Solar apex

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The movement of stars of spectral classes B and A around the apex (left) and antapex (right) in ± 200 000 years.

The solar apex (Apex of the Sun's Way) is the direction that the Sun travels with respect to the Local Standard of Rest. In layman terms, it's the "target" within the Milky Way that the Sun appears to be "chasing" as it orbits the galaxy. It should not be confused with the Sun's "motion" through the Zodiac, which is not a real 3D motion, but a 2D parallax effect due to change in the vantage point of an observer on Earth (the Earth's revolving around the Sun).

The general direction of the solar apex is southwest of the star Vega near the constellation of Hercules. There are several coordinates for the solar apex. The visual coordinates (as obtained by visual observation of the apparent motion) is right ascension (RA) 18h 28m 0s and declination (dec) of 30° North (in galactic coordinates: 56.24° longitude, 22.54° latitude). The radioastronomical position is RA 18h 03m 50.2s and dec 30° 00′ 16.8″ (galactic coordinates: 58.87° longitude, 17.72° latitude).

The Sun moves towards the apex at about 16.5 km/s. This is relative to the Sun's general orbital speed around the Galactic center, about 220 km/s, already included in the Local Standard of Rest. Thus the Sun gains distance towards the apex at about 1/13 its orbital speed. The sun's motion in the Milky Way is more complex than a simple orbit, it also shifts ("bobs") up and down with respect to the galactic plane.[1]

The nature and extent of the solar motion was first demonstrated by William Herschel in 1783.

The solar antapex, the direction opposite of the solar apex, is located near the star Zeta Canis Minoris.



  1. ^ Priscilla Frisch (2000). "The Galactic Environment of the Sun", American Scientist.