Editing History of astronomy (section)

==Modern astronomy==
{{further|Astronomy|Observational astronomy|Physical cosmology#History of study}}

===19th century===
[[Image:Karte Mars Schiaparelli MKL1888.png|thumb|[[Mars]] surface map of [[Giovanni Schiaparelli]]]]

Pre-photography, data recording of astronomical data was limited by the human eye. In 1840, [[John W. Draper]], a chemist, created the earliest known astronomical photograph of the Moon. And by the late 19th century thousands of photographic plates of images of planets, stars, and galaxies were created. Most photography had lower quantum efficiency (i.e. captured less of the incident photons) than human eyes but had the advantage of long integration times (100 ms for the human eye compared to hours for photos). This vastly increased the data available to astronomers, which led to the rise of [[human computers]], famously the [[Harvard Computers]], to track and analyze the data.

Scientists began discovering forms of light which were invisible to the naked eye: [[X-ray]]s, [[gamma ray]]s, [[radio wave]]s, [[microwave]]s, [[ultraviolet radiation]], and [[infrared radiation]]. This had a major impact on astronomy, spawning the fields of [[infrared astronomy]], [[radio astronomy]], [[x-ray astronomy]] and finally [[gamma-ray astronomy]]. With the advent of [[spectroscopy]] it was proven that other stars were similar to the Sun, but with a range of [[temperature]]s, [[mass]]es and sizes.

The science of [[astronomical spectroscopy|stellar spectroscopy]] was pioneered by [[Joseph von Fraunhofer]] and [[Angelo Secchi]]. By comparing the spectra of stars such as [[Sirius]] to the Sun, they found differences in the strength and number of their [[spectral line|absorption lines]]—the dark lines in stellar spectra caused by the atmosphere's absorption of specific frequencies. In 1865, Secchi began classifying stars into [[stellar classification|spectral types]].<ref>{{cite web
 | last=MacDonnell | first=Joseph
 | url=http://www.faculty.fairfield.edu/jmac/sj/scientists/secchi.htm
 | archive-url=https://web.archive.org/web/20110721210124/http://www.faculty.fairfield.edu/jmac/sj/scientists/secchi.htm
 | archive-date=2011-07-21
 | title=Angelo Secchi, S.J. (1818–1878) the Father of Astrophysics
 | publisher=[[Fairfield University]]
 | access-date=2006-10-02}}</ref> The first evidence of helium was observed on August 18, 1868, as a bright yellow spectral line with a wavelength of 587.49 nanometers in the spectrum of the chromosphere of the Sun. The line was detected by French astronomer Jules Janssen during a total solar eclipse in Guntur, India.

The first direct measurement of the distance to a star ([[61 Cygni]] at 11.4 [[light-years]]) was made in 1838 by [[Friedrich Bessel]] using the [[parallax]] technique. Parallax measurements demonstrated the vast separation of the stars in the heavens.{{Citation needed|date=October 2021}} Observation of double stars gained increasing importance during the 19th century. In 1834, Friedrich Bessel observed changes in the proper motion of the star Sirius and inferred a hidden companion. [[Edward Charles Pickering|Edward Pickering]] discovered the first [[spectroscopic binary]] in 1899 when he observed the periodic splitting of the spectral lines of the star [[Mizar (star)|Mizar]] in a 104-day period. Detailed observations of many binary star systems were collected by astronomers such as [[Friedrich Georg Wilhelm von Struve]] and [[Sherburne Wesley Burnham|S. W. Burnham]], allowing the masses of stars to be determined from the computation of [[orbital elements]]. The first solution to the problem of deriving an orbit of binary stars from telescope observations was made by Felix Savary in 1827.<ref>{{cite book
 | first=Robert G. | last=Aitken | title=The Binary Stars | page=66
 | publisher=Dover Publications Inc. | location=New York
 | date=1964 | isbn=978-0-486-61102-0}}</ref>
In 1847, [[Maria Mitchell]] discovered a comet using a telescope.

