Solar apex explained

The solar apex, or the apex of the Sun's way, refers to the direction that the Sun travels with respect to the local standard of rest. This is not to be confused with the Sun's apparent motion through all constellations of the zodiac, which is an illusion caused by the orbit of the Earth.

Direction

The solar apex is in the constellation of Hercules near the star Vega^[1]

For more than 30 years before 1986 the speed of the Sun towards the solar apex was taken to be about 20 km/s^[2] but all later studies give a smaller component in the vector toward galactic longitude 90°, reducing overall speed to about 13.4 km/s.^[3] This speed is not to be confused with the orbital speed of the Sun around the Galactic Center, which is about 220 km/s and is included in the movement of the Local standard of rest. Thus the Sun moves towards the apex (a relatively local point) at about our spiral arm's orbital speed. The Sun's motion in the Milky Way is not confined to the galactic plane; it also shifts ("bobs") up and down with respect to the plane over millions of years.^[4]

History

The nature and extent of the solar motion was first demonstrated by William Herschel in 1783, who also first determined the direction for the solar apex, as Lambda Herculis, 10° away from today's accepted position.^{[5] [6]}

Many calculations of the solar apex have been published as new catalogues of stars were published.^[7] The catalog from the Hipparcos astrometric satellite and measurements with objective prisms lead to a new set of values.^[8] These two results do not agree. The calculation of the local standard of rest itself is subject issues due to inhomogeneous stellar velocities^[9] and high sensitivity to parameters.^[10]

Solar antapex

The solar antapex, the direction opposite of the solar apex, is located near the star Zeta Canis Majoris.^[11]

See also

• Manuel Foster Observatory – southern observatory established for the determination of the Solar Apex by W. W. Campbell

Notes and References

1. Book: Raymo, Chet . Three Hundred and Sixty Five Starry Nights: An Introduction to Astronomy for Every Night of the Year . 1990 . Touchstone . 9780671766061 .
2. Frank J. . Kerr . Frank John Kerr . Donald . Lynden-Bell . Donald Lynden-Bell . Review of Galactic Constants . . August 1986 . 221 . 4 . 1023–1038 . 10.1093/mnras/221.4.1023 . 1986MNRAS.221.1023K . free . See also Table 3 on page 13 of Kogut . A. . 1993 . Dipole Anisotropy in the COBE Differential Microwave Radiometers First-Year Sky Maps . . 419 . 1 . astro-ph/9312056 . 10.1086/173453. 1993ApJ...419....1K . 209835274 . etal.
3. U, V, and W (vectors) are 10.0, 5.25 and 7.17 km/s respectively, Walter . Dehnen . James J. . Binney . James Binney . Local Stellar Kinematics from Hipparcos Data . . 1998 . 298 . 2 . 387–394 . 10.1046/j.1365-8711.1998.01600.x . free . astro-ph/9710077 . 1998MNRAS.298..387D . 15936627 .
4. Frisch . Priscilla . 2000 . https://web.archive.org/web/20071124131720/http://www.americanscientist.org/template/AssetDetail/assetid/21173/page/2?&print=yes . The Galactic Environment of the Sun . 2007-11-24 . . 88 . 1 . 52.
5. Book: Lankford, John . 1997 . History of Astronomy: An Encyclopedia . 258 . 1 . Garland Encyclopedias in the History of Science . . 0-8153-0322-X . registration .
6. 106492 . Herschel . William . William Herschel . 1783 . On the Proper Motion of the Sun and Solar System; With an Account of Several Changes That Have Happened among the Fixed Stars since the Time of Mr. Flamstead [sic] . Philosophical Transactions of the Royal Society of London . 73 . 247–83 . 10.1098/rstl.1783.0017 . 186213288 .
7. Walkey . O. R. . 1946-08-01 . An Abstract on the Solar Apex . Monthly Notices of the Royal Astronomical Society . 106 . 4 . 274–279 . 10.1093/mnras/106.4.274 . free . 0035-8711.
8. Fehrenbach . Ch. . Duflot . M. . Burnage . R. . April 2001 . New determination of the solar apex . Astronomy & Astrophysics . 369 . 1 . 65–73 . 10.1051/0004-6361:20010100 . 2001A&A...369...65F . 0004-6361.
9. Francis . Charles . Anderson . Erik . 2009-10-01 . Calculation of the local standard of rest from 20 574 local stars in the New Hipparcos Reduction with known radial velocities . New Astronomy . 14 . 7 . 615–629 . 10.1016/j.newast.2009.03.004 . 1384-1076. 0812.4032 . 2009NewA...14..615F .
10. Bobylev . V. V. . Bajkova . A. T. . 2014-04-21 . The local standard of rest from data on young objects with account for the Galactic spiral density wave . Monthly Notices of the Royal Astronomical Society . 441 . 1 . 142–149 . 10.1093/mnras/stu563 . free . 1365-2966. 1404.6987 .
11. Web site: Furud . 2024-05-26 . stars.astro.illinois.edu.