The
Milky Way – Then & Now
The
View from GalileoÕs Telescope
Galileo first studied the
Milky Way through his telescope in January, 1610. Until his observations, the
Milky Way was thought to be a band of wispy whitish clouds passing through the
heavens. To GalileoÕs amazement, instead of seeing just a nebula (the Greek
work for cloud) the milky wisps resolved into innumerable tiny stars, so
crowded together that, without the aid of a telescope, the light from those
stars simply blended together.
Above: GalileoÕs sketch of a sky filled with
stars. (Image credit: Octavo Corp./Warnock Library)
Before the invention of the
telescope, the number of stars in the night sky, perhaps in the entire universe,
was just a few thousand (you can see at most 3000 stars in the night sky with
the unaided eye). If the Milky Way was indeed a dense swarm of stars as Galileo
now saw, then the number of stars in the universe could be measured in
millions!
What
did YOU See with MicroObservatory?
Have you seen the Milky
way? It is much clearer in the
summer months, it is best to be in quite a dark location (not easy to find in a
city!) Your MicroObservatory image
of the Milky Way covers the same area of sky that is blocked by your fist at
armÕs length. This is a larger
portion of the sky than GalileoÕs sketch depicts. How is your image similar to,
or different from, GalileoÕs description? How does it compare to your own
experience of the night sky?
Above: Archive MicroObservatory image of the Milky Way
To see the Milky Way in more
detail, you may want to open your image in our MicroObservatory
image processing software.
The
Milky Way - 400 years later
The Greek word for milk is gala, the origin of the word galaxy, and thatÕs exactly
what the Milky Way is. A galaxy is
a city of stars, and our Sun is just one of 200 billion stars in the Milky Way
galaxy. The cloudy band we see in
the night sky is an immense spiral galaxy, viewed from the inside.
Above: Our Milky way galaxy seen in infrared
light. There are over 500 million
stars visible in this image! (Image credit: 2MASS)
The Milky Way is indeed a
swarm of almost countless stars, just as Galileo discovered. However, there is
also a cloudy component too, as the Milky Way galaxy is filled with giant
clouds of gas and dust that form the raw material to make the next generation
of stars.
As we peer towards the
richest region of the Milky Way, in the constellation Sagittarius, we look
towards the center of the galaxy.
Through the ocean of countless stars and sweeping clouds of gas and
dust, we come to the very heart of the Milky Way. Using observations of the largest telescopes, such as the
Keck Telescope in Hawaii, and NASAÕs Chandra X-ray telescope, astronomers have
discovered a giant black hole that weighs as much as 4 million Suns. Astronomers have only just begun to
unravel the mysteries of the black hole and its role in the history of our
galaxy.
Above: An image of the center of our galaxy
by the Chandra X-ray telescope. (Image credit: NASA/CXC)
Find
Out More
2009 is International Year
of Astronomy, chosen to commemorate the 400th anniversary of
GalileoÕs discoveries with the telescope.
Find out what else is happening by visiting these web sites:
The World site for International Year of
Astronomy.
The United States national site for
International Year of Astronomy.
NASAÕs International Year of Astronomy
website.
For more information on the
2MASS survey, go to:
http://www.ipac.caltech.edu/2mass/
For more information on
Chandra observations of the Milky Way, go to
http://chandra.harvard.edu/press/category/milkyway.html
Take
a look at the full list of objects in MicroObservatoryÕs Galileo activity,
and see how our understanding has evolved over the last four centuries.