Solar apex

The solar apex is in the constellation of Hercules near the star Vega.{{cite book | title=Three Hundred and Sixty Five Starry Nights: An Introduction to Astronomy for Every Night of the Year | first=Chet | last=Raymo | year=1990 | publisher=Touchstone | isbn=9780671766061 | url=https://books.google.com/books?id=rTe5HaRsAS4C&pg=PA114 }}

For more than 30 years before 1986 the speed of the Sun towards the solar apex was taken to be about 20 km/s{{cite journal|first1=Frank J. |last1=Kerr |author-link1=Frank John Kerr |first2=Donald |last2=Lynden-Bell |author-link2=Donald Lynden-Bell |title=Review of Galactic Constants |journal=Monthly Notices of the Royal Astronomical Society |date=August 1986 |volume=221 |issue=4 |pages=1023–1038 |doi=10.1093/mnras/221.4.1023 |bibcode=1986MNRAS.221.1023K |doi-access=free }} See also Table 3 on page 13 of {{Cite journal |last=Kogut |first=A. |date=1993 |title=Dipole Anisotropy in the COBE Differential Microwave Radiometers First-Year Sky Maps |journal=Astrophysical Journal |volume=419 |page=1 |arxiv=astro-ph/9312056 |doi=10.1086/173453|bibcode = 1993ApJ...419....1K |s2cid=209835274 |display-authors=etal}} but all later studies give a smaller component in the vector toward galactic longitude 90°, reducing overall speed to about 13.4 km/s.U, V, and W (vectors) are {{circa}} 10.0, 5.25 and 7.17 km/s respectively, {{cite journal|first1=Walter |last1=Dehnen |first2=James J. |last2=Binney |author-link2=James Binney |title=Local Stellar Kinematics from Hipparcos Data |journal=Monthly Notices of the Royal Astronomical Society |date=1998 |volume=298 |issue=2 |pages=387–394 |doi=10.1046/j.1365-8711.1998.01600.x |doi-access=free |arxiv=astro-ph/9710077 |bibcode=1998MNRAS.298..387D |s2cid=15936627 }} 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 {{frac|1|13}} 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.{{cite magazine |last=Frisch |first=Priscilla |year=2000 |archive-url=https://web.archive.org/web/20071124131720/http://www.americanscientist.org/template/AssetDetail/assetid/21173/page/2?&print=yes |url=http://www.americanscientist.org/template/AssetDetail/assetid/21173/page/2?&print=yes |archive-date=2007-11-24 |title=The Galactic Environment of the Sun |magazine=American Scientist |volume=88 |number=1 |page=52}}

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.{{cite book |first=John |last=Lankford |date=1997 |title=History of Astronomy: An Encyclopedia |page=[https://archive.org/details/historyofastrono00john/page/258 258] |volume=1 |series=Garland Encyclopedias in the History of Science |publisher=Taylor & Francis |isbn=0-8153-0322-X |url-access=registration |url=https://archive.org/details/historyofastrono00john/page/258 }}{{cite journal |jstor=106492 |last1=Herschel |first1=William |author-link=William Herschel |date=1783 |title=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] |journal=Philosophical Transactions of the Royal Society of London |volume=73 |pages=247–83 |doi=10.1098/rstl.1783.0017 |s2cid=186213288 }}

Herschel was not an observer–he relied on star motions reported in existing catalogs by Nevil Maskelyne and Jérôme Lalande- and he was not an especially skilled mathematician but his result was close to modern values.{{citation

| title=Herschel's Determination of the Solar Apex

| last1=Hoskin | first1=Michael

| journal=Journal for the History of Astronomy

| volume=11 | pages=153–163 | year=1980

| issue=3 | bibcode=1980JHA....11..153H | postscript=. | doi=10.1177/002182868001100301| s2cid=115478560 }}

Many calculations of the solar apex have been published as new catalogues of stars were published.{{Cite journal |last=Walkey |first=O. R. |date=1946-08-01 |title=An Abstract on the Solar Apex |journal=Monthly Notices of the Royal Astronomical Society |volume=106 |issue=4 |pages=274–279 |doi=10.1093/mnras/106.4.274 |doi-access=free |issn=0035-8711}} The catalog from the Hipparcos astrometric satellite and measurements with objective prisms lead to a new set of values.{{Cite journal |last1=Fehrenbach |first1=Ch. |last2=Duflot |first2=M. |last3=Burnage |first3=R. |date=April 2001 |title=New determination of the solar apex |url=http://www.aanda.org/10.1051/0004-6361:20010100 |journal=Astronomy & Astrophysics |volume=369 |issue=1 |pages=65–73 |doi=10.1051/0004-6361:20010100 |bibcode=2001A&A...369...65F |issn=0004-6361}} These two results do not agree. The calculation of the local standard of rest itself is subject to issues due to inhomogeneous stellar velocities{{Cite journal |last1=Francis |first1=Charles |last2=Anderson |first2=Erik |date=2009-10-01 |title=Calculation of the local standard of rest from 20 574 local stars in the New Hipparcos Reduction with known radial velocities |url=https://www.sciencedirect.com/science/article/pii/S1384107609000384 |journal=New Astronomy |volume=14 |issue=7 |pages=615–629 |doi=10.1016/j.newast.2009.03.004 |issn=1384-1076|arxiv=0812.4032 |bibcode=2009NewA...14..615F }}

and high sensitivity to parameters.{{Cite journal |last1=Bobylev |first1=V. V. |last2=Bajkova |first2=A. T. |date=2014-04-21 |title=The local standard of rest from data on young objects with account for the Galactic spiral density wave |journal=Monthly Notices of the Royal Astronomical Society |volume=441 |issue=1 |pages=142–149 |doi=10.1093/mnras/stu563 |doi-access=free |issn=1365-2966|arxiv=1404.6987 }}

The solar antapex, the direction opposite of the solar apex, is located near the star Zeta Canis Majoris.{{Cite web |title=Furud |url=http://stars.astro.illinois.edu/sow/furud.html |access-date=2024-05-26 |website=stars.astro.illinois.edu}}

Image:Astro_4D_milkyway_stars_proper_radial_all_all_anim.gif|The movement of stars around the apex (left) and antapex (right) in ± 500 000 years. To view this picture you need 3D glasses (red-green or red-blue).

Image:Astro_4D_milkyway_stars_proper_radial_all_apex_anim.gif|The movement of stars around the apex. To view this picture you need 3D glasses (red-green or red-blue).

Image:Astro_4D_milkyway_stars_proper_radial_all_antapex_anim.gif|The movement of stars around the antapex. To view this picture you need 3D glasses (red-green or red-blue).

Image:Astro_4D_milkyway_stars_proper_radial_all_mid_anim.gif|The movement of stars between apex and antapex. To view this picture you need 3D glasses (red-green or red-blue).

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

{{Reflist}}

{{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}}

Category:Dynamics of the Solar System

Category:Hercules (constellation)