![]() ![]() Thus, a 5-m telescope will produce an image 25 times as bright as a 1-m instrument because a 5-m mirror has 5 2=25 times the collecting area of a 1-m mirror. The observed brightness of an astronomical object is directly proportional to the area of our telescope's mirror and therefore to the square of the mirror diameter. Fainter detail can be seen as the diameter of the telescope mirror increases because larger telescopes are able to collect more photons per unit time. Both photographs had the same exposure time the bottom image was taken with a telescope twice the size of that used to make the top image. Large collecting area is particularly important for spectroscopic work, as the received radiation in that case must be split into its component wavelengths for further analysis.įigure 5.10 Effect of increasing telescope size on an image of the Andromeda Galaxy. ![]() Figure 5.10 illustrates the effect of increasing telescope size by comparing images of the Andromeda Galaxy taken with two different instruments. If we wish to make detailed observations of objects far from our own cosmic neighborhood, very large telescopes are essential tools. Astronomers spend much of their time observing very distantand hence very faintcosmic sources. The larger the telescope's reflecting mirror (or refracting lens), the more light it collects, and the easier it is to measure and study an object's radiative properties. One reason for using a larger telescope is simply that it has a greater collecting areathe total area of a telescope capable of capturing radiation. The second is related to the amount of detail that can be seenthe telescope's resolving power. The first has to do with the amount of light a telescope can gatherits light-gathering power. Astronomers generally prefer large telescopes over small ones, for two main reasons. ![]()
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