If you go to the country, far from city lights,
you can see about 3,000 stars on a clear
night. If your eyes were bigger, you could
see many more stars. With a pair of
binoculars, an optical device that effectively
enlarges the pupil of your eye by about 30
times, the number of stars you can see
increases to the tens of thousands. With a
medium-sized telescope with a light
collecting mirror 30 centimeters in diameter,
you can see hundreds of thousands of stars.
With a large observatory telescope, millions
of stars become visible. It would seem that when it comes to observing the universe, the larger the instrument, the better. This is true up to a point, but there are limits--limits not imposed by technology but by nature itself. Surrounding Earth is a life-sustaining atmosphere that stands between our eyes and the radiations that fall upon Earth from outer space. This radiation comprises a very broad spectrum of energies and wavelengths. Collectively, they are referred to as the electromagnetic spectrum. They |
range from radio and microwave radiation
on the low energy (long wavelength) end
through infrared, visible, ultraviolet, and x-rays
to gamma rays on the high energy
(short wavelength) end. Gases and other
components of our atmosphere distort, filter,
and block most of these radiations,
permitting only a partial picture, primarily
visible radiation and some radio waves, to
reach Earth's surface. Although many
things can be learned about our universe by
studying it from the surface of Earth, the
story is incomplete. To view celestial
objects over the whole range of the
electromagnetic spectrum it is essential to
climb above the atmosphere into outer
space. From its earliest days, the National Aeronautics and Space Administration (NASA), has used the emerging technology of rockets to explore the universe. By lofting telescopes and other scientific instruments above the veil of EarthUs atmosphere, NASA has delivered a treasure house of information to astronomers, leading them to rethink their most fundamental ideas about what the universe is, how it came to be, how it functions, and what it is likely to become. |