===20th century===
[[File:Hubble 01 Cropped.jpg|thumb|The [[Hubble Space Telescope]]]]

With the accumulation of large sets of astronomical data, teams like the [[Harvard Computers]] rose in prominence which led to many female astronomers, previously relegated as assistants to male astronomers, gaining recognition in the field. The [[United States Naval Observatory]] (USNO) and other astronomy research institutions hired [[Human computer|human "computers"]],  who performed the tedious calculations while scientists performed research requiring more background knowledge.<ref>{{Cite web|url=http://maia.usno.navy.mil/women_history/history.html|archive-url=https://web.archive.org/web/20041030073611/http://maia.usno.navy.mil/women_history/history.html|url-status=dead|archive-date=October 30, 2004|title=history of women|date=October 30, 2004}}</ref> A number of discoveries in this period were originally noted by the women "computers" and reported to their supervisors. [[Henrietta Swan Leavitt]] discovered the [[cepheid variable]] star [[period-luminosity relation]] which she further developed into a method of measuring distance outside of the Solar System.

A veteran of the Harvard Computers, [[Annie Jump Cannon|Annie J. Cannon]] developed the modern version of the stellar classification scheme in during the early 1900s (O B A F G K M, based on color and temperature), manually classifying more stars in a lifetime than anyone else (around 350,000).<ref name="HubenyMihalas2014">{{cite book|author1=Ivan Hubeny|author2=Dimitri Mihalas|title=Theory of Stellar Atmospheres: An Introduction to Astrophysical Non-equilibrium Quantitative Spectroscopic Analysis|url=https://books.google.com/books?id=TmuYDwAAQBAJ&pg=PA23|date=26 October 2014|publisher=Princeton University Press|isbn=978-0-691-16329-1|pages=23}}</ref><ref>{{Cite web|url=https://scriptamus.wordpress.com/2009/12/14/ladies-of-the-laboratory-2-how-in-a-few-months-late-in-the-19th-century-one-man-who-had-little-interest-in-gender-equality-hired-more-female-astronomers-than-the-world-had-ever-known/|title=Ladies of the Laboratory 2: How in a Few Months Late in the 19th Century One Man Who Had Little Interest in Gender Equality Hired More Female Astronomers than the World Had Ever Known|date=December 14, 2009}}</ref>
The twentieth century saw increasingly rapid advances in the scientific study of stars.
[[Karl Schwarzschild]] discovered that the color of a star and, hence, its temperature, could be determined by comparing the [[visual magnitude]] against the [[photographic magnitude]]. The development of the [[Photoelectric effect|photoelectric]] [[photometer]] allowed precise measurements of magnitude at multiple wavelength intervals. In 1921 [[Albert A. Michelson]] made the first measurements of a stellar diameter using an [[interferometer]] on the [[Mount Wilson Observatory#100-inch Hooker telescope|Hooker telescope]] at [[Mount Wilson Observatory]].<ref>{{cite journal
 | last1=Michelson | first1=A. A. | last2=Pease | first2=F. G.
 | title=Measurement of the diameter of Alpha Orionis with the interferometer
 | journal=Astrophysical Journal | date=1921 | volume=53 | issue=5 | pages=249–259
 | bibcode=1921ApJ....53..249M | doi= 10.1086/142603 | pmid=16586823 | s2cid=21969744 | pmc=1084808}}</ref>

