrinos have no magnetic moment so don’t interact with  magnetic fields, you see…

Anyhow, I’m sure there’s more than one reader out there who has had a similar experience with an analogy that wasn’t perhaps as instructive as hoped. Feel free to share through the comments box…

5 Comments »

Time for Perihelion

Posted in The Universe and Stuff with tags , , , on January 4, 2025 by telescoper

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

At 13.28 GMT today (Saturday 4th January 2025), the Earth reaches its perihelion. At this time the distance from the Sun’s centre to Earth’s centre will be 147,103,686 km. This year, aphelion (the furthest distance from the Sun) is at 20.54 GMT on July 3rd 2025 at which point the centre of the Earth will be 152,087,738 km from the centre of the Sun. You can find a list of times and dates of perihelion and aphelion for future years here.

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.

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 as it moves in its orbit in 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 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 (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’s slightly larger this year than last 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…

1 Comment »

Timescape versus Dark Energy?

Posted in Astrohype, Open Access, The Universe and Stuff with tags , , , , , , , on January 2, 2025 by telescoper

Just before the Christmas break I noticed a considerable amount of press coverage claiming that Dark Energy doesn’t exist. Much of the media discussion is closely based on a press release produced by the Royal Astronomical Society. Despite the excessive hype, and consequent initial scepticism, I think the paper has some merit and raises some interesting issues.

The main focus of the discussion is a paper (available on arXiv here) by Seifert et al. with the title Supernovae evidence for foundational change to cosmological models. This paper is accompanied by a longer article called Cosmological foundations revisited with Pantheon+ (also available on arXiv) by a permutation of the same authors, which goes into more detail about the analysis of supernova observations. If you want some background, the “standard” Pantheon+ supernova analysis is described in this paper. The reanalysis presented in the recent papers is motivated an idea called the Timescape model, which is not new. It was discussed by David Wiltshire (one of the authors of the recent papers) in 2007 here and in a number of subsequent papers; there’s also a long review article by Wiltshire here (dated 2013).

So what’s all the fuss about?

Simulation of the Cosmic Web

In the standard cosmological model we assume that, when sufficiently coarse-grained, the Universe obeys the Cosmological Principle, i.e. that it is homogeneous and isotropic. This implies that the space-time is described by a Friedmann–Lemaître–Robertson–Walker metric (FLRW) metric. Of course we know that the Universe is not exactly smooth. There is a complex cosmic web of galaxies, filaments, clusters, and giant voids which comprise the large-scale structure of the Universe. In the standard cosmological model these fluctuations are treated as small perturbations on a smooth background which evolve linearly on large scales and don’t have a significant effect on the global evolution of the Universe.

This standard model is very successful in accounting for many things but only at the expense of introducing dark energy whose origin is uncertain but which accounts for about 70% of the energy density of the Universe. Among other things, this accounts for the apparent acceleration of the Universe inferred from supernovae measurements.

The standard cosmology’s energy budget

The approach taken in the Timescape model is to dispense with the FLRW metric, and the idea of separating the global evolution from the inhomogeneities. The idea instead is that the cosmic structure is essentially non-linear so there is no “background metric”. In this model, cosmological observations can not be analysed within the standard framework which relies on the FLRW assumption. Hence the need to reanalyse the supernova data. The name Timescape refers to the presence of significant gravitational time-dilation effects in this model as distinct from the standard model.

I wrote before in the context of a different paper:

….the supernovae measurements do not directly measure cosmic acceleration. If one tries to account for them with a model based on Einstein’s general relativity and the assumption that the Universe is on large-scales is homogeneous and isotropic and with certain kinds of matter and energy then the observations do imply a universe that accelerates. Any or all of those assumptions may be violated (though some possibilities are quite heavily constrained). In short we could, at least in principle, simply be interpreting these measurements within the wrong framework…

So what to make of the latest papers? I have to admit that I didn’t follow all the steps of the supernova reanalysis. I hope an expert can comment on this! I will therefore restrict myself to some general comments.

