A new view
Ken Tapping, May 21st, 2014
When we go out for a look at the sky on a dark, clear night, we see stars, and we see things lit up by them. Stars are very hot and make light of their own. We only see the Moon and planets because of the sunlight they reflect. Those spectacular clouds of glowing gas and dust we see in images such as those obtained using the Canada France Hawaii Telescope or the Hubble Space Telescope are only glowing because there are stars nearby. Most of the material making up the universe is cold and far from sources of light, and invisible to us.
It’s a matter of energy. You need more energy to make light than to make longer-wavelength electromagnetic radiation such as infrared or radio waves. Most of the cosmos is dark because there is not enough energy available to make light. However, in most cases there is enough energy to make infrared or radio waves. This has led to a rapid growth in the size and number of telescopes designed to operate at radio and infrared wavelengths. With these we can map and study most of the material that fills the universe between the stars. We get one other bonus; longer-wavelength radiation is less affected by the gas and dust it passes though, so we can use that to see objects that are otherwise hidden to us by clouds of foreground material. For example, the centre of our galaxy, which lies low in the south on summer evenings, is invisible to our eyes and optical telescopes by thousands of light years of clouds and dust. However infrared and radio telescopes show us the strange things lurking in the centre, which includes a large black hole.
The concentration on wavelengths of radiation that are invisible to our eyes is quite recent, and marks a big change from the astronomy we have been doing for millennia. For most of our history our ancestors observed the sky using their eyes. They might have employed astrolabes, quadrants and other devices, but the detector was the eyeball. The newly-invented telescope did not change this. It was simply a device for making the eyeball work better; it collected more light, making it possible to observe fainter things, and magnification made it easier to spot details beyond the reach of the unaided eye. When cameras were first attached to telescopes they were intended to record the things the astronomers had seen through them.
When the capability was developed to image at other wavelengths, and the value of such observations became clear, most new instruments were not optimized for visual observations. They were primarily intended as infrared tools. This movement into the infrared does not mean we are no longer interested in visual light observations. In fact, a powerful new instrument, the "Visual Survey Telescope" or VST is starting operations at a high-altitude site in Chile. It has a 2.6m mirror and as indicated in its name, is intended for making broad-field sky surveys rather than observing "objects of interest". These days there is an increasing interest in survey instruments, because we can catch many examples of the things we are studying, and are more likely to discover exciting new things.
Optical astronomy is still the main area of interest for amateur astronomers. Ever improving telescopes, cameras, computers and image processing software mean that now amateurs routinely produce images that are a quality that a decade or two ago, even professional astronomers could not achieve. So in terms of the number of people using telescopes, maybe things have not changed as much since the days of Galileo as we might have thought. The eyeball and optical observing are still the mainstream of astronomy.
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