The Milky Way
(latin: Via Lactea) is the dim stripe of nebulous light
which can be seen on a clear night in the direction of Sagittarius.
It's a fabulous side view of the disk-shaped system that includes
our Sun and billions of other stars like it.
In modern times,
a huge number of such systems were discovered.
The Milky Way is significantly larger than early estimates had indicated.
In December 2012, it was deduced
from years of observations by the Hubble Soace Telescope
that the neighbohring dwarf galaxy known as
Leo 1 is in orbit around the center of the Milky way at a speed
comparable to our Sun's own orbital speed.
To create the corresponding gravitational pull, the total mass of the
Milky Way ought to be 1.6 trillion
solar masses or so (counting everything,
dark matter spherical halo and all, at a
lesser distant from the galactic center than Leo 1 itself).
The definitive guide to
the milky way galaxy NASA, JPL, National Geographic Chanel.
Space Fan News #84
by Tony Darnell (2012-12-04).
Galaxy rotation curve