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.