Further, with more energy collected, a spectrum can be greatly dispersed and examined in much greater detail.reflectors that use lenses or mirrors, respectively, for their main light-collecting elements (objectives).

Refractors are effectively limited to apertures of about 100 cm (approximately 40 inches) or less because of problems inherent in the use of large glass lenses.

CCDs can be used for a wide range of wavelengths, from the X-ray into the near-infrared.

This restricts astronomy on Earth’s surface to the near ultraviolet, visible, and radio regions of the electromagnetic spectrum and to some relatively narrow “windows” in the nearer infrared.

Longer infrared wavelengths are strongly absorbed by atmospheric water vapour and carbon dioxide.

Accurate pointing and timing are required to permit the correlation of observations made with different instrument systems working in different wavelength intervals and located at places far apart.

The radiation must be spectrally analyzed so that the processes responsible for radiation emission can be identified.

In another technique, called Earth is a moving platform for astronomical observations.

It is important that the specification of precise celestial coordinates be made in ways that correct for telescope location, the position of Earth in its orbit around the Sun, and the epoch of observation, since Earth’s axis of rotation moves slowly over the years.

Time measurements are now based on atomic clocks rather than on Earth’s rotation, and telescopes can be driven continuously to compensate for the planet’s rotation, so as to permit tracking of a given astronomical object.

Although the human eye remains an important astronomical tool, detectors capable of greater sensitivity and more rapid response are needed to observe at visible wavelengths and, especially, to extend observations beyond that region of the electromagnetic spectrum. However, photography still provides a useful archival record.

Also, major photographic surveys, such as those of the National Geographic Society and the Palomar Observatory, can provide a historical base for long-term studies.

Photographic film converted only a few percent of the incident photons into images, whereas CCDs have efficiencies of nearly 100 percent.

For infrared wavelengths longer than a few microns, semiconductor detectors that operate at very low (cryogenic) temperatures are used.