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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…

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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.

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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.

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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.

 

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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!

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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!

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Four New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , , on December 14, 2024 by telescoper

It’s Saturday morning once again so here’s another quick update of activity at the Open Journal of Astrophysics. Since the last update a week ago we have published  four papers, which takes the count in Volume 7 (2024) up to 114 and the total published altogether by OJAp up to 229. If we publish just one more paper between now and the end of the year, we will have published as many papers in 2024 as we have in all previous years.

Anyway, 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 “Star formation beyond galaxies: widespread in-situ formation of intra-cluster stars” by Niusha Ahvazi & Laura V. Sales (UC Riverside, USA), Julio F. Navarro (U. Victoria, Canada), Andrew Benson (Carnegie Obs. USA), Alessandro Boselli (Aix Marseille U., France) and Richard D’Souza (Vatican Obs.). The paper, which is in the folder marked Astrophysics of Galaxies, The paper presents a simulation-based analysis of a diffuse star forming component in galaxy clusters extending for hundreds of kiloparsecs and tracing the distribution of neutral gas in the cluster host halo.

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 10th December 2024 in the folder Cosmology and NonGalactic Astrophysics, is “Cosmological Constraints from Combining Photometric Galaxy Surveys and Gravitational Wave Observatories” by E.L. Gagnon, D. Anbajagane, J. Prat, C. Chang, and J. Frieman (all of U. Chicago, USA). This article quantifies the expected cosmological information gain from combining the forecast LSST 3x2pt analysis with the large-scale auto-correlation of GW sources from proposed next-generation GW experiments.

You can see the overlay here:

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

The third paper, also published on 10th December 2024, but in the folder marked Earth and Planetary Astrophysics, has the title “A potential exomoon from the predicted planet obliquity of β Pictoris b” and is written by Michael Poon, Hanno Rein, and Dang Pham all of the University of Toronto, Canada. It presents discussion, based on the β Pictoris system, of the idea that the presence of exomoons can excite misalignment between the spin and orbit axis (obliquity) in exoplanet systems

Here is the overlay

The final version accepted on arXiv is here.

Last of this quartet, published on 11th December 2024, and in the folder Cosmology and NonGalactic Astrophysics is “Map-level baryonification: Efficient modelling of higher-order correlations in the weak lensing and thermal Sunyaev-Zeldovich fields” and is by Dhayaa Anbajagane & Shivam Pandey (U. Chicago) and Chihway Chang (Columbia U.), all based in the 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, and that will probably be the last one of the year. If we publish just one more paper between now and 31st December, we will have published as many papers in 2024 as we have in all previous years put together!

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Cosmology Talks: Recent DESI Power Spectrum Results

Posted in The Universe and Stuff with tags , , , , , on December 12, 2024 by telescoper

Some weeks ago I posted an item about recent results that have emerged from the DESI (Dark Energy Spectroscopic Instrument) Collaboration. I have been a bit busy since then but I just saw that there is one of those Cosmology Talks about these results which I thought I would pass on. The contributors are Arnaud de Mattia, Hector Gil-Marín and Pauline Zarrouk and they are talking about the analsysis they have done using the “full shape” of the galaxy power spectrum. It’s quite a long video, but very illuminating.

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Four New Publications at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , on December 7, 2024 by telescoper

It’s Satuday morning once again so here’s another quick update of activity at the Open Journal of Astrophysics. Since the last update a week ago we have published  four papers, which takes the count in Volume 7 (2024) up to 110 and the total published altogether by OJAp up to 225.

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 “The impact of feedback on the evolution of gas density profiles from galaxies to clusters: a universal fitting formula from the Simba suite of simulations” by Daniele Sorini & Sownak Bose (Durham University, UK), Romeel Davé (University of Edinburgh, UK), and Daniel Anglés-Alcázar (University of Connecticut, USA). The paper, which is in the folder marked Astrophysics of Galaxies, presents a study of the effects of stellar and/or AGN feedback on the shape and evolution of gas density profiles in galaxy haloes using the SIMBA simulations. It was published on Tuesday 3rd December 2024.

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, also published on 3rd December 2024, and is also the folder “Astrophysics of Galaxies, is “Self-regulated growth of galaxy sizes along the star-forming main sequence” by Shweta Jain (U. Kentucky, USA), Sandro Tacchella (U. Cambridge, UK) and Moein Mosleh (Shiraz University, Iran).  This paper suggestes an identification of a possible self-regulating mechanism in galaxy size growth involving the interplay between feedback from star formation and newly accreted gas.

