100 years ago, Edwin Hubble proved our Milky Way galaxy isn't alone

Jan 17, 2025
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Another great scientist enjoying a pipe. Einstein was also a well-known pipe smoker. Always enjoy reading about the pioneers of space exploration in articles like this.
 
Sep 6, 2023
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Another great scientist enjoying a pipe. Einstein was also a well-known pipe smoker. Always enjoy reading about the pioneers of space exploration in articles like this.
I was going to say... I don't think I've ever seen a picture of Hubble without a pipe in his mouth!

It's interesting that Shapley had been at Mount Wilson when he did his work mentioned here (with the 60") but left about the time the 100" went into operation, to take over the directorship at Harvard Observatory. Otherwise he might have made the discovery Hubble is famous for.
 
Hubble, after attending Oxford, took up both the pipe and a British accent.

Hubble deserves the credit to finally ending the on-going debate regarding the "island universe" theory. But many scientists were convinced before his major work.

Here is my chronological work taken from several books that illustrate some of the great astronomy in the past:

1600s – Newton favored the idea of an infinite universe. This implies a universe that of homogeneity – stars and galaxies (perhaps) uniformly spread through the universe. Otherwise, to Newton’s view, the universe would collapse due to gravity.

1644 – Descartes published Principia Philosophiae. Universe has no center and is without limits, but argues that it is unwise to argue infinity but rater use indefinite instead.

1755 – Prussian journalist wrote that the nebulae may be their own “island universe” like the MW.

1763 – Alexander von Humboldt championed Kant’s disk-like galaxies, including the MW , and dubbed them “island universes”. This was “a phrase that would resonate throughout the astronomical community like a mantra…”

1786 – Herschel boasted he had discovered over 1500 new universes, but…

1790 – Herschel changed his view after discovering planetary nebulae.

1790’s – Kant and Laplace gave us the concept of these “island universes” since they appear to be comprised of stars.

1845 – The Earl of Rose, with his Leviathan telescope (6 ft. mirror), discovered that some nebulae were spiral.

1868 – William and Margaret Huggins used the shift in the spectral lines of Sirius to measure its speed (45 kps). [I present this because redshift measurements was strong evidence of other galaxies before Hubble’s great and more definitive work.]

1885 – A nova (SN) was observed in Andromeda, indicating that Andromeda could not be a distant island universe else the nova would be at least 50 million times the brightness of the Sun. This was beyond their comprehension.

1899 – Scheiner argues that M31 (Andromeda) is a galaxy like the MW. He had obtained a photo of the spectral lines of M31.
 
1908 – Henrietta Leavitt publishes 1,777 variables from the SMC and LMC. She further noted that there were 16 in the SMC stating, “It is worth of notice that…the burgher variables have the longer periods.” [Birth of Cepheid Variable astronomy]

1908 – Edward Fath confirmed Scheiner’s findings using the Crossley telescope at the Lick Obs. To him it was unmistakable – the Andromeda consists of a myriad of stars (i.e. a galaxy). He noted that the spectra of Andromeda was about the same as that of globular clusters – both spectra of stars, not nebulae. But he didn’t “push his findings”.

1910 – Hubble found clusters of what he thought might be galaxies. He suggests that if so, they would be millions of lightyears away.

1910 – Curtis, using the Crossley, discovers no rotation in spiral nebulae, when there should be unless, of course, they are extremely distant and large (ie galaxies).

Edington notes that this and other evidence, like apparent size and magnitude, only favors these spiral nebulae as galaxies.

Cambell, dir. of Lick Obs., agrees.

1912 – Puiseux, notes that long exposures reveal more and more spiral nebulae. He favored the view that they are like the MW.

1912 – Leavitt publishes her 25 Cepheids of the SMC. [But absolute distances to any Cepheid were still unknown.] Leavitt stated, “the logarithm of the period increases by about 0.48 for each increase of one magnitude in brightness”.

1912 – After being told by Lowell to study white nebulae (spirals), he improved his 450 lb. spectrograph by 200x!

1912 – Slipher measured, after long hours of exposure times, that Andromeda is moving at a rate of 300 kps towards us. [Modern day shows 301 kps.] This speed is about 10x that of stars in the MW, strongly suggesting Andromeda is extragalactic (ie galaxy).

1913 – Slipher publishes the first redshift measurements of spiral nebulae (galaxies). Later that year, he showed NGC 4594 had a redshift of 1000 kps.

1914 – Slipher had velocities for 14 spirals. The trend being for redshifts, not blueshifts. Hertzsprung writes Slipher in praise and noted that the results show them to be extragalactic, though Slipher was not pushing them as “island universes”.

1916 – Van Maannen (Mt. Wilson where Hubble worked) claimed that he found rotation in the spirals when comparing movements to older images. [This was, much later, debunked.]

[This claim was the primary reason, along with the nebulae-like appearances within spirals, that Shapley, who preceded Hubble, argued against the “island universe" model! It also meant that Hubble had to be bold enough to argue against his fellow colleague, but Hubble was able to acquire all the important data to do so.]
 
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1917 – Heber Curtis, using novae found in a spiral, found their distance to be far outside the MW. He further suggested, based on mag., that they are “of and order of 100 times as far away…”

1917 – Ritchey also found faint novae in spiral nebulae, suggesting distances in the millions of light years. He also noted that they number over 1 million.

