The Illustrious Telescopium

25 Aug 2016

While waiting for my eyes to dark adapt, I was idly tracing out Telescopium’s faint and obscure shape in the sky, thinking about this obscure little constellation: no-one has placed a more important constellation among the stars than Nicolas Louis de Lacaille did when he put a telescope up there.

We owe the telescope the most illustrious position in the sky, bar none. You only have to look at the photo of Galileo’s telescope to agree that it is undoubtedly the most important piece of equipment in astronomy.  Without telescopes mankind wouldn’t have even been able to imagine, never mind begin to understand, the true nature of the universe. Without telescopes, we astronomer types couldn’t be voyaging to the stars every clear night. Without telescopes we’d be impoverished as astronomers, as human beings, as citizens of this astonishing universe.

Truly, Telescopium should be the patron constellation of astronomers… calling for strange rites, maybe the odd sacrifice or two, at culmination.

The pattern of stars that made up Lacaille’s Telescopium represented the great astronomical refractor at the Paris Observatory – known as an aerial telescope because in common with other large refractors of the day, it had an exceptionally long tube (to combat chromatic aberration) and was suspended from a mast by ropes and pulleys.

Lacaille’s telescope was equally long… it covered 40 degrees of the night sky in order to incorporate the aerial telescope’s great length – stretching out northwards between Sagittarius and Scorpius. He “borrowed” stars from nearby constellations, including Sagittarius, Scorpius, Ophiucus and Corona Australis.

But modern astronomers returned the stars to their rightful owners by hacking 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.

Thus, Lacaille’s Beta Telescopii (positioned in the pulley at the top of the mast) became Eta Sagittarii. His Gamma Telescopii (in the upper part of the refractor’s tube) became G Scorpii. And his Theta Telescopii (which marked the telescope’s objective lens) became 45 Ophiuchi.

I like the hacked down version because to me the constellation now represents Lacaille’s 8x, 26-inch-long refractor with a ½-inch objective. I am beyond flabbergasted at what he saw through his tiny refractor… and the few treasures in this little constellation that contains no stars brighter than fourth magnitude, seems a most fitting memorial to this extraordinary astronomer.

So I spent a happy while cruising around Lacaille’s telescope with my telescope.