A measure of the blurring and degradation of the image of astronomical objects caused by turbulence in the Earth's atmosphere, including the telescope environment. Seeing causes the images of stars to
break up into speckle patterns, which change very rapidly with time.
An instrument used mainly in nautical astronomy to determine the angular distances of celestial bodies above the horizon. The sextant consists of a 60° graduated arc, or limb, a small telescope, and t
wo mirrors. Only half of one of the mirrors, the horizon glass, is silvered and, like the telescope, it is fastened to the frame supporting the limb. The other mirror, the index mirror, moves with an index arm pivoted at the center of the arc. The index arm is equipped with a vernier which moves along the limb. An object in direction S can be observed in the telescope through the un-silvered portion of the horizon glass. By moving the index arm, the second object S' is made to coincide with S in the telescope. According to the law of reflection, the angle between S and S' is double the angle between the mirrors. The angular distance between the objects can therefore be obtained from the measurement of angles between the planes of the mirrors.
The construction of a mathematical model to reproduce the characteristics of an astronomical phenomenon, system, or process, often using a computer, in order to infer information or solve problems.
The construction of a mathematical model to reproduce the characteristics of an astronomical phenomenon, system, or process, often using a computer, in order to infer information or solve problems.