Hubble Space Telescope

Why a Space Telescope?

For thousands of years, the only instruments humans used to observe the universe were the eyes. These are a precious pair of antennae, very sensitive to a narrow band of wavelengths from around 380 nanometers (violet-blue light) to around 750 nanometers (red-orange light), the so-called optical band. It cannot be by chance that this is exactly the range of frequencies where our own sun emits most of its radiation, something about which Darwin's theory of evolution should have a lot to say.

Just 400 years ago, Galileo Galilei inaugurated a new era in which the instrument called the telescope would begin to aid these natural antennae in observing the sky. By progressively improving the design of telescopes, over the last four centuries astronomical observatories have flourished all around the world. Inside those often cold and uncomfortable buildings, astronomers would spend long nights, keeping their eye to the eyepiece, making use of increasingly wider and more challenging telescope mirrors.

This romantic vision of the astronomer was valid until around 50 years ago. By the beginning of the 20th century, scientists had already begun to realize that there were other bands in the electromagnetic spectrum, extending beyond the visible, but that most of them were precluded from astronomical investigation. Earth's atmosphere is actually a very effective filter with respect to the radiation coming from space. It prevents the harmful frequencies—such as X-rays, gamma rays, and even most ultraviolet light—from reaching Earth. These unexplored, invisible bands could provide astronomers with rich astrophysical information, as they would discover in the years to come.

In the 1930s, astronomers discovered another important category of waves that could penetrate the atmosphere, the so-called radio window. In 1930, the U.S. physicist and engineer Karl Jansky built the first radiotelescope (the initial goal of which was to give Bell Laboratories a way to identify noise sources that affected vocal telephone transmissions), and the era of radioastronomy began. This new discipline, developed largely after World War II, for several decades provided the source of some of the most amazing discoveries in astrophysics, including radiogalaxies, quasars, pulsars, and of course the idea of cosmic background radiation.

But things were to change only slowly. Eventually, the injection of resources by the U.S. National Aeronautics and Space Administration (NASA) made possible the development of new technology for the exploration of space and, most importantly, for the launching of satellites. It was then that the era of space telescopes really began.

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