Thus, we clearly see one of the advantages of a space telescope. Unfortunately, this result would be valid only in outer space, since the atmospheric turbulence reduces the resolving power to a value of about 2 to 3 seconds of arc near sea level or, in the best places to about 0.2 arc seconds, for example, at the top of a high mountain, where astronomical observatories are located. If the diameter is as large as 200 centimeters, the resolving power would also be large so that object details with only 0.7 arc seconds could be observed. If the diameter of the pupil is 6 millimeters as in the human eye the resolution would be one minute of arc. The main limitation for the resolution of a space telescope is the diameter of the objective. Thus, one of the main properties of a telescope, is that we can observe very small details, due to the large diameter of the main lens or mirror, called the objective. If the diameter of the eye’s pupil was ten times larger and, the light sensitive elements in the retina (cones) ten times smaller, we could see image details ten times smaller. Then, a person with a 20/20 vision can clearly see parallel lines separated by 3 centimeters at a distance of 100 meters. One minute of arc represents a 3 centimeters object size as observed from a distance of one hundred meters. This is approximately one minute of arc angular diameter. In the human eye without refractive defects (emmetropic) the resolving power is mainly limited by diffraction effects and by the size of the light sensitive elements in the retina. The resolving power depends on several factors, such as the aberrations of the optical system, the diffraction effects, which are large for small apertures of the system, the dimensions of the image elements (pixels) in the detector and atmospheric turbulence. To understand better how telescopes work, let us consider two important properties, their resolving power and their luminosity. ![]() The launch had to wait until April 25, 1990. However, the launching of the space telescope was delayed due to the tragedy of the Challenger Space Shuttle in 1986. ![]() ![]() in Danbury Conn, beginning in 1978.Įight years later, in 1985 construction of the telescope was concluded. This was done by means of a NASA contract with Perkin-Elmer Corp. It took until 1977 when the United States of America Congress approved the telescope construction to begin. The project started in 1962 when the National Academy of Sciences recommended that a space telescope be built, at a time when the space programs had not yet started. The history of the Hubble Space Telescope is full of anecdotes and problems that were satisfactorily solved over several years.
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