Editing Solar mass (section)

== History of measurement ==
The value of the gravitational constant was first derived from measurements that were made by [[Henry Cavendish]] in 1798 with a [[torsion balance]].<ref>{{cite web |url=http://www.phys.utk.edu/labs/modphys/Pasco%20Cavendish%20Experiment.pdf |title=Universal Gravitational Constant |pages=13 |access-date=11 April 2019 |work=[[University of Tennessee]] Physics |first=Geoffrey R. |last=Clarion |publisher=PASCO}}</ref> The value he obtained differs by only 1% from the modern value, but was not as precise.<ref>{{cite book
|author=Holton, Gerald James |author2=Brush, Stephen G.
| title=Physics, the human adventure: from Copernicus to Einstein and beyond
| date=2001 | page=137 | edition=3rd
| publisher=[[Rutgers University Press]]
| isbn=978-0-8135-2908-0}}</ref> The [[parallax#Diurnal parallax|diurnal parallax]] of the Sun was accurately measured during the transits of Venus in 1761 and 1769,<ref>{{cite book
| author=Pecker, Jean Claude| author2=Kaufman, Susan
| title=Understanding the heavens: thirty centuries of astronomical ideas from ancient thinking to modern cosmology | pages=291 | publisher=Springer
| date=2001 | isbn=978-3-540-63198-9| bibcode=2001uhtc.book.....P
}}</ref> yielding a value of {{val|9|u=arcsecond}} (9&nbsp;[[Minute and second of arc|arcsecond]]s, compared to the present value of {{val|8.794148|u=arcsecond}}). From the value of the diurnal parallax, one can determine the distance to the Sun from the geometry of Earth.<ref>{{cite book
| first=Cesare | last=Barbieri | date=2007
| title=Fundamentals of astronomy
| pages=132–140 | publisher=[[CRC Press]]
| isbn=978-0-7503-0886-1}}</ref><ref>{{Cite web|title=How do scientists measure or calculate the weight of a planet?|url=https://www.scientificamerican.com/article/how-do-scientists-measure/|access-date=2020-09-01|website=Scientific American|language=en}}</ref>

The first known estimate of the solar mass was by [[Isaac Newton]].<ref>{{cite journal |title=Newton's Determination of the Masses and Densities of the Sun, Jupiter, Saturn, and the Earth |first=I. Bernard |last=Cohen |s2cid=122869257 |author-link=I. Bernard Cohen |journal=[[Archive for History of Exact Sciences]] |volume=53 |issue=1 |pages=83–95 |date=May 1998 |jstor=41134054 |doi=10.1007/s004070050022 |bibcode=1998AHES...53...83C }}</ref> In his work ''[[Philosophiæ Naturalis Principia Mathematica|Principia]]'' (1687), he estimated that the ratio of the mass of Earth to the Sun was about {{frac|{{val|28700}}}}. Later he determined that his value was based upon a faulty value for the solar parallax, which he had used to estimate the distance to the Sun. He corrected his estimated ratio to {{frac|{{val|169282}}}} in the third edition of the ''Principia''. The current value for the solar parallax is smaller still, yielding an estimated mass ratio of {{frac|{{val|332946}}}}.<ref>
{{cite book
| first=David | last=Leverington | date=2003
| title=Babylon to Voyager and beyond: a history of planetary astronomy
| page=126 | publisher=[[Cambridge University Press]]
| isbn=978-0-521-80840-8
}}</ref>

As a unit of measurement, the solar mass came into use before the AU and the gravitational constant were precisely measured. This is because the relative mass of another planet in the [[Solar System]] or the combined mass of two [[binary star#Use in astrophysics|binary stars]] can be calculated in units of Solar mass directly from the orbital radius and orbital period of the planet or stars using Kepler's third law.