Edwin Hubble announced #OTD in 1925 that Andromeda and other spiral nebulae were in fact separate galaxies outside the Milky Way, in a paper read to an AAS meeting by H.N. Russell.
The Universe was more than just our little island of stars, far greater in extent than what many astronomers had allowed themselves to imagine.
Hubble built on observations by Vesto Slipher, collaborated with Milton Humason, and relied on Henrietta Swan Leavitt’s work on Cepheid variables to reach this conclusion.
It seems hard to believe, but there are people alive today who were born into what scientists thought was a much smaller universe.
Former US President Jimmy Carter was three months old when Hubble made his announcement.
Betty White, who passed away just over a year ago, was always my favorite example of this. She was about to turn three years old.
Hubble’s announcement — Other galaxies exist! Our Milky Way is just one in a Universe full of them! — was made on the third day of the 33rd Meeting of the American Astronomical Society, in a paper read by H.N. Russell. The meeting started on December 30th; I don’t know if Hubble waited for New Year’s Day to be dramatic.
For astronomers, the announcement probably wasn’t a sudden revelation. Hubble had been discussing this result with colleagues, and word had gotten around.
It’s hard to imagine the pre-Hubble view of the Universe, though it was less than 100 years ago.
Just a year before Hubble’s announcement, many astronomers thought the collection of stars that make up our galaxy was… Everything.
Astronomer Harlow Shapley was perhaps the leading proponent of the establishment view. He had long argued that spiral nebulae seen by astronomers — shapes any kid would now recognize as galaxies — were just dust clouds inside the Milky Way.
Images: Huntington Library
It was the identification of Cepheid variable stars in M31 and other spiral nebulae that allowed Hubble to prove they were so far away that they must be outside the Milky Way.
A Cepheid variable is a type of star whose brightness waxes and wanes over a period of time that tightly correlates with its maximum brightness.
Measure that period and you know its absolute brightness. Compare that to how bright it appears, and you can estimate its distance.
This important property of Cepheid variable stars was discovered by astronomer Henrietta Swan Leavitt. It makes them “standard candles” (a term she coined) that we can reliably use for establishing distances to cosmologically nearby galaxies.
Henrietta Swan Leavitt’s period-luminosity relationship for Cepheids is one of the first rungs on the “cosmic distance ladder,” the collection of methods used by astronomers to measure extragalactic distances.
In the early morning hours of October 6, 1923, Edwin Hubble took a photo plate of M31 showing a Cepheid variable star. He originally mistook it for a nova - you can see where he has crossed out an “N” on the plate and excitedly replaced it with “VAR!”
Applying Henrietta Swan Leavitt’s period-luminosity relationship to subsequent observations, Hubble concluded that the distance to M31 was greater than reliable size estimates for the Milky Way.
Image: Carnegie Observatories
Hubble kept Shapley in the loop as he built the case for separate galaxies throughout 1924, alerting him to the discovery of Cepheid variables in M31, M33, and other spiral nebulae.
Shapley, who had long argued that the Milky Way was the whole Universe, doubted Hubble at first. But he eventually relented in the face of growing evidence.
Upon receiving one of Hubble's letters, Shapley remarked to doctoral student Cecilia Payne-Gaposchkin “Here is the letter that destroyed my universe.”
Astronomically, January 1st is a meaningless date. It is an arbitrary reference point in a system based on the approximate orbital period of an otherwise unremarkable star that is perhaps only notable for having a life-bearing planet.
But for those of us who reckon time by this system, today is the 98th anniversary of humanity taking a monumental step towards understanding our place in a Universe that is vast and puzzling, but ultimately knowable.
Happy New Year!
Image: Richard Powell
The New Year, while basically a religious festival, has so much history behind it, because it is related to the creation and adaption of the Gregorian calendar. When the early Romans had devised their calendar, there were only 10 months, with March being the first
Y'know what yeah we really should. That along with a 13-month 28-day calendar (with year and leap days that don't count) is the way to go.
You left out the best part (imho): In which Hubble's insanely huge universe turns out to be TOO SMALL.
That is, because he was unaware of the 2 kinds of Cepheid variables, his distance/universe-size estimates were off by a factor of 10.
... which put the age of the universe at ~1 billion years, ... this being roughly when geologists, in their initial attempts to get the age of the Earth came up with ~5 billion years
... a mystery that took another decade or so to resolve.
@mcnees Wild to think we've known about galaxies for less than a century. Makes me think about how much we still don't understand the universe, and wonder what the next astronomical paradigm shift will be.
Fingers crossed that it's "dark matter is consciousness / souls / gods / the rest of the multiverse / a source of unlimited free energy / all the lost socks [choose 2]"
@mcnees
I'd love to see a movie series giving us a view into the lives of undersung #WomenAstronomers of the past, like Caroline Herschel, Henrietta Swan Leavitt, Celilia Payne-Gopaschkin, and many others. All I've ever seen is brief narratives of some.
Newton said he saw further than others because he stood on the shoulders of giants (tho I've read he was being sarcastic.) But it's true for all scientists, and many of those shoulders belonged to women, most we never have heard much about.
Robert McNees
Denise Pouchet
Enema Cowboy
Martin Vermeer (not Jesus)
Auran 🏳️⚧️🐰
Ted Spence
Roger Crew✅❌☑🗸❎✖✓✔
Karsten™️
Peter Coles 🏳️🌈 🏳️⚧️
Jennifer Rittenhouse West
Stargeezer Smith
Tonydunc
Richard Easther
Level 98 🇺🇦