Solar apex

The solar apex, or the Apex of the Sun's Way, refers to the direction that the Sun travels through space. This is not to be confused with the Sun's apparent motion through the constellations of the zodiac, which is illusory -- this supposed motion is actually caused by the Earth revolving around the Sun.

Astronomy

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) RA|18|28|0 and declination (dec) of 30° North (in galactic coordinates: 56.24° longitude, 22.54° latitude). The radioastronomical position is RA RA|18|03|50.2 and dec DEC|30|00|16.8 (galactic coordinates: 58.87° longitude, 17.72° latitude).

The stars in the Galaxy's disk orbit around the Galactic Center. It would take the solar system about 226 million years to complete one orbit ("galactic year"), and so is thought to have completed about 25 orbits during its lifetime. The orbital speed is 217 km/s (485,400 miles per hour), i.e. 1 lightyear in about 1,400 years, and 1 AU in 8 days. The sun's motion in the Milky Way is also more complex than might be immediately supposed [ [http://www.americanscientist.org/template/AssetDetail/assetid/21173/page/2?&print=yes American Scientist Online ] ]

The orbital speed of stars in the Milky Way does not depend much on the distance to the center: it is always between 200 and 250 km/s for the Sun's neighbours [ [http://zebu.uoregon.edu/~imamura/123/lecture-2/mass.html Mass of the Milky Way ] ] . Hence the orbital period is approximately proportional to the distance from the star to the Galaxy's center (without the power 1.5 which applies in the case of a central mass). The disk has a bulge at the center.

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

References