CHAPTER 6 | LIGHT AND TELESCOPES 119
satellite was launched in 2002 and has been very productive in
the study of violent eruptions of stars and black holes. Th e
GLAST (Gamma-Ray Large Area Space Telescope), launched in
2008, is capable of mapping large areas of the sky to high
sensitivity.
Modern astronomy has come to depend on observations
that cover the entire electromagnetic spectrum. More orbiting
space telescopes are planned that will be more versatile and more
sensitive.Cosmic Rays
All of the radiation you have read about in this chapter has been
electromagnetic radiation, but there is another form of energy
raining down from space, and scientists aren’t sure where it
comes from. Cosmic rays are subatomic particles traveling
through space at tremendous velocities. Almost no cosmic rays
reach the ground, but they do smash gas atoms in the upper
atmosphere, and fragments of those atoms shower down on you
day and night over your entire life. Th ese secondary cosmic rays
are passing through you as you read this sentence.
Some cosmic-ray research can be done from high mountains
or high-fl ying aircraft; but, to study cosmic rays in detail, detec-
tors must go into space. A number of cosmic-ray detectors have
been carried into orbit, but this area of astronomical research is
just beginning to bear fruit.
Astronomers can’t be sure what produces cosmic rays.
Because they are atomic particles with electric charges, they are
defl ected by the magnetic fi elds spread through our galaxy, and
that means astronomers can’t tell where their original sources are
located. Th e space between the stars is a glowing fog of cosmic
rays. Some lower-energy cosmic rays come from the sun, and
observations show that at least some high-energy cosmic rays are
produced by the violent explosions of dying stars and by super-
massive black holes at the centers of galaxies.
At present, cosmic rays largely remain an exciting mystery.
You will meet them again in future chapters.Th e largest X-ray telescope to date, the Chandra X-ray
Observatory, was launched in 1999. Chandra orbits a third of
the way to the moon and is named for the late Indian-American
Nobel laureate Subrahmanyan Chandrasekhar, who was a pio-
neer in many branches of theoretical astronomy. Focusing X-rays
is diffi cult because they penetrate into most mirrors, so astrono-
mers devised cylindrical mirrors in which the X-rays refl ect from
the polished inside of the cylinders and form images on special
detectors. Th e telescope has made important discoveries about
everything from star formation to monster black holes in distant
galaxies (■ Figure 6-23) that will be described in later chapters.
One of the fi rst gamma-ray observatories was the Compton
Gamma Ray Observatory, launched in 1991. It mapped the
entire sky at gamma-ray wavelengths. Th e European INTEGRAL
CHAPTER | LIGHT AND TELESCOPESWhat Are We? CuriousTelescopes are creations of curiosity. You
look through a telescope to see more and
to understand more. The unaided eye is a
limited detector, and the history of astronomy
is the history of bigger and better telescopes
gathering more and more light to search for
fainter and more distant objects.
The old saying, “Curiosity killed the cat,”
is an insult to the cat and to curiosity. Wehumans are curious, and curiosity is a noble
trait—the mark of an active, inquiring mind.
At the limits of human curiosity lies the
fundamental question, “What are we?”
Telescopes extend and amplify our senses,
but they also extend and amplify our
curiosity about the universe around us.
When people fi nd out how something
works, they say their curiosity is satisfi ed.Curiosity is an appetite like hunger or thirst,
but it is an appetite for understanding. As
astronomy expands our horizons and we
learn how distant stars and galaxies work,
we feel satisfaction because we are learning
about ourselves. We are beginning to
understand what we are.■ Figure 6-23
From space, the Chandra X-Ray Observatory recorded an X-ray image of galaxy
M101. It is superimposed here on a visual wavelength image from the Hubble
Space Telescope and an infrared image from the Spitzer Space Telescope.
Blue shows hot gas around newborn stars, while red shows cool, dusty clouds
of gas. (X-ray: NASA/CSC/JHU/K. Kuntz et al.; Optical: NASA/ESA/STScI/JHU/K. Kuntz
et al.; IR: NASA/JPL-Caltech/STScI/K. Gordon)
M101