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Today in #BeyondSolSys - the discovery of galaxies.
Through the 18th & 19th centuries, better telescopes revealed more nebulae - cloudy objects seen in the sky. Some were eventually seen to be made of resolved stars, others were not.
Through the 18th & 19th centuries, better telescopes revealed more nebulae - cloudy objects seen in the sky. Some were eventually seen to be made of resolved stars, others were not.
Visual spectroscopy (especially starting w/Wm and Margaret Huggins) showed some to be glowing gas clouds with emission spectra. (I tried this once using a similar telescope; took very keen eyes). But what of the rest?
Especially spiral nebulae? #BeyondSolSys
Especially spiral nebulae? #BeyondSolSys
Famously, spirals were found by observers w/Earl of Rosse's 1.8m Leviathan of Parsonstown in Ireland. This 1862 drawing of Messier 51 from Paris stacks up very well against CCD images, especially since early observers didn't "know" what they should see. #BeyondSolSys
As photography took over, 1000s of spiral nebulae (+in hindsight, elliptical ones) came in range. Especially Curtis' studies w/ @LickObservatory 0.9m Crossley telescope became famous, showing dusty disks before it was clear what spirals were. #BeyondSolSys
Early 20th century: main ideas were:
- planetary systems in formation, looking like Kant's nebular hypothesis in action
- "island Universes", independent systems like our (then-unfolding view of) Milky Way galaxy.
2 people using same telescope were testing these. #BeyondSolSys
- planetary systems in formation, looking like Kant's nebular hypothesis in action
- "island Universes", independent systems like our (then-unfolding view of) Milky Way galaxy.
2 people using same telescope were testing these. #BeyondSolSys
At Mt Wilson 2.5m scope, then largest in world:
Adriaan van Maanen tested protoplanetary disk idea, by watching for rotation of spirals over spans of years. Would learn rotation periods; and if he saw nonzero signal, they must be too close to be separate galaxies. #BeyondSolSys
Adriaan van Maanen tested protoplanetary disk idea, by watching for rotation of spirals over spans of years. Would learn rotation periods; and if he saw nonzero signal, they must be too close to be separate galaxies. #BeyondSolSys
van Maanen reported unwinding rotation patterns (example: M33). Kind of a longstanding history-of-science problem why - he literally wrote the book on protocols to avoid expectation bias. (Irony - @ESAGaia can now measure rotn of M31, LMC, SMC) #BeyondSolSys
Meanwhile, using the same telescope, Edwin Hubble tested the island-Universe idea by looking for Cepheid variable stars in spiral/irregular nebulae appearing largest (so expected to be nearest). Photos showed tiny dots - but were they really stars? #BeyondSolSys
We now know how that turned out - he found them in numbers. The magic is that Cepheids have a close correlation between pulsation period (measured once you have data to show it's a Cepheid) and average luminosity (the Leavitt law). #BeyondSolSy
Edwin Hubble (too confusing to just say Hubble) thus demonstrated separate stellar systems comparable to Milky Way (so plural "galaxies" makes sense). Goal of extending Cepheid distance data past 60 million light-years was one reason for naming of @NASAHubble. #BeyondSolSys
He also left other important results often bearing his name:
Hubble-Lemaitre law for galaxy redshifts, and
Hubble classification system for galaxy structures.
#BeyondSolSys
Hubble-Lemaitre law for galaxy redshifts, and
Hubble classification system for galaxy structures.
#BeyondSolSys
