The solar apex, or the apex of the Sun's way, refers to the direction that the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

travels with respect to the

local standard of rest In astronomy, the local standard of rest or LSR follows the mean motion of material in the Milky Way in the neighborhood of the Sun (stars in radius 100 pc from the Sun). The path of this material is not precisely circular. The Sun follows the sola ...

. This is not to be confused with the Sun's apparent motion through all

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

s of the

zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the Sun path, apparent path of the Sun across the celestial sphere over the course of the year. ...

, which is an illusion caused by the orbit of the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

Direction

The solar apex is in the constellation of

Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...

, southwest of

Vega Vega is the brightest star in the northern constellation of Lyra. It has the Bayer designation α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, an ...

, northeast of his "outstretched arm",

Omicron Herculis Omicron Herculis, Latinized from o Herculis, is a star in the constellation Hercules. It used to be called Masym ("the wrist"), but this name was transferred to Lambda Herculis. Properties Omicron Herculis is a B9.5III star approxim ...

. There are two mainstream sets of coordinates for the solar apex. *The visual coordinates (as obtained by visual observation of the apparent motion) are

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the earth. When paired w ...

(RA) ,

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...

(dec) 30° N **in

galactic coordinates The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane parallel to an a ...

: 56.24° longitude, +22.54° latitude **in

ecliptic coordinates The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System bodi ...

: 271.79° longitude, +53.43° latitude. *The radioastronomical position is RA , dec + (galactic coordinates: 58.87° longitude, 17.72° latitude). Evaluation of movement of the Solar System in its neighborhood is complex; a selection of links is on the

Talk page MediaWiki is a Free and open-source software, free and open-source wiki software. It is used on Wikipedia and almost all other Wikimedia movement, Wikimedia Website, websites, including Wiktionary, Wikimedia Commons and Wikidata; these sit ...

of this article. For more than 30 years before 1986 the speed of the Sun towards the solar apex was taken to be about 20 km/s but all later studies give a smaller component in the vector toward

galactic longitude The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane parallel to an a ...

90°, reducing overall speed to about 13.4 km/s. This speed is not to be confused with the

orbital speed In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter or, if one body is much more massi ...

of the Sun around the

Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact rad ...

, which is about 220 km/s and is included in the movement of the

Local standard of rest In astronomy, the local standard of rest or LSR follows the mean motion of material in the Milky Way in the neighborhood of the Sun (stars in radius 100 pc from the Sun). The path of this material is not precisely circular. The Sun follows the sola ...

. 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.Frisch, Priscilla (2000)
"The Galactic Environment of the Sun"
''American Scientist'', volume 88, number 1, page 52

History

The nature and extent of the solar motion was first demonstrated by

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...

in 1783, who also first determined the direction for the solar apex, as

Lambda Herculis Lambda Herculis (λ Herculis. abbreviated Lambda Her, λ Her), formally named Maasym , is a star in the constellation of Hercules. From parallax measurements taken during the Gaia mission, it is approximately 393 light-years from the S ...

, 10° away from today's accepted position.

Solar antapex

The solar antapex, the direction opposite of the solar apex, is located near the star

Zeta Canis Majoris Zeta Canis Majoris, or ζ Canis Majoris, also named Furud , is a binary star system in the southern constellation of Canis Major. This system has an apparent visual magnitude of +3.0, making it one of the brighter stars in the conste ...

Gallery

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 Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is ...

(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).

References

{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System Dynamics of the Solar System

Direction

History

Solar antapex

Gallery

See also

References