ered and recorded over a period of time than the eye can see. Glass plates covered with photographic emulsion were used with telescopes much like film is used in cameras. The longer the photographic plate was exposed, the more light was recorded. Many thousands of photographic glass plates have been produced at Lick Observatory, using the Great Lick Refractor, Carnegie Astrograph, and Shane Reflector, as well as the Crossley Reflector.
Nowadays, charge-coupled devices (CCDs) are used to record the light from observed objects which the telescope gathers, replacing both photographic plates and film. CCDs are used in home digital cameras as well as astronomical cameras and spectrographs. CCDs produce electrical charges in response to light, recording light much more sensitively than photographic emulsion. Hundreds of thousands (sometimes millions) of light-sensitive cells (pixels) cover the CCD surface. Each pixel is capable of recording many single photons, the smallest unit of light, by producing an electrical charge for each photon. Each pixel develops a total charge that represents the number of photons of light that it has detected. After an observation, a computer records the amount of electrical charge in each pixel, producing a map of the number and distribution of photons detected. This map creates a very precise, high resolution image of the object observed.
By astronomical standards, a 10 megapixel CCD is small. Astronomical CCDs in the range of 500-1000 megapixels are commonly constructed.
Because CCDs are most sensitive in the near-ultraviolet to near-infrared range, CCD cameras record mostly visible light plus some ultraviolet and infrared radiation. High-sensitivity infrared (IR) CCDs are being pioneered at UC Berkeley Labs in conjunction with Lawrence Livermore Labs, to accommodate growing interest in IR observation and imaging. These new CCDs will increase image resolution by a factor of 10.
The CCDs pictured above were built in the UCO CCD lab located at University of California Santa Cruz. Note the relative size of the quarter.
Spectroscopes analyze light by spreading it into its parts or spectrum, similar to sunlight shining through a prism. Spectrographs are spectroscopes that also produces a recorded image of the spectrum.
Spectrographs record light (using CCDs), spreading it into its constituent components, and draw a spectrum for the observed object. Spectra obtained at Lick Observatory include the visible colors plus invisible extensions, particularly infrared. The spectrum of an object shows its unique pattern of energy at each wavelength.
Dark and bright lines appear on an object's spectrum, indicating absorption and emission of energy by chemical elements within the object. By studying the size, shape, and distribution of these lines, astronomers can determine characteristics of the object such as its temperature, chemical composition, and velocity, and whether it is moving towards or away from Earth.
The spectrum of the sun above was generated by synthesizing data recorded with the Fourier Transform Spectrometer at Kitt Peak National Observatory. Image credit: N.A. Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF. Spectra of more remote stars have many more dark lines.
The turbulence of the earth's atmosphere creates an inherent problem for earth-based observations. Because the atmosphere is not uniform, pockets of varying density air bend (refract) the light from observed objects. This causes the familiar "twinkle" of stars. While poetic, this twinkling creates havoc with observations which are recorded over a period of time, in effect blurring the image.
Adaptive optics (AO) systems detect and measure how the blurring is affecting the image, and warp an auxiliary mirror to compensate for this blur. The deformable telescope mirror is almost infinitely adjustable. It changes shape in numerous places many times per second, compensating for changing atmospheric conditions to focus light precisely.
Lick Observatory engineered the first astronomical Laser Guide Star (LGS, or AO LGS) system, making adaptive op