4.1 Introduction

There are three basic components of a modern system for measuring radiation from astronomical sources. First, there is a telescope, which serves as a “bucket” for collecting visible light (or radiation at other wavelengths, as shown in Figure 4.1. Just as you can catch more rain with a garbage can than with a coffee cup, large telescopes gather much more light than your eye can. Second, there is an instrument attached to the telescope that sorts the incoming radiation by wavelength. Sometimes the sorting is fairly crude. For example, we might simply want to separate blue light from red light so that we can determine the temperature of a star. But at other times, we want to see individual spectral lines to determine what an object is made of, or to measure its speed . Third, we need some type of detector, a device that senses the radiation in the wavelength regions we have chosen and permanently records the observations.

Orion Region at Different Wavelengths

Three images of the constellation of Orion in different wavelengths of light. On the left (a) is a visible light image, with straight lines connecting the bright stars to form the outline of the constellation, which is that of a man. Below the three stars that form Orion’s belt in the center of the image is the famous Orion nebula. Image (b) shows the same area in X-rays. As only a few of the stars seen in visible light are seen in X-rays, the outline of the constellation has been omitted. Numerous very bright stars and other distant sources are prominent. Lastly, on the right (c), is an infrared image. Some of the stars are visible, so the outline is again presented. The image is nearly covered with delicate wisps of nebulosity which get quite bright and dense in the vicinity of the Orion nebula.
Figure 4.1. The same part of the sky looks different when observed with instruments that are sensitive to different bands of the spectrum. (a) Visible light: this shows part of the Orion region as the human eye sees it, with dotted lines added to show the figure of the mythical hunter, Orion. (b) X-rays: here, the view emphasizes the point-like X-ray sources nearby. The colours are artificial, changing from yellow to white to blue with increasing energy of the X-rays. The bright, hot stars in Orion are still seen in this image, but so are many other objects located at very different distances, including other stars, star corpses, and galaxies at the edge of the observable universe. (c) Infrared radiation: here, we mainly see the glowing dust in this region. (credit a: modification of work by Howard McCallon/NASA/IRAS; credit b: modification of work by Howard McCallon/NASA/IRAS; credit c: modification of work by Michael F. Corcoran; CC-BY-4.0)

Attribution

“6.1 Telescopes” from Douglas College Astronomy 1105 by Douglas College Department of Physics and Astronomy, is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. Adapted from Astronomy 2e.

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Fanshawe College Astronomy Copyright © 2023 by Dr. Iftekhar Haque is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.