Extra-Galactic Nebulae by Edwin Hubble

Born #onthisday in 1889, Edwin Hubble was an American astronomer who played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology.

Hubble proved that many objects previously thought to be clouds of dust and gas and classified as "nebulae" were actually galaxies beyond the Milky Way. He used the strong direct relationship between a classical Cepheid variable's luminosity and pulsation period (discovered in 1908 by Henrietta Swan Leavitt [2]) for scaling galactic and extragalactic distances.

Hubble also discovered Hubble's law (aka the Hubble–Lemaître law), which is the observation that galaxies are moving away from Earth at speeds proportional to their distance. Said another way, the farther away a galaxy is, the faster it is moving away. The velocity of the galaxies has been determined by their redshift, a shift of the light they emit toward the red end of the visible spectrum [4].

Hubble's law is considered the first observational basis for the expansion of the universe, and today it serves as one of the pieces of evidence most often cited in support of the Big Bang model [5].

[Image credit: https://www.space.com/]

References
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[1] "Edwin Hubble", https://en.wikipedia.org/wiki/Edwin_Hubble

[2] "Henrietta Leavitt – Celebrating the Forgotten Astronomer", https://www.aavso.org/henrietta-leavitt-%E2%80%93-celebrating-forgotten-astronomer

[3] "Extra-galactic nebulae", https://www.gutenberg.org/ebooks/68428

[4] "Hubble's law", https://en.wikipedia.org/wiki/Hubble's_law

[5] "Hubble’s Law and the expanding universe", https://www.pnas.org/doi/10.1073/pnas.1424299112

#hubble #space #galaxies #universe #astronomy