Appendix: The Discovery of Galaxies

Don't Panic

File: Galaxies file: galaxy_discovery_appendix.html.
Sections:
  1. Introduction
  2. Appendix: The History of the Discovery of Galaxies
  3. Appendix: Edwin Hubble

  1. Introduction

    2. This Galaxies file: galaxy_discovery_appendix.html is an appendix to IAL 26: The Discovery of Galaxies.

    It gives a bit more detail about the about the the discovery of galaxies per se and Edwin Hubble (1889--1953) role in the discovery of galaxies.

    The figure above (local link / general link: galaxy_hcg_87.html) and figure below (local link / general link: galaxy_hcg_87.html) of a Hickson Compact Group of galaxies is a preview for galaxies in general.

  2. Appendix: The History of the Discovery of Galaxies

    3. Given below are some figures that form a useful appendix to the the history of discovery of galaxies (discussed above in section The Discovery of Galaxies: An Example of the Process of the Scientific Method).

    1. Simon Marius and the Discovery of the Andromeda Nebula:

      Simon Marius (1573--1625) independently (but NOT firstly) and telescopically (firstly) discovered Andromeda nebula (i.e., the Andromeda Galaxy (M31,NGC 224)) on 1612 Dec15 (Wikipedia: Simon Marius: Discoveries; Wikipedia: Andromeda Galaxy: Observation history; SEDS: Simon Marius (January 20, 1573 - December 26, 1624); No-402). His discovery was, of course, for a long time the effective discovery relative to Europe.

      For more on Simon Marius (1573--1625), see the figure below local link / general link: simon_marius.html.

    2. Early Speculations on the Nature of the Nebulae: Redux:

      Recall the first persons in the 18th century to speculate that nebulae (historical usage) were other galaxies (after Emanuel Swedenborg (1688--1772)) were Thomas Wright (1711--1786) Immanuel Kant (1724--1804), and Heinrich Lambert (1728--1777). For a cartoon of them, see the figure below (local link / general link: alien_galaxooges.html).

    3. William Herschel (1738--1822): Redux:

      For more on William Herschel (1738--1822), see the figure below (local link / general link: william_herschel.html).

    4. Lord Rosse (1800-1867): Redux:

      For William Parsons, Lord Rosse, formally 3rd Earl of Rosse (1800-1867) see the figure below (local link / general link: lord_rosse.html).

      Lord Rosse made sketches of some spiral nebulae. We showed one of the Whirlpool Galaxy (AKA M51a/NGC 5194 and M51b/NGC 5195) above in subsection The Spiral Nebulae. See the figure below (local link / general link: galaxy_whirlpool.html) for two modern images of M51---which shows Lord Rosse did NOT do too badly.

  3. Appendix: Edwin Hubble

    4. We here expand a bit on what was said about Edwin Hubble (1889--1953) in the above section The Discovery of Galaxies: An Example of the Process of the Scientific Method.

    1. The Life of Hubble:

      Edwin Hubble (1889--1953) came from Missouri---but nevertheless took a law degree from Oxford and practiced law in Kentucky before leaving all that to do a Ph.D. in astronomy (1917) (No-508). See images of Edwin Hubble in the figure below (local link / general link: edwin_hubble.html).

      Hubble was also an athlete and is the only known astronomer to have boxed a world light heavyweight champion: Georges Carpentier (1894--1975)---a non-title bout one assumes (No-508).

      After serving in the infantry in WWI, he joined the staff of Mount Wilson Observatory in southern California in 1919 (No-509).

      Ah, California: see the figure below (local link / general link: pfeiffer_beach.html).

      Hubble, remarkably for an astronomer, became a well known person in Hollywood during its golden age and he possibly turns up in small parts in Hollywood novels under different names: e.g., maybe in James Hilton's (1900--1954) Morning Journey (1951).

    2. Observing Advantages:

      The great discoveries Hubble was to make at Mount Wilson Observatory in California (see also Mount Wilson Observatory page ) were predicated on the facts that Mount Wilson Observatory in those days (the 1920s) was one of the best observing sites in the world---this was before the smog and the light pollution of Los Angeles mostly ruined things---and on having the largest telescope to date at his disposal: the Hooker telescope (reflector, primary diameter 2.54 m = 100 in, operational 1917--present): see figure below (local link / general link: telescope_hooker.html).

