e 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 optics more practical. Before correcting the blurring of an observed object, AO systems must measure the atmospheric distortion. Sometimes a nearby bright star can be used as a "guide star," to measure this distortion. More often, no bright star is near enough to the object to be observed. The Lick LGS system actually creates a guide "star" by shooting a laser beam into the sky, making sodium ions in the upper atmospere glow. The atmospheric distortion is measured using this manmade "star," and the deformable mirror is adjusted accordingly to get a clear view of the observed object. This system is now being used at observatories throughout the world.
Please see the Adaptive Optics webpage for more details about AO engineering and observation at Lick Observatory.
Light pollution, or light from communities and industries adjacent to observatories that reduces the accuracy of observation, is an increasing problem throughout the world today. Astronomers are increasingly interested in infrared (IR) observation, which measures wavelengths that we perceive as heat, because there is less earth-based "pollution" in this area of the spectrum. Many new IR cameras and spectrographs are being designed and built.
Mt. Hamilton is less light-polluted than many observatories, thanks to the city of San Jose. San Jose employs low-pressure sodium vapor streetlights which "pollute" only one small area of the spectrum. However, the night sky over Mt. Hamilton is even more "dark" (without interference) in the IR range.
Many astronomical processes create IR radiation that can be observed and analyzed. Examples include star formation, forming and colliding galaxies, novae and supernovae, and the event horizons of black holes. Astronomers can quantify IR radiation from around "room temperature" to several thousand degrees above absolute zero.
IR radiation also penetrates cosmic dust clouds more easily than visible light. This makes IR observation superior to visible light observation if the process itself is dusty, such as star formation Th