Download Milky Way structure

• What is the closest galaxy to the Milky Way? The new
answer to this old question is the Canis Major dwarf
galaxy. For many years astronomers thought the
Large Magellan Cloud (LMC) was closest, but its title
was supplanted in 1994 by the Sagittarius dwarf
galaxy. Recent measurements indicate that the Canis
Major dwarf is only 42,000 light years from the
Galactic center, about three quarters of the distance to
the Sagittarius dwarf and a quarter of the distance to
the LMC. The discovery was made in data from the
2MASS-sky survey, where infrared light allows a better
view through our optically opaque Galactic plane. The
labeled illustration above shows the location of the
newly discovered Canis Major dwarf and its
associated tidal stream of material in relation to our
Milky Way Galaxy. The Canis Major dwarf and other
satellite galaxies are slowly being gravitationally
ripped apart as they travel around and through our
Galaxy.
• RR Lyrae is the prototype of a class of
variables (that is, the ‘main’ star in that
category, usually the first star discovered
with its particular characteristics).
RR Lyrae variables are very old giants
which pulsate (that is their outer layer
expands and contracts). Their period is
quite short, less than one day. They
usually inhabit globular clusters.
• RR Lyrae has a period of 13h 36m and a
range of one full magnitude, 7.1 to 8.1.