1917 -- Slipher at the Am. Philosophical Society gave his report on 25 velocities, after getting his math checked by computer Elizabeth Williams in Boston. Slipher announced these observations were favorable to the “island universe” theory. Slipher also suggested the spirals might be “’scattering’ a precocious intimation of the cosmic expansion.”

1920 – Wolf (at Heidelberg) found a SN in NGC2608 in 1920, showing that it contained stars, thus extragalactic.

1920 – Cosmologies “Great Debate”. Curtis presented his work that the spirals were “island universes”. Shapley presented his view. [They never actually debated. 😉] And where was Hubble in this great presentation moment to favor a universe comprised of galaxies? *cough* [Hubble and Curtis did work with one another.]

Curtis stated…

1) Spirals displayed the spectra typical for collections of stars, not gas.

2) No spiral had ever been found in the MW.

3) Spirals seen away from the MW due to MW gas/dust blocking views.

4) Novae (not SN) were too faint to not be very far away.

5) Slipher great redshift velocities.

But Shapley also argued that the MW was large and Curtis that it wasn’t. So both had some good arguments.

1922 -- – Opik found, using radial redshifts for his assumed central mass, the distance to Andromeda to be 450 kpc.

1923 – Eddington published his Mathematical Theory of Relativity, 2nd edition in 1924, which included Slipher’s 41 radial velocities. It was reprinted many times and became a textbook. He included Slipher’s redshifts, thus entering mainstream science.

1923, Oct 4th – Hubble discovers a Cepheid in Andromeda. He estimates its distance to be 900k lyrs. [He was unaware that Cepheid come in two main flavors, and he used the wrong ones, hence is low distance estimate.]

1923 Dec – Hubble, using the brightest star method, measured distance of elliptical (like the LMC) to be 1 million lyrs.
 
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1924 – Hubble throughout the years found 12 Cepheids with periods ranging from 18 to 50 days. M33 brought him 22 Cepheids with similar periods. Yet, contrary to all his findings, he was too reluctant to publish due to his “sensitive ego”.

1924 Dec 23 – NYT reported that “…Dr. Hubbell (sic) Confirms View That They are ‘Island Universes’ Similar to Our Own.” Though Hubble had yet to go public.

1925 Jan 1 – Russell read Hubble’s paper at the AAS. 12 Cepheids in Andromeda, 22 in the Triangulum, giving both a distance of about 1 million lyrs. Hubble also noted that the 100” resolved the outer regions around these spirals into a vast collection of stars. James Jean used a different technique to confirm great distances, thus concluding Van Mannen’s rotations must go.

1925 – Slipher had 45 redshift velocities, mostly all from his work.

1925? – “There is not just one universe.” Hubble stated. “Countless whole worlds, each of them a mighty universe, are strewn all over the sky. Like the proverbial gains of sand on the beach are the universes, each of them peopled with billions of stars or solar systems. Science has already taken a census of nearly ten million galactic system or individual universes of stars.”

His talks became famous.

Shapley was tired of the various terms for these “universes”. Hubble preference was extragalactic nebulae. He adopted that they be termed galaxies. Hubble saw no need to abolish “venerable precedence”. It became the moniker only after Hubble’s death in 1952.
 
1925, Jan. 1 – AAS meeting in DC where Russell presented Hubble’s results of Cepheids in Andromeda and the Triangulum nebulae showing their distance using the 100” Mt. Wilson reflector. “had derived distance approaching one million light years for each, thus bringing confirmation to the so-called island universe theory.”

1925 – Lemaitre writes in 1950 that he had met with Slipher and Hubble, and recalls Hubble’s Washington announcement (by Russell sealing the deal on other galaxies). [The letter implies he heard Hubble give the news but Hubble stayed in CA.]

1927, June -- Lemaitre combined GR theory with the observations from Slipher and Hubble. He showed this to Einstein in the autumn of 1927 getting his negative result, same as the one he gave Friedmann. (p64) But his work was unnoticed until 1930. “Lemaitre is unequivocal, for the first time someone suggests and expanding universe.”

1928 July – Hubble made chair of the IAU Nebulae Comm. for the conference to be held in Leiden, southern Holland. Hubble was able to visit with de Sitter to discuss both cosmology and GR. De Sitter encouraged more redshift distance work since his model predicted the relationship. Slipher had gone as far as he could with his little 24” at Lowell. Hubble would work on finding the Cepheids and Humason, for hours, would image their redshift.

1929, Jan – Baade gave lecture stating that it was Curtis (Lick) and Ritchey (Mt. Wilson) who showed spirals as galaxies, using novae. He also stated that Hubble, with the 100”, improved their work with the use of Cepheid observations. He also stated that Wolf (Heidelberg) had found a SN in NGC2608 in 1920, proving it contained stars, thus extragalactic.

1929 – Hubble Ho estimate = 500 kps/Mpc

1929 – Hubble (distances) and Humason (redshifts) were found for 46 galaxies. He culled this to only 20 for accuracy. He found a linear relationship for speed and distance. [Lemaitre had already done this two years earlier, but Hubble would not have known, maybe, since no one seemed to notice. But Hubble may have never recognized this once it was later revealed.]

Author notes that Hubble never made any effort to acknowledge expansion
 
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