| Historically, optical astronomy, also called visible light astronomy, is the oldest form of astronomy.[43] Optical images of observations were originally drawn by hand. In the late 19th century and most of the 20th century, images were made using photographic equipment. Modern images are made using digital detectors, particularly detectors using charge-coupled devices (CCDs) and recorded on modern medium. Although visible light itself extends from approximately 4000 Å to 7000 Å (400 nm to 700 nm),[43] that same equipment can be used to observe some near-ultraviolet and near-infrared radiation. |
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