Milky Way
(Muhammad Unza Farooqui, Karachi)
The Milky Way is a barred
spiral galaxy, about 100,000 light-years across. If you could look down on it
from the top, you would see a central bulge surrounded by four large spiral arms
that wrap around it. Spiral galaxies make up about two-third of the galaxies in
the universe.
The Milky Way does not sit still, but is constantly rotating. As such, the arms
are moving through space. The sun and the solar system travel with them. The
solar system travels at an average speed of 515,000 miles per hour (828,000
kilometers per hour). Even at this rapid speed, the solar system would take
about 230 million years to travel all the way around the Milky Way.