    3. Hubble and the Nebulae:

      Hubble from his Ph.D. student days had been interested those nebulae (historical usage) that we now classify as galaxies: i.e., the spiral nebulae and elliptical nebulae (No-508).

      He had developed what we now call the Hubble sequence galaxy types by 1923 (No-508--509) which is illustrated in the Hubble tuning-fork diagram: the figure below (local link / general link: galaxy_hubble_sequence.html).

      Recall, we discussed galaxy types above in subsection Types of Galaxies and a fuller discussion of galaxy morphological classification is given in IAL 28: Galaxies: Types of Galaxies.

    4. The Andromeda Galaxy and Cepheids:

      In the early 1920s using the 100-inch Hooker telescope, Hubble was able to resolve stars in the outer regions of the Andromeda nebula (M31) (which is now known as the Andromeda Galaxy) and the Triangulum nebula (M33) (which is now known as the Triagulum Galaxy) by 1923 (No-509).

      These galaxies are in Local Group of Galaxies which is shown in the figure below (local link / general link: local_group.html).

      The fact that Hubble could resolve stars in the Andromeda nebula (M31) and the Triangulum nebula (M33), just in itself, proved that spiral nebulae were NOT just whirlpools of gas in space---though they could still have some gas, of course---as indeed they do.

      The       Andromeda Galaxy is shown up close in the figure below (local link / general link: galaxy_andromeda_m31.html).

      In the       Andromeda nebula, Hubble found that 34 stars were Cepheids by identifying their the known period-luminosity relation (No-510).

      By 1924 using the approximately known luminosities of Cepheids and period-luminosity relation, he was able to put the Andromeda nebula at 285 kpc No-510 well beyond the confines of the Milky Way (size scale ∼100 kpc as established by Harlow Shapley (1885--1972) in 1916 by determining the distances to Milky Way globular clusters also using Cepheids (see Wikipedia: Edwin Hubble: Universe goes beyond the Milky Way galaxy; No-493,510).

      Recall, Cepheids are very luminous post-main-sequence stars that are used as distance indicators. Cepheids are explicated in the figure below (local link / general link: star_hr_cepheids.html).

      From his observations of       Cepheids in the Andromeda nebula, Hubble had discovered that said Andromeda nebula was, in fact, the Andromeda Galaxy (M31), a giant system well outside of the Milky Way---see the figure below (local link / general link: alien_hubble.html).

      By the       1924, Hubble had established the distance to the Andromeda Galaxy (M31) to be 285 kpc (No-510).

      This is NOT a very accurate result. Hubble had various systematic errors in his measurements and calibrations that are entirely understandable given his time.

      The modern distance to the Andromeda Galaxy (M31) is 765 kpc (Wikipedia: Andromeda Galaxy): this ∼ 2.7 times Hubble's value.

      But even if Hubble's contemporaries suspected large errors---and they may have---they did concede fairly soon ??? that the Andromeda Galaxy (M31) had to be a remote large system of stars comparable in size to Milky Way.

    5. Wild Extrapolation:

      Now if Andromeda Galaxy (M31) is another galaxy comparable in size to Milky Way, then:

      1. All the spiral nebulae were spiral galaxies too---and NOT little gas/dust whirlwinds inside the Milky Way. And there were thousands of spiral galaxies extending out as far as the Hooker telescope (reflector, primary diameter 2.54 m = 100 in, operational 1917--present) could see.

      2. Also other nebulae (historical usage) with star-like spectra, which could be found in systems with spiral nebulae (i.e., elliptical nebulae, lenticular nebulae, and irregular nebulae), were also all other galaxies.

      3. The Milky Way (which was recognized as being disk-like since the 18th century at least) was also probably a spiral galaxy. Its spiral structure would NOT be proven until hydrogen 21-centimeter line observations in the radio band fiducial range 3 Hz -- 300 GHz = 0.3 THz, 0.1 cm -- 10**5 km started to become available after World War II (1939--1945).

      For an elliptical nebulae that must be a galaxiy since it is found in the Virgo Cluster (of galaxies), see M87 in the figure below (local link / general link: m87_virgo_old_image.html).

      For more on       Edwin Hubble (1889--1953), see Edwin Hubble (1889--1953) videos below (local link / general link: edwin_hubble_videos.html).

        EOF

    File: Galaxies file: galaxy_discovery_appendix.html.