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physical object > artifact > device > instrument > telescope > electromagnetic telescope > reflector > Gregorian

Gregorian
subject			fact

Gregorian	has secondary mirror shape concave
	has definition A class of reflecting telescope which uses a concave secondary mirror placed after the prime focus is reached instead of a convex secondary placed before the prime focus.
	has definition Telescope devised - but never constructed - by James Gregory, in which an auxiliary concave mirror reflects the magnified image, the right way up, through a hole in the centre of the main objective mirror, i.e., through the end of the telescope itself. The Cassegrain telescope is similar but produces an inverted image.
	is a kind of reflector
reflector	has mirror maker the person, company or institution that created the mirror
	has mirror type material and other engineering details
	has mirror diameter equal to aperture (except for Schmidt which has aperture smaller than mirror diameter)
	has primary mirror shape
	has aperture or primary mirror diameter
telescope	has wavelength sensitivity
	has angular resolving power
	has effective diameter
	has focal ratio
	has operator
	has purpose observe celestial objects
	has location
artifact	has creator
	has creation date
	has owner
physical object	has angular momentum
	has mass
	has velocity
	has momentum
	has temperature
	has volume
	has extent
	has material

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