  Spectroscopic, photometric and dynamical data of the inner 3 kpc part of the
starburst galaxy M82 are analyzed in order to investigate the star formation
history of the stellar disk. The long-slit spectra along the major axis are
dominated by Balmer absorption lines in the region outside the nuclear
starburst all the way up to ~3.5 scalelengths (mu_B=22 mag/arcsec**2). Single
Stellar Population (SSP) spectra of age 0.4-1.0 Gyr match well the observed
spectra in the 1-3 kpc zone, with a mean age of the stellar population
marginally higher in the outer parts. The mass in these populations, along with
that in the gas component, make up for the inferred dynamical mass in the same
annular zone for a Kroupa initial mass function, with a low mass cut-off
m_l=0.4 Msun. The observed ratio of the abundances of alpha elements with
respect to Fe, is also consistent with the idea that almost all the stars in
M82 disk formed in a burst of short duration (0.3 Gyr) around 0.8 Gyr ago. We
find that the optical/near infrared colors and their gradients in the disk are
determined by the reddening with visual extinction exceeding 1 mag even in the
outer parts of the disk, where there is apparently no current star formation.
The disk-wide starburst activity was most likely triggered by the interaction
of M82 with its massive neighbor M81 around 1~Gyr ago. The properties of the
disk of M82 very much resemble the properties of the disks of luminous compact
blue galaxies seen at 0.2-1.0 redshift.
