The Star Formation History of the Milky Way
Quantification of the Galaxy's star formation history involves both the duration and the rate of formation, with these parameters being known with different precision for different populations. The early rate of star formation is knowable from modelling chemical element data, the recent rate directly from isochrone analyses of colour-magnitude data. The field halo and globular clusters are almost exclusively old, and formed in at most a few Gyr. The outer bulge probably formed in a short period long ago -- extant data is inconsistent, while the inner bulge/disk is forming today, and has continued to form over time. Only very limited data is available on the inner disk. The outer disk near the Sun seems as old as the halo. The earliest extended disk, which forms the thick disk today, seems to have been in place very early, an observation which is not simply consistent with some galaxy formation models.