[[File:PIA16874-CobeWmapPlanckComparison-20130321.jpg|thumb|left|Comparison of [[CMB]] (Cosmic microwave background) results from satellites [[Cosmic Background Explorer|COBE]], [[WMAP]] and ''[[Planck (spacecraft)|Planck]]'' documenting a progress in 1989–2013]]
Important theoretical work on the physical structure of stars occurred during the first decades of the twentieth century. In 1913, the [[Hertzsprung–Russell diagram]] was developed, propelling the astrophysical study of stars.
In [[Potsdam]] in 1906, the Danish astronomer [[Ejnar Hertzsprung]] published the first plots of color versus [[luminosity]] for these stars. These plots showed a prominent and continuous sequence of stars, which he named the Main Sequence.
At [[Princeton University]], [[Henry Norris Russell]] plotted the spectral types of these stars against their absolute magnitude, and found that dwarf stars followed a distinct relationship. This allowed the real brightness of a dwarf star to be predicted with reasonable accuracy.
Successful [[Stellar model|models]] were developed to explain the interiors of stars and stellar evolution. [[Cecilia Payne-Gaposchkin]] first proposed that stars were made primarily of hydrogen and helium in her 1925 doctoral thesis.<ref>{{cite web
 |url        = http://cwp.library.ucla.edu/Phase2/Payne-Gaposchkin,_Cecilia_Helena@861234567.html
 |archive-url = https://web.archive.org/web/20050318221903/http://cwp.library.ucla.edu/Phase2/Payne-Gaposchkin,_Cecilia_Helena@861234567.html
 |url-status=dead
 |archive-date = 2005-03-18
 |title      = " Payne-Gaposchkin, Cecilia Helena." CWP
 |publisher  = [[University of California]]
 |access-date = 2013-02-21
}}</ref> The spectra of stars were further understood through advances in [[quantum mechanics|quantum physics]]. This allowed the chemical composition of the stellar atmosphere to be determined.<ref name="new cosmos">{{cite book
 | last1=Unsöld | first1=Albrecht | title=The New Cosmos
 | publisher=Springer | location=New York
 | date=2001 | edition=5th | pages=180–185, 215–216
 | isbn=978-3-540-67877-9}}</ref>
As evolutionary models of stars were developed during the 1930s, [[Bengt Strömgren]] introduced the term Hertzsprung–Russell diagram to denote a luminosity-spectral class diagram.
A refined scheme for [[stellar classification]] was published in 1943 by [[William Wilson Morgan]] and [[Philip Childs Keenan]].

[[File:Milky way map.png|thumb|upright=1.4|Map of the [[Milky Way]] Galaxy, with the [[constellations]] that cross the [[galactic plane]] in each direction and the known prominent components annotated including [[Spiral arm|main arms]], spurs, bar, [[Galactic Center|nucleus/bulge]], notable [[nebulae]] and [[globular clusters]]]]
The existence of our [[galaxy]], the [[Milky Way]], as a separate group of stars was only proven in the 20th century, along with the existence of "external" galaxies, and soon after, the expansion of the [[universe]] seen in the recession of most galaxies from us. The "[[Great Debate (astronomy)|Great Debate]]" between [[Harlow Shapley]] and [[Heber Curtis]], in the 1920s, concerned the nature of the Milky Way, spiral nebulae, and the dimensions of the universe.<ref>{{cite web
 |last1=Weaver
 |first1=H. F.
 |title=Robert Julius Trumpler
 |url=http://www.nap.edu/readingroom/books/biomems/rtrumpler.html
 |publisher=[[United States National Academy of Sciences|US National Academy of Sciences]]
 |access-date=January 5, 2007
 |archive-date=December 24, 2013
 |archive-url=https://web.archive.org/web/20131224112329/http://www.nap.edu/readingroom/books/biomems/rtrumpler.html
 |url-status=live
}}</ref>

With the advent of [[quantum physics]], [[spectroscopy]] was further refined.

The Sun was found to be part of a [[galaxy]] made up of more than 10<sup>10</sup> stars (10 billion stars). The existence of other galaxies, one of the matters of ''[[the great debate]]'', was settled by [[Edwin Hubble]], who identified the [[Andromeda Galaxy|Andromeda nebula]] as a different galaxy, and many others at large distances and receding, moving away from our galaxy.

[[Physical cosmology]], a discipline that has a large intersection with astronomy, made huge advances during the 20th century, with the model of the hot [[Big Bang]] heavily supported by the evidence provided by astronomy and physics, such as the [[redshift]]s of very distant galaxies and radio sources, the [[cosmic microwave background radiation]], [[Hubble's law]] and [[Big Bang nucleosynthesis|cosmological abundances of elements]].