World Library  
Flag as Inappropriate
Email this Article

Solar mass

Article Id: WHEBN0000172987
Reproduction Date:

Title: Solar mass  
Author: World Heritage Encyclopedia
Language: English
Subject: Val/list, Infobox star, Infobox star/doc, Stellar classification, Val/unitswithlink/testcases
Collection: Sun, Units of Mass, Units of Measurement in Astronomy
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Solar mass

Size and mass of very large stars: Most massive example, the blue Pistol Star (150 M). Others are Rho Cassiopeiae (40 M), Betelgeuse (20 M), and VY Canis Majoris (17 M). The Sun (1 M) which is not visible in this thumbnail is included to illustrate the scale of example stars. Earth's orbit (grey), Jupiter's orbit (red), and Neptune's orbit (blue) are also given.

The solar mass (M) is a standard unit of mass in astronomy that is used to indicate the masses of other stars, as well as clusters, nebulae and galaxies. It is equal to the mass of the Sun, about two nonillion kilograms:

M = (1.98855±0.00025)×1030 kg[1][2]

The above mass is about 332946 times the mass of the Earth (M), or 1048 times the mass of Jupiter (MJ).

Because the Earth follows an elliptical orbit around the Sun, its solar mass can be computed from the equation for the orbital period of a small body orbiting a central mass.[3] Based upon the length of the year, the distance from the Earth to the Sun (an astronomical unit or AU), and the gravitational constant (G), the mass of the Sun is given by:

M_\odot = \frac{4 \pi^2 \times (1\,\mathrm{AU})^3}{G \times (1\,\mathrm{yr})^2}

The value of the gravitational constant was first derived from measurements that were made by Henry Cavendish in 1798 with a torsion balance. The value he obtained differs by only 1% from the modern value.[4] The diurnal parallax of the Sun was accurately measured during the transits of Venus in 1761 and 1769,[5] yielding a value of 9″ (9 arcseconds, compared to the present 1976 value of 8.794148). If we know the value of the diurnal parallax, we can determine the distance to the Sun from the geometry of the Earth.[6]

The first person to estimate the mass of the Sun was Isaac Newton. In his work Principia, he estimated that the ratio of the mass of the Earth to the Sun was about 1/28 700. 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 (1 AU). He corrected his estimated ratio to 1/169 282 in the third edition of the Principia. The current value for the solar parallax is smaller still, yielding an estimated mass ratio of 1/332 946.[7]

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 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, provided that orbital radius is measured in astronomical units and orbital period is measured in years.

The mass of the Sun has decreased since the time it formed. This has occurred through two processes in nearly equal amounts. First, in the Sun's core hydrogen is converted into helium by nuclear fusion, in particular the pp chain, and this reaction converts some mass into energy in the form of gamma ray photons. Most of this energy eventually radiates away from the Sun. Second, high-energy protons and electrons in the atmosphere of the Sun are ejected directly into outer space as a solar wind.

The original mass of the Sun at the time it reached the main sequence remains uncertain. The early Sun had much higher mass-loss rates than at present, so it may have lost anywhere from 1–7% of its natal mass over the course of its main-sequence lifetime.[8] The Sun gains a very small mass through the impact of asteroids and comets; however the Sun already holds 99.86% of the Solar System's total mass, so these impacts cannot offset the mass lost by radiation and ejection.

Contents

  • Related units 1
  • See also 2
  • References 3
  • Further reading 4

Related units

One solar mass, M, can be converted to related units:

It is also frequently useful in general relativity to express mass in units of length or time.

See also

References

  1. ^ 2014 Astronomical Constants http://asa.usno.navy.mil/static/files/2014/Astronomical_Constants_2014.pdf
  2. ^ NIST CODATA http://physics.nist.gov/cgi-bin/cuu/Value?bg
  3. ^ Harwit, Martin (1998), Astrophysical concepts, Astronomy and astrophysics library (3rd ed.), Springer, pp. 72, 75,  
  4. ^ Holton, Gerald James; Brush, Stephen G. (2001). Physics, the human adventure: from Copernicus to Einstein and beyond (3rd ed.). Rutgers University Press. p. 137.  
  5. ^ Pecker, Jean Claude; Kaufman, Susan (2001). Understanding the heavens: thirty centuries of astronomical ideas from ancient thinking to modern cosmology. Springer. pp. 291–291.  
  6. ^ Barbieri, Cesare (2007). Fundamentals of astronomy. CRC Press. pp. 132–140.  
  7. ^ Leverington, David (2003). Babylon to Voyager and beyond: a history of planetary astronomy. Cambridge University Press. p. 126.  
  8. ^ Sackmann, I.-Juliana; Boothroyd, Arnold I. (February 2003), "Our Sun. V. A Bright Young Sun Consistent with Helioseismology and Warm Temperatures on Ancient Earth and Mars", The Astrophysical Journal 583 (2): 1024–1039,  

Further reading

  • I.-J. Sackmann; A. I. Boothroyd (2003). "Our Sun. V. A Bright Young Sun Consistent with Helioseismology and Warm Temperatures on Ancient Earth and Mars". The Astrophysical Journal 583 (2): 1024–1039.  
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.