Back in the past, was the sun assumed to be at rest in the luminous aether frame?

  • $\begingroup$ How long ago is "was", please? In any case, what research have you done? For much of history, the Sun was assumed to be moving round the Earth… not "at rest" in any frame. For a little while, the Sun was taken to be a body at rest, with all else in the solar system rotating around it. In recent centuries, the Sun has been clearly seen as moving with respect to everything else and still, apparently, the resting point around which all else in the system rotates. Which works for you? $\endgroup$ – Robbie Goodwin Feb 25 at 21:39

Not necessarily. They did not know the velocity of the Sun with respect to aether. What they tried to do is to measure the speed of the Earth with respect to aether. If any velocity were detected, one could infer the speed of the Sun. But no speed was detected. And the idea that the Earth is at rest while everything else moves looked absolutely implausible in 19th century.

  • $\begingroup$ Hi Sir Alexandre, My textbook Kleppner, uses the value of $v$ , the average orbital speed of Earth round the sun as the speed of Earth thorough ether in the Michelson morley experiment. So I think back then they thought that the sun might be at rest in the ether. $\endgroup$ – Kashmiri Feb 25 at 14:41
  • $\begingroup$ Does the author of that textbook have a historical note about that calculation? I suspect not. Just because they do the calculation that way in that specific textbook (i.e. assume the Sun is at rest w.r.t. the aether), does not imply that is how the calculation was done "in the past." $\endgroup$ – Daddy Kropotkin Feb 25 at 21:49
  • $\begingroup$ The book is highly reputable from MIT, Although they have not added much historical notes about it. That made me ask this question. $\endgroup$ – Kashmiri Feb 26 at 4:25

Short Answer:

19th centry astronomers believed that the Sun and the Solar System revolved around the central point of the Milky Way Galaxy. Thus 19th centry physicists should have believed that the Sun moved with respect to the aether.

Long Answer:

By the beginning of the 19th century, astronomers were certain that the Sun was a star in the Milky Way Galaxy, which most astronomers assumed was the entire universe, though there were speculations that other galaxies might exist beyond the Milky Way.

According to Newton's law of gravity all objects in the Milky Way Galaxy must revolve around the barycenter, the mathematical center of mass, of the Milky Way Galaxy.

Star Names: Their Lore and Meaning Richard Hincley Allen, 1899, 1963, The section on constellation Hercules - star Lambda Heruclis says:

Athough Johann Tobias Mayer of Gottingen seems to have been the pioneer, in 1760, in the efforts to ascertain the direction of the sun's movement among the stars, yet Sir William Herschell was thes first successful investigator as to this, about 1806, and he settled upon the vicinity of Lambda as the objective point of our solar system, the Apex of the Sun's Way; and his determination was, in a great measure, confirmed by later astronomers.

And Wikpedia says:

In 1783, English-German astronomer William Herschel described the solar apex, the point in sky towards which the Solar System is moving; using data from double stars, he identified this position as close to Lambda Herculis. Today it is known the solar apex is not so close to this star, however it is only 10° away from the position currently accepted (in Hercules, southwest of Vega).[14][15][16]


Astronomers knew that the distances between one star and its nearest neighbor must be immense, to say nothing of the distance from one one edge of the Milky Way Galaxy accross the center point to the opposite edge. But they didn't know what the scale of interstellar space was until the distances to three stars were measured in the late 1830s and the distances to several more were measured in following decades.

I happen to own an astronomy book written by Ormsby M. Mitchell (1810-1862),The Planetary and Stellar Worlds, 1851.


Lecture X the Motions and Revolutions of the Fixed Stars, pages 318-319, describes Madler's theory that Alcyone in the Pleiades star cluster is the central sun at the center of gravity of the Milky Way Galaxy (then assumed to be the entire universe).

After a profund examination, Madler reached the conclusion that Alcyone, the principal star in the group of the Pleiades, now occupies the centre of gravity, and is at present the sun about which the universe of stars comprising our central system are all revolving.

Star Names: Their Lore and Meaning Richard Hincley Allen, 1899, 1963, the section on Canis Major - Sirius says:

The celebrated Kant thught that Sirius was the central sun of the Milky Way;...

If Sirus was the central sun, other stars would revolve around it. Emmanuel Kant lived from 1724 to 1804.

Star Names: Their Lore and Meaning Richard Hincley Allen, 1899, 1963, the section on Taurus - The Pleidades - Alcyone says:

Madler located in Alcyone the center of the universe, but his theory has been shown to be fallacius. There is no satisfactory reason for his conclusions, and little more for Miss Clerke's remarks about the probable size and distance of Alcyone,--that it shines to its fellow stars with a luster eighty three times that of Sirius in terrestrial skies, while its intrinsic briliancy, as compared with that of the sun is 1000 times greater. All this rests upon the extremely doubtful assumption of a parallax of 0".013 deduced from the star's proper motion.

If Alcyone was in the center of the universe all the other stars would have to revolve around it.

Actually Alcyone is even farther than Miss Clerke said, since it now listed as having about 2,400 times the luminosity of the Sun.


At the present time the Sun is believed to orbit the gravitational center of the Milky Way Galaxy in a roughly circular orbit at a distance of about 27,140 plus or minus 460 light years from the central point.