  • My attitude to the standard cosmological model is that it is simply a working hypothesis and we should not elevate it to a status any higher than that. It is based not only on the Cosmological Principle (which could be false), but on the universal applicability of general relativity (which might not be true), and on a number of other assumptions that might not be true either.
  • It is important to recognize that one of the reasons that the standard cosmology is the front-runner is that it provides a framework that enables relatively straightforward prediction and interpretation of cosmological measurements. That goes not only for supernova measurements but also for the cosmic microwave background, galaxy clustering, gravitational lensing, and so on. This is much harder to do accurately in the Timescape model simply because the equations involved are much more complex; there are few exact solutions of Einstein’s equations that can help. It is important that people work on alternatives such as this.
  • Second, the idea that inhomogeneities might be much more important than assumed in the standard model has been discussed extensively in the literature over the last twenty years or so under the heading “backreaction”. My interpretation of the current state of play is that there are many unresolved questions, largely because of technical difficulties. See, for example, work by Thomas Buchert (here and, with many other collaborators here) and papers by Green & Wald (here and here). Nick Kasiser also wrote about it here.
  • The new papers under discussion focus entirely on supernovae measurements. It must be recognized that these provide just one of the pillars supporting the standard cosmology. Over the years, many alternative models have been suggested that claim to “fix” some alleged problem with cosmology only to find that it makes other issues worse. That’s not a reason to ignore departures from the standard framework, but it is an indication that we have a huge amount of data and we’re not allowed to cherry-pick what we want. We have to fit it all. The strongest evidence in favour of the FLRW framework actually comes from the cosmic microwave background (CMB) with the supernovae provide corroboration. I would need to see a detailed prediction of the anisotropy of the CMB before being convinced.
  • The Timescape model is largely based on the non-linear expansion of cosmic voids. These are undoubtedly important, and there has been considerable observational and theoretical activity in understanding them and their evolution in the standard model. It is not at all obvious to me that the voids invoked to explain the apparent acceleration of the Universe are consistent with what we actually see in our surveys. That is something else to test.
  • Finally, the standard cosmology includes a prescription for the initial conditions from which the present inhomogeneities grew. Where does the cosmic web come from in the Timescape model?

Anyway, I’m sure there’ll be a lot of discussion of this in the next few weeks as cosmologists return to the Universe from their Christmas holidays!

Comments are welcome through the box below, especially from people who have managed to understand the cos.

9 Comments »

New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , on December 28, 2024 by telescoper

I wasn’t planning to do the usual weekly update of activity at the Open Journal of Astrophysics this morning as I thought we wouldn’t publish any more papers between last week’s update and the Christmas break. However, one final version did hit the arXiv on Christmas Eve so I decided to publish it straight away. This brings the total for Volume 7 (2024) to 120 – a neat average of ten a month – and the overall total to 235.

Here’s a table showing the sequence of papers published over the last six years and the series formed from the aforementioned sequence:

Year201920202021202220232024
Papers1215171750120
Total16314865115235

Anyway, the new paper is “Galaxy evolution in the post-merger regime. II – Post-merger quenching peaks within 500 Myr of coalescence” by Sara Ellison (U. Victoria, Canada), Leonardo Ferreira (U. Victoria), Vivienne Wild, (St Andrews, UK), Scott Wilkinson (U. Victoria), Kate Rowlands, (STScI, USA) & David R. Patton (Trent U., Canada). It was published on 24th December 2024 in the folder marked Astrophysics of Galaxies. It comprises an investigation of the possibility that quenching of star formation is a consequence of galaxy-galaxy interactions and mergers. The overlay is here:

You can find the officially accepted version on arXiv here.

Well, that definitely concludes the updates for 2024. I’ll be back on January 4th with the first update of 2025.

2 Comments »

Five New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , , on December 21, 2024 by telescoper

Time for the usual Saturday summary of papers at the Open Journal of Astrophysics. We have published five more papers since the last update a week ago. The count in Volume 7 (2024) is now up to 119 and the total altogether to 234. As I mentioned in a post last week this means we have published more papers this year (2024) than in all previous years put together.

In chronological order, the five papers published this week, with their overlays, are as follows. You can click on the images of the overlays to make them larger should you wish to do so.

First one up, published on Wednesday 18th December 2024 is “The picasso gas model: Painting intracluster gas on gravity-only simulations” byby Florian Kéruzoré, L. E. Bleem, N. Frontiere, N. Krishnan, M. Buehlmann, J. D. Emberson, S. Habib, and P. Larsen all of the Argonne National Laboratory, USA.  The paper, which is in the folder marked Cosmology and NonGalactic Astrophysics describes a method using machine learning based on an analytical gas model to predict properties of the intracluster medium.

Here is a screen grab of the overlay, which includes the abstract:

 

 

You can find the officially accepted version of the paper on the arXiv here.

The second paper to announce, and the first of four published on Wednesday 19th December 2024, “maria: A novel simulator for forecasting (sub-)mm observations” by J. van Marrewijk (ESO, Garching, Germany) and 10 others based in Germany, USA, Norway, France and Italy. This paper describes a multi-purpose telescope simulator that optimizes scanning strategies and instrument designs, produces synthetic time-ordered data, time streams, and maps from hydrodynamical simulations, thereby enabling comparison between theory and observations. This one is in the folder marked Instrumentation and Methods for Astrophysics.

You can see the overlay here:

The accepted version of this paper can be found on the arXiv here.

The third paper  is “Detached Circumstellar Matter as an Explanation for Slowly-Rising Interacting Type Ibc Supernovae” by Yuki Takei (Kyoto U., Japan) & Daichi Tsuna (Caltech, USA). This one was also published on 19th December and is in the folder marked High-Energy Astrophysical Phenomena. The overlay is here:

 

 

The officially accepted version can be found on arXiv here.

The fourth paper, also published on 19th December 2024, is called “On the dark matter content of ultra-diffuse galaxies” and was written by Andrey Kravtsov (U. Chicago, USA).  The article discusses the implications of measured velocity dispersions of ultra-diffuse galaxies for models of galaxy formation and is in the folder marked Astrophysics of Galaxies.

