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Optical telescopes can be classified by three primary optical designs (refractor, reflector, or catadioptric), by sub-designs of these types, by how they are constructed, or by the task they perform. They all have their different advantages and disadvantages and they are used in different areas of professional and amateur astronomy .
This is a list of U.S. weekly (or smallest available unit for time period) television ratings archives from 1948 through 1997. (Primarily Nielsen ratings) . National Nielsen ratings for United States television viewing began in March 1950.
A reflecting telescope by James Short; this English telescope maker produced almost 1400 Gregorian reflectors in the mid-1700s. Mobile versions were used to observe the Transit of Venus . List of largest optical telescopes in the 18th century includes various refractors and reflectors that were active some time between about 1699 to 1801.
The Swedish 1-m Solar Telescope, with a lens diameter of 43 inches, is technically the largest, with 39 inches clear for the aperture.The second largest refracting telescope in the world is the Yerkes Observatory 40 inch (102 cm) refractor, used for astronomical and scientific observation for over a century.
A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and astronomical telescopes but is also used for long-focus camera lenses .
The problem is that, in today's day and age, it's pretty easy to have a 12 to 14-inch refractor. There are probably hundreds if not thousands out there, and only those that are really old were "large" back in their time period, but that is now a historical note and by today's standards they shouldn't be considered "among the largest".
Between 7 a.m. and 8 a.m. Eastern time, viewership of “Morning Joe” fell 17% — from 839,000 to 694,000. In the 25-54 age demographic that is most coveted by advertisers, viewership dropped ...
Two-element refracting telescopes were extensively used in 19th century observatories despite their smaller apertures than metal, and later glass, mirror telescopes. The technology for silver-coating glass mirrors, more reflective than speculum metal and not subject to tarnishing, was developed in the mid-19th century but was slow to be adopted.
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