Telescopium was introduced in 1751–52 by
Nicolas-Louis de Lacaille with the French name le Telescope, depicting an
aerial telescope, after he had observed and catalogued 10,000 southern stars during a two-year stay at the
Cape of Good Hope. He devised 14 new constellations in uncharted regions of the
Southern Celestial Hemisphere not visible from Europe. All but one honored instruments that symbolised the
Age of Enlightenment. Covering 40 degrees of the night sky, the telescope stretched out northwards between Sagittarius and Scorpius. Lacaille had Latinised its name to Telescopium by 1763.
The constellation was known by other names. It was called Tubus Astronomicus in the eighteenth century, during which time three constellations depicting telescopes were recognised—
Tubus Herschelii Major between Gemini and Auriga and
Tubus Herschelii Minor between Taurus and Orion, both of which had fallen out of use by the nineteenth century.
Johann Bode called it the Astronomische Fernrohr in his 1805 Gestirne and kept its size, but later astronomers
Francis Baily and
Benjamin Gould subsequently shrank its boundaries. The much-reduced constellation lost several brighter stars to neighbouring constellations: Beta Telescopii became
Eta Sagittarii, which it had been before Lacaille placed it in Telescopium, Gamma was placed in Scorpius and renamed
G Scorpii by Gould, Theta Telescopii reverted to its old appellation of
d Ophiuchi, and Sigma Telescopii was placed in Corona Australis. Initially uncatalogued, the latter is now known as
HR 6875. The original object Lacaille had named Eta Telescopii—the open cluster
Messier 7—was in what is now Scorpius, and Gould used the Bayer designation for a magnitude 5 star, which he felt warranted a letter.