|Gravitational effects of
planet means star orbits center of mass of system. Over 30 yrs, Sun moves
thus, mostly (70%) due to Jupiter. Mjup ~ 1/1000Msun, so c.of m. 1000x closer
to Sun than Jup. Total wobble 4mas =separation of headlights of car at 20,000km.
Easiest to detect velocity variations, especially for planets close to star
which move fast 12m/sec due to Jup. Astrometry a difficult measure