PDF Slides - UMBC

… this can be quite a biggie too for some stars …
4) Proper Motion of Objects [text Sect.2.2]
No object in the Universe is “stationary”
(& “stationary” can’t be defined on its own anyhow of course)
… thus even after correcting for the spin & orbit of the Earth
all objects are moving with respect to our chosen
coordinate system
(unless it was the basis of our coordinate system of course)
Proper Motion is the term used to describe the
“velocity” of objects “on the plane of the sky”
it is almost always quoted in arcsec/yr (few “/yr for nearest starts)
obviously given the direction of motion
is trivial to correct (α,δ) (J2000) for observation date
Ian M. George PHYS 304 (2011 Fall) Meeting 04