An Etymological Dictionary of Astronomy and Astrophysics

The hypothesis first put forward by Immanuel Kant (1724-1804) according to which the objects termed “spiral nebulae” were stellar systems comparable to our own → Milky Way galaxy. At the end of the 18th century, William Herschel (1738-1822) using his giant reflectors discovered thousands of such nebulae. However, in spite of advances in observations it was never possible to prove Kant’s idea until the second decade of the twentieth century. The observations using the Mount Wilson 2.50m (100 inch)
telescope allowed Edwin Hubble in 1924 to firmly establish that the “spiral nebulae” were unquestionably extragalactic.

See also: The term “island Universe” was first introduced by the German Alexander von Humboldt in 1850; → island; → Universe.