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Self motion refers to the angle (lateral motion) of the distance traveled by a star to the observer within a year.The space motion of a star to the sun can be divided into two components: the radial motion and the lateral motion. The latter is often measured by the displacement of a star with weak background on the celestial sphere, and the unit is angular seconds per year.The self motion is usually very small. Only 200 stars reach 1 jiao second per year, 50 of which reach 2 jiao seconds per year“Barnard star”Its self motion is the largest, reaching 10.31 angular seconds every year, which is 0.5% of the angular diameter of the moon seen on the earth.[1]
The phenomenon of self motion was discovered by Edmund Halley in 1718 AD. When comparing his astrometric data of Sirius, Arcturus and Aldebaran with the position data described by the ancient Greek astronomer Hibakus before 1850, Halley noticed that some data were more than half a degree different, so he deduced this phenomenon.
In the research report published in 2005, modern astronomers have measured the first alien system（Triangle galaxy）'s own motion data.
The angle of the star to the observer at the distance perpendicular to the line of sight in a year.Its unit isAngular second/Years.In 1718, E. Haley compared the positions of stars he observed at that time with the observations of Hipparchus and Ptolemy, and found that the positions of stars had significant changes. He pointed out for the first time that the concept of star immobility was wrong.
In fact, stars move in space.ObservedStellar motionIncluding: ① the real motion of stars, also known as the intrinsic motion. ②Apparent motion caused by solar motion, also known asApparent differential。The self motion of stars is very small, generally less than 0 ″. 1 per year.Only more than 400 stars have a self motion equal to or greater than 1 ″ per year, and Barnard has the largest self motion, which is 10 ″ per year. 31.In addition to the self motion, there is also precession, which together is called the annual change of stars.When the influence of precession is eliminated, the absolute self motion can be obtained
Day after day, the stars seem to have fixed relative positions with each other, forming the same constellation pattern in the skyBig DipperIt seems that nothing has changed for thousands of years.But long-term observation shows that the constellation will slowly change its shape, and each star in the sky has its own way of movement, but the change is very slow and cannot be detected without precise measurement.
This change in the position of stars in the sky is caused by the relative motion of stars and the solar system.We usually use two quantities to describe it: self motion angle and self motion speed.The first number indicates the direction of self movement on the celestial sphere (the east is on the left, and clockwise starts from the north), and the second number indicates the size of the movement speed, expressed in angular seconds per year.
Barnard starIt is the largest self moving star among all known stars, moving at a speed of 10.3 angular seconds every year.The greater the self motion, the closer a star is to the solar system.This is indeed the case of Barnard star, which is only about 6 light years away from us. It is the second closest star to the solar system except for the South Gate II system (Alpha Centauri Trinity).However, because it is a red dwarf star, its brightness is only 9.54 magnitude, and its brightness is weak. It cannot be observed without large aperture telescopes or high-powered binoculars.
One angular second per year is equivalent to a lateral speed of 1.45 kilometers per second at a distance of one light year.Therefore, we can know that the lateral velocity of Barnard is about 90 kilometers per second;Add the visual speed of 111 kilometers per second to get the real speed of 143 kilometers per second.In general, it is difficult to measure the true or absolute motion rate of stars, because it strongly depends on the accuracy of the distance measurement of stars.The neighboring star known to have the maximum speed of motion (relative to the solar system) is Wolf 424, which moves at the rate of 555 kilometers per second.Among the known stars, only the neighboring stars that slightly cross half can infer their absolute moving speed.
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Self motion in astronomy refers to the change of a star's position in the sky after eliminating non self motion, that is, the motion perpendicular to the line of sight.Non self motion is not the real motion of the celestial body itself, but caused by some factors that will affect the coordinate value of the observed celestial body's position. These factors mainly include:
The following table shows some stars with the largest self motion known in the Hipparcos catalog, [1] but does not include stars like en: Teegarden's star that are in the catalog but have too dim luminosity.
High self motion star [2] # star self motion radial
