calendars. Telescopes were invented in the
17th century. Astronomers then mapped
the sky in greater detailPPstill with visible
light. They learned about the temperature,
constituents, distribution, and the motions of
stars. In the 20th century, scientists began to explore the other regions of the spectrum. Each region provided new evidence about the universe. Radio waves tell scientists about many things: the distribution of gases in our Milky Way Galaxy, the power in the great jets of material spewing from the centers of some other galaxies, and details about magnetic fields in space. The first |
radio astronomers unexpectedly found cool
hydrogen gas distributed throughout the
Milky Way. Hydrogen atoms are the
building blocks for all matter. The remnant
radiation from the Big Bang, the beginning
of the universe, shows up in the microwave
spectrum. Infrared studies (also radio studies) tell us about molecules in space. For example, an infrared search reveals huge clouds of formaldehyde in space, each more than a million times more massive than the Sun. Some ultraviolet light comes from powerful galaxies very far away. Astronomers have yet to understand the highly energetic |