  Astrometry from Gaia will measure the positions of stellar photometric
centroids to unprecedented precision. We show that the precision of Gaia
astrometry is sufficient to detect starspot-induced centroid jitter for nearby
stars in the Tycho-Gaia Astrometric Solution (TGAS) sample with magnetic
activity similar to the young G-star KIC 7174505 or the active M4 dwarf GJ
1243, but is insufficient to measure centroid jitter for stars with Sun-like
spot distributions. We simulate Gaia observations of stars with 10 year
activity cycles to search for evidence of activity cycles, and find that Gaia
astrometry alone likely can not detect activity cycles for stars in the TGAS
sample, even if they have spot distributions like KIC 7174505. We review the
activity of the nearby low-mass stars in the TGAS sample for which we
anticipate significant detections of spot-induced jitter.
