October 13th in History

October 13th54AD: Ageing Roman Emperor Claudius is poisoned to death under mysterious circumstances, possibly by his final wife Agrippina mother of Claudius' 17-year-old stepson Nero who would succeed him to the Roman throne.

1773 – Charles Messier Discovers the Whirlpool Galaxy On October 13, 1773, French astronomer Charles Messier discovered the first spiral galaxy.
He named it the "Whirlpool Galaxy".
Centuries later, scientists confirmed the spiral shape of our own Milky Way.
Today, the Whirlpool Galaxy is one of the most studied galaxies in the universe.

1884: The International Meridian Conference, held in Washington DC selects the Greenwich Meridian in London as the international standard for zero degrees longitude.

1963 The term Beatlemania was coined after The Beatles appeared at the Palladium. They made their debut as the top of the bill on ITV's 'Sunday Night at The London Palladium.'

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ElwoodBlues · M

Messier named the Whirlpool Galaxy M51. The optics of his era were unable to reveal its spiral structure; he classified it as a nebula.

Messier's overall project was spotting new comets. So he made a list of 110 objects that were diffuse and could be mistaken for comets but were not comets. So the famous Messier catalog was, to him, a "don't waste your time on these" list.

William Parsons labeled M51 the "Whirlpool" and classed it as a spiral nebula. The idea of different galaxies similar to our Milky Way began to be taken seriously and debated in the 1920s. Edwin Hubble, using the new 100 inch Hooker telescope, was able to identify Cepheid variable stars in the "Andromeda spiral nebula," thus proving it was a galaxy made of stars.

BTW, Cepheids have a periodicity proportional to their absolute brightness (magnitude), so if you can spot them you can measure their apparent magnitude and thereby determine their absolute distance. This enabled Hubble to show that Andromeda was much farther away than anything measured in the Milky Way.