The overlay is here

 

You can find the officially accepted version of this paper here.

The fifth paper in this batch is “Estimating Exoplanet Mass using Machine Learning on Incomplete Datasets” by Florian Lalande (Okinawa Institute of Science and Technology), Elizabeth Tasker (Institute of Space and Astronautical Science, Kanagawa) and Kenji Doya (Okinawa); all based in Japan. This one was published on 10th October 2024 in the folder marked Earth and Planetary Astrophysics. It compares different methods for inferring exoplanet masses in catalogues with missing data

 

You can find the official accepted version on the arXiv here.

Finally for this week we have “A new non-parametric method to infer galaxy cluster masses from weak lensing” by Tobias Mistele (Case Western Reserve University, USA) and Amel Durakovic (Czech Academy of Sciences, Czechia). This one was also published on 19th December and is in the folder Cosmology and NonGalactic Astrophysics.  The overlay is here

 

You can find the officially-accepted version on arXiv here.

That’s in for this week. I will do another update next Saturday only if we have any new papers on Monday. I will be taking a break over Christmas and also preparing Volume 8 (2025) for the new year, so publishing will be suspended from 24th December until 2nd January (inclusive). If you want your paper to be published in 2024 the final version must be on arXiv by Monday 23rd December at the latest, otherwise it will be held over until 2025.

 

1 Comment »

The Winter Solstice 2024

Posted in Maynooth, The Universe and Stuff with tags , , , on December 20, 2024 by telescoper
Sunlight at dawn on the Winter Solstice at Newgrange

Just a quick note to point out that the Winter Solstice in the Northern hemisphere happens tomorrow, Saturday 21st December 2024, at 9.21 UT (GMT). I am posting this in advance as I am planning to have a line-in tomorrow morning.

In Dublin, sunrise today (20th December) was at 8.37 am and sunset at 4.07 pm, while tomorrow the sunrise is at 8.38 am and sunset at 4.08 pm. Notice that both sunrise and sunset happen later tomorrow than today, so the Solstice marks neither the latest sunrise nor the earliest sunset: the interval between the two events will, however, be about 2 seconds shorter tomorrow than today. For a full explanation of this, see this older Winter Solstice post.

Anyway, today is has been the last day of teaching at Maynooth University. I did my final lecture of 2024 this morning and attended project presentations this afternoon. Campus has been very quiet all day, most people having already departed for the break. That makes me feel less guilty about going home earlier than usual at 4.15pm. Now it’s time power down everything in my office for the break and head home via the shops!

Leave a comment »

Sonification of a Galaxy

Posted in Euclid, The Universe and Stuff with tags , , , on December 19, 2024 by telescoper

Here’s an intriguing experiment in sonification of an image from Euclid.

And here’s the official blurb about it:

An ethereal dance of misty clouds of interstellar dust with a myriad of distant stars and galaxies speckled like paint drops over a black canvas. This is a sonification of a breathtaking image taken by ESA’s Euclid space telescope of the young star-forming region Messier 78.

The sonification offers a different representation of the data collected by Euclid, and lets us explore the stellar nurseries in M78 through sound. Close your eyes and listen to let the cosmic image be drawn by your mind’s eye, or watch as the traceback line in this video follows the sounds to colour the image from left to right.

The twinkling sounds of various pitches and volumes represent the galaxies and stars in the frame. The pitch of the sound points towards where we see the dot of light in the image. Higher pitches tell us that a star or galaxy appears further at the top in the image along the traceback line.

The brightness of these objects in and around M78 are represented by the volume of the twinkles. Whenever we hear a particularly loud clink, the star or galaxy that Euclid observed appears particularly bright in the image.

Underlying these jingling sounds, we can hear a steady undertone, made up of two chords which represent different regions in Messier 78. This sound intensifies as the traceback line approaches first the brightest, and later the densest regions in the nebula.

The first two deeper crescendos in this undertone indicate two patches in the image where the most intense colour is blue/purple. These appear as two ‘cavities’ in M78, where newly forming stars carve out and illuminate the dust and gas in which they were born.

The chords intensify a third time at a slightly higher pitch corresponding to the red-orange colours in the image, as the sound draws over the densest star-forming region of the frame. This stellar nursery is hidden by a layer of dust and gas that is so thick that it obscures almost all the light of the young stars within it.

As the sound traces over the entire Euclid image, these different tones together form a cosmic symphony that represents the image of Messier 78, and the stars and galaxies that lie behind and within it. You can read more about this image that was first revealed to the eyes of the world earlier this year here: https://www.esa.int/Science_Explorati…

Many thanks to Klaus Nielsen (DTU Space / Maple Pools) for making the sonification in this video. If you would like to hear more sonifications and music by this artist, please visit: https://linktr.ee/maplepools

P.S. The first sentence of the Wikipedia page on sonification uses the word “perceptualize”. Ugh!

1 Comment »

« Older Entries
Newer Entries »