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The galactic year, also known as a cosmic year, is the duration of time required for the Sun to orbit once around the center of the Milky Way Galaxy. [1] One galactic year is approximately 225 million Earth years. [2]
At the equator, the solar rotation period is 24.47 days. This is called the sidereal rotation period, and should not be confused with the synodic rotation period of 26.24 days, which is the time for a fixed feature on the Sun to rotate to the same apparent position as viewed from Earth (the Earth's orbital rotation is in the same direction as the Sun's rotation).
Figure 1: Geometry of the Oort constants derivation, with a field star close to the Sun in the midplane of the Galaxy. Consider a star in the midplane of the Galactic disk with Galactic longitude at a distance from the Sun. Assume that both the star and the Sun have circular orbits around the center of the Galaxy at radii of and from the Galactic Center and rotational velocities of and ...
The apex of the Sun's way, or the solar apex, is the direction that the Sun travels through space in the Milky Way. The general direction of the Sun's Galactic motion is towards the star Vega near the constellation of Hercules, at an angle of roughly 60 sky degrees to the direction of the Galactic Center. The Sun's orbit about the Milky Way is ...
The Sun is moved by the gravitational pull of the planets. The center of the Sun moves around the Solar System barycenter, within a range from 0.1 to 2.2 solar radii. The Sun's motion around the barycenter approximately repeats every 179 years, rotated by about 30° due primarily to the synodic period of Jupiter and Saturn. [152]
The inclination of the moon's orbit is shown relative to the Ecliptic Plane. The Solar System traces out a sinusoidal path in its orbit around the galactic center. Using Galactic North as the initial frame of reference, the Earth and Sun rotate counterclockwise, and the Earth revolves in a counterclockwise direction around the Sun.
[4] [33] For comparison, the radius of Earth's orbit around the Sun is about 150 million kilometers (1.0 AU), whereas the distance of Mercury from the Sun at closest approach is 46 million kilometers (0.3 AU). Thus, the diameter of the radio source is slightly less than the distance from Mercury to the Sun.
Thus, the Sun occupies 0.00001% (1 part in 10 7) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1 millionth (10 −6) that of the Sun. Jupiter, the largest planet, is 5.2 AU from the Sun and has a radius of 71,000 km (0.00047 AU; 44,000 mi), whereas the most distant planet, Neptune, is 30 AU ...