It takes the Solar System about 240 million years to complete one orbit of the Milky Way (a galactic year),[16] so the Sun is thought to have completed 18–20 orbits during its lifetime and 1/1250 of a revolution since the origin of humans.


If the Sun has an perfectly circular orbit of exactly 27,140 light years radius, and thus exactly 185,415.052 light years circumference, and it takes exactly 240,000,000 years to make one orbit, the line between the Sun and the center of the Galaxy would change its angle very slightly during any time period which is understandable by humans.

There are 360 degrees of arc in a full circle, so it would take 666,666.666 years for the angle to the Sun to move by one degree as seen from the galaxtic center.

There are 60 minutes of arc in a degree, so it would take 11,111.1111 years for the angle to the Sun to move by one minute as seen from the galactic center.

There are 60 seconds of arc in a minute of arc, so it would take 185.185 years for the angle to the Sun to move by one second as seen from the galactic center.

In Edgar Allan Poe's story "Mellonta Tauta" (1849), a journel written in the year 2848, it is said:

April 6.—Last night had a fine view of Alpha Lyrae, whose disk, through our captain's spy-glass, subtends an angle of half a degree, looking very much as our sun does to the naked eye on a misty day. Alpha Lyrae, although so very much larger than our sun, by the by, resembles him closely as regards its spots, its atmosphere, and in many other particulars. It is only within the last century, Pundit tells me, that the binary relation existing between these two orbs began even to be suspected. The evident motion of our system in the heavens was (strange to say!) referred to an orbit about a prodigious star in the centre of the galaxy. About this star, or at all events about a centre of gravity common to all the globes of the Milky Way and supposed to be near Alcyone in the Pleiades, every one of these globes was declared to be revolving, our own performing the circuit in a period of 117,000,000 of years! We, with our present lights, our vast telescopic improvements, and so forth, of course find it difficult to comprehend the ground of an idea such as this. Its first propagator was one Mudler. He was led, we must presume, to this wild hypothesis by mere analogy in the first instance; but, this being the case, he should have at least adhered to analogy in its development. A great central orb was, in fact, suggested; so far Mudler was consistent. This central orb, however, dynamically, should have been greater than all its surrounding orbs taken together. The question might then have been asked—"Why do we not see it?"- we, especially, who occupy the mid region of the cluster—the very locality near which, at least, must be situated this inconceivable central sun. The astronomer, perhaps, at this point, took refuge in the suggestion of non-luminosity; and here analogy was suddenly let fall. But even admitting the central orb non-luminous, how did he manage to explain its failure to be rendered visible by the incalculable host of glorious suns glaring in all directions about it? No doubt what he finally maintained was merely a centre of gravity common to all the revolving orbs—but here again analogy must have been let fall. Our system revolves, it is true, about a common centre of gravity, but it does this in connection with and in consequence of a material sun whose mass more than counterbalances the rest of the system. The mathematical circle is a curve composed of an infinity of straight lines; but this idea of the circle—this idea of it which, in regard to all earthly geometry, we consider as merely the mathematical, in contradistinction from the practical, idea—is, in sober fact, the practical conception which alone we have any right to entertain in respect to those Titanic circles with which we have to deal, at least in fancy, when we suppose our system, with its fellows, revolving about a point in the centre of the galaxy. Let the most vigorous of human imaginations but attempt to take a single step toward the comprehension of a circuit so unutterable! I would scarcely be paradoxical to say that a flash of lightning itself, travelling forever upon the circumference of this inconceivable circle, would still forever be travelling in a straight line. That the path of our sun along such a circumference—that the direction of our system in such an orbit—would, to any human perception, deviate in the slightest degree from a straight line even in a million of years, is a proposition not to be entertained; and yet these ancient astronomers were absolutely cajoled, it appears, into believing that a decisive curvature had become apparent during the brief period of their astronomical history—during the mere point—during the utter nothingness of two or three thousand years! How incomprehensible, that considerations such as this did not at once indicate to them the true state of affairs—that of the binary revolution of our sun and Alpha Lyrae around a common centre of gravity!


Poe also wrote similarly about the Sun's orbit in his 1848 essay Eureka: a Prose Poem.


I note that if it took the Sun 117,000,000 years to make a complete circle, it would take it 325,000 years for its path to curve by a degree, and 5,416.666 years for its path to curve by an arc minute, and 90.2777 years for its path to curve by one arc second. Astronomers could already measure angles of an arc second or smaller in Poe's era. So the claim that the curvature of the Sun's path would undetectable after a million years is false - a circular orbit taking 117,00,000 years would curve by 3.076 degrees in a million years.

Anyway, I read many Poe stories, including "Mellonta Tauta," when I was 11 or 12. So if someone asked me about the subject when I was 12 years old, I could have told them that 19th century astronomers believed that the Sun orbited around the center of the galaxy, and thus 19th century physicists should have believed that the Sun moved with respect to the aether.

  • $\begingroup$ The Milky Way wasn't thought to be rotating until 1904, so I highly doubt the first sentence of your short answer is correct. $\endgroup$ – Spencer Feb 27 at 23:56
  • $\begingroup$ @Spencer It is possible that astronomers didn't detect rotation of the Milky Way as a whole until 1904. But they certainly knew that each individual star had to revolve around the center of the Milky Way. Perhaps you should read my entire long answer and the quotations within it. $\endgroup$ – M.A. Golding Mar 7 at 20:47

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