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The Sun follows the solar circle (eccentricity e < 0.1) at a speed of about 255 km/s in a clockwise direction when viewed from the galactic north pole at a radius of ≈ 8.34 kpc [4] about the center of the galaxy near Sgr A*, and has only a slight motion, towards the solar apex, relative to the LSR. [5] [6]
The comoving distance from an observer to a distant object (e.g. galaxy) can be computed by the following formula (derived using the Friedmann–Lemaître–Robertson–Walker metric): = ′ (′) where a(t′) is the scale factor, t e is the time of emission of the photons detected by the observer, t is the present time, and c is the speed of ...
The Sun, taking along the whole Solar System, orbits the galaxy's center of mass at an average speed of 230 km/s (828,000 km/h) or 143 mi/s (514,000 mph), [167] taking about 220–250 million Earth years to complete a revolution (a Galactic year), [168] having done so about 20 times since the Sun's formation.
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 ...
This motion is caused by the movement of the stars relative to the Sun and Solar System. The Sun travels in a nearly circular orbit (the solar circle ) about the center of the galaxy at a speed of about 220 km/s at a radius of 8,000 parsecs (26,000 ly) from Sagittarius A* [ 5 ] [ 6 ] which can be taken as the rate of rotation of the Milky Way ...
The Sun is part of one of the Milky Way's outer spiral arms, known as the Orion–Cygnus Arm or Local Spur. [272] [273] It is a member of the thin disk population of stars orbiting close to the galactic plane. [274] Its speed around the center of the Milky Way is about 220 km/s, so that it completes one revolution every 240 million years. [271]
Speed is the magnitude of velocity (a vector), which indicates additionally the direction of motion. Speed has the dimensions of distance divided by time. The SI unit of speed is the metre per second (m/s), but the most common unit of speed in everyday usage is the kilometre per hour (km/h) or, in the US and the UK, miles per hour (mph).
In galactic astronomy, peculiar motion refers to the motion of an object (usually a star) relative to a Galactic rest frame. Local objects are commonly examined as to their vectors of position angle and radial velocity. These can be combined through vector addition to state the object's motion relative to the Sun.