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Which parts of the electromagnetic spectrum can ground-based telescopes observe most easily?
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Telescope
Aerial view of the Keck Observatory's twin domes, which are opened to reveal the telescopes. Keck II is on the left and Keck I on the right.
Ground-based telescopes are restricted by the Earth's atmosphere, which does not transmit all wavelengths of electromagnetic radiation equally well. Consequently, ground-based observations are primarily limited to the following regions of the electromagnetic spectrum:
- Visible light: The range to which the human eye is sensitive.12
- Radio waves: Observations in this region are highly effective, and arrays of radio telescopes can achieve high angular resolution.13
- Near ultraviolet: Some observations are possible in this region, though it is limited by atmospheric absorption.1
- Near infrared: Observations are restricted to relatively narrow "windows" in the spectrum, as longer infrared wavelengths are strongly absorbed by atmospheric water vapour and carbon dioxide.1
Because the atmosphere is opaque to much of the spectrum—including most ultraviolet, X-ray, and gamma-ray radiation—astronomers must often use spacecraft or high-altitude platforms to observe these wavelengths effectively.14