  I compare the structures of the bipolar nebulae around the massive binary
system Eta Carinae and around the low mass binary system HD 44179. While Eta
Carinae is on its way to become a supernova, the Red Rectangle is on its way to
form a planetary nebula. Despite the two orders of magnitude difference in
mass, these two systems show several similarities, both in the properties of
the stellar binary systems and the nebulae. From this comparison and further
analysis of the accretion process during the 20 years Great Eruption of Eta
Carinae, I strengthen the binary model for the formation of its bipolar
nebula--the Homunculus. In the binary model a large fraction of the mass lost
by the primary star during the Great Eruption was transferred to the secondary
star (the companion); An accretion disk was formed around the companion, and
the companion launched two opposite jets. I show that the gravitational energy
of the mass accreted onto the secondary star during the Great Eruption can
account for the extra energy of the Great Eruption, both the radiated energy
and the kinetic energy in the Homunculus. I also conclude that neither the
proximity of the primary star in Eta Car to the Eddington luminosity, nor the
rotation of the primary star are related directly to the shaping of the
Homunculus. I speculate that the Great Eruption of Eta Carinae was triggered by
disturbance in the outer boundary of the convective region, most likely by
magnetic activity, that expelled the outer radiative zone.
