# Star Motion, an interesting star concept. Reply

To budding astronomers.

A difference between true velocity and proper velocity. Proper velocity (proper motion) is the motion of a star apparent to the center-of-mass of the solar system. That is, how fast any object (a star) is moving wrt the sun’s position. (in terms of its center-of-mass)

So if a star is close to sun, its true velocity might be as much as it is, but proper velocity can be larger. Proper velocities are often larger when stars are closer, an useful fact in Astronomy.

(How proper velocity is eg useful in Astronomy, should be a good essay type question in Indian University exams, in the course of astronomy, but rather its more useful to remove essay type questions from Exams of University and such essay should be written by students as blogs, and the best blogs can be rewarded, Change should be brought to our education system by innovative thinking and not just by lecturing on outdated spiritual discourses)

eg Barnard’s star has the highest proper velocity among stars (it covers an angle of 10.3 arc-seconds per year) But its true velocity is 142 km/sec. (this, say, is 12 times faster than our rockets going to space)

But the highest true velocity of any star is by Wolf 424, which moves at 555 kms/sec. (wrt sun)

Barnard’s star is the 3rd closest star of earth. (technically, 5th closest, as there are 3 stars at the 2nd position) But Wolf 424 is quite far away hence it does not have a large proper velocity, but its actually moving quite fast, fastest among stars. In-fact its moving close to 50 times faster than our space-ships hence its closer to providing Relativistic effects. Its only 540 times slower compared to light’s speed, an unimaginably large speed.

Also note that true velocity is a velocity per se’. But proper velocity is an angular displacement rate. So its an angular velocity, an angle swept by the position of a star wrt center of mass of solar system.

While you are at stars here is something interesting about stars, they change their constellations due to proper motion etc.

There are politicians among stars. The ones that change their constellations, due to proper motion. Rho Aquilae became a politician in 1992. Gama Caeli will become a politician in 2400. Needless to say constellations are political parties of star.