One of the faint and obscure constellations
of the southern sky introduced by the Frenchman Nicolas Louis
de Lacaille after his sky-mapping trip to the Cape of Good Hope
in 1751–52. It represents the type of long, unwieldy
refractor suspended from a pole known as an aerial telescope,
as used by J. D. Cassini at Paris Observatory. The reason for
the great length was to reduce chromatic aberration (false
colour) produced by the crude lenses of that time.
Lacaille originally depicted Telescopium as
extending northwards between Sagittarius and Scorpius, as shown
on the accompanying map by Bode, but modern astronomers have
cut off the top of the telescope’s tube and mounting so
that it is now restricted to a rectangular area of sky south of
Sagittarius and Corona Australis. As a result, Lacaille’s
Beta Telescopii, positioned in the pulley at the top of the
mast, is now Eta Sagittarii, Gamma Telescopii, in the upper
part of the refractor’s tube, is G Scorpii, and
Lacaille’s Theta Telescopii, which marked the
telescope’s objective lens, is humble 45 Ophiuchi (also
known as d Ophiuchi). See here for a modern
chart of this area. Telescopium contains no stars brighter than
fourth magnitude.
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Telescopium, shown under the name Tubus Astronomicus in the Uranographia of Johann Bode, was envisaged as a long-tubed refractor operated by ropes and pulleys. For Lacaille’s original depiction, see here.
© Ian Ridpath. All rights reserved
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