You can see the overlay here:

 

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

The third paper, published on Thursday 6th December 2024 in the folder marked Cosmology and NonGalactic Astrophysics, is called  “BLAST: Beyond Limber Angular power Spectra Toolkit. A fast and efficient algorithm for 3×2 pt analysis” by Sofia Chiarenza, Marco Bonici & Will Percival (Waterloo, Canada) and Martin White (Berkeley, USA). It presents BLAST, an efficient algorithm for calculating angular power spectra without employing the Limber approximation or assuming a scale-dependent growth rate, based on the use of Chebyshev polynomials. The code is written in Julia.

Here is the overlay

 

 

The final version accepted on arXiv is here.

Last in this batch, published on 6th December 2024, and in the folder Astrophysics of Galaxies, is “On the universality of star formation efficiency in galaxies” by Ava Polzin & Andrey V. Kravtsov (U. Chicago) and Vadim A. Semenov & Nickolay Y. Gnedin (CfA Harvard), all based in the USA. The paper presents an argument that the universality of observational estimates of star formation efficiency per free-fall time can be plausibly explained by the turbulence-driven and feedback-regulated properties of star-forming regions.

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

We seem to have recovered from a small Thanksgiving lull and, looking at the OJAp workflow, I think we’ll have a similar number of publications next week. I’ll do another update next weekend!

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Newton’s Opticks and a Query about the Bending of Light

Posted in History, The Universe and Stuff with tags , , , , on December 5, 2024 by telescoper

The story of the famous 1919 expeditions to measure the bending of light by the Sun as a test of general relativity has featured many times on this blog (e.g. here). I ahve also written elsewhere about it, e.g. here. One way this is often presented is whether the measurements preferred the “Einstein” prediction or one consistent with “Newton”, there being a famous factor of two between the two.

In fact the earliest published calculation of the deflection of light by the Sun was not by Isaac Newton but by Johann Georg von Soldner (Uber die Ablenkung eines Lichstrals von seiner geradlinigen Bewegung, durch die Attraktion eines Weltk¨orpers, and welchem er nahe vorbei geht. Berliner Astronomisches Jahrbuch, 1801: 161-172). This calculation does use Newtonian theory, but as far as I know there is no record tof any calculation of this sort by Newton himself.

There is, however, something very tantalizing in Newton’s 1704 book Opticks, published almost 20 years after his Principia outlined the laws of mechanics and of universal gravitation. Opticks which (unlike the Principia) was written in English, ends with a series of rhetorical questions called “Queries” which present speculative ideas about light and its interactions with matter. The first of these reads:

Query 1. Do not Bodies act upon Light at a distance, and by their action bend its Rays; and is not this action (caeteris paribus) strongest at the least distance?

This looks very much like a speculation about the bending of light by gravitation. But if that’s what it is, he could have done exactly what Soldner did about a century later. Why then did he never publish the result and why was it never found among his unpublished papers?

I’ve spoken to several people about this and there are three main ideas. One is that Newton actual did the Soldner calculation, and that the manuscript was accidentally destroyed in a fire caused by his dog, Diamond. The other is that he just never got round to it, which seems unlikely because it’s not a difficult calculation and Newton lived over 20 years after the publication of the Opticks. The third possibility is that Query 1 wasn’t about gravity at all. If it had been, wouldn’t he have used the word and wouldn’t he have mentioned the inverse-square law specifically? Perhaps what he had in mind was some kind of refraction. This interpretation is consistent with other Queries where he talks about the “aetherial Medium” through which he supposed light to propagate being distorted by the presence of massive bodies and thus causing refraction. For example, from Query 21,

Is not this Medium much rarer within the dense Bodies of the Sun, Stars, Planets and Comets, than in the empty celestial Spaces between them?

I suppose we’ll never know what Newton had in mind. I am split between the first and third explanations above.

It’s worth mentioning that some of the other Queries are very prescient. Take Query 5, for example:

Do not Bodies and Light act mutually upon one another; that is to say, Bodies upon Light in emitting, reflecting, refracting and inflecting it, and Light upon Bodies for heating them, and putting their parts into a vibrating motion wherein heat consists?

Clever chap, Newton!

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