Solar apex

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 lay 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 our vantage point (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) 18^h 28^m 0^s and declination (dec) of 30° North (in galactic coordinates: 56.24° longitude, 22.54° latitude). The radioastronomical position is RA 18^h 03^m 50.2^s and dec 30° 00′ 16.8″ (galactic coordinates: 58.87° longitude, 17.72° latitude).

The speed of the Sun towards the solar apex is about 16.5 km/s. 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. 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.

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.

Gallery

• Animations of star motions around apex and atapex
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  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).

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

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

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