Telescopium

By BrightK self-checked Published 2026-09-04 Updated 2026-10-18 Editorial policy

• Constellations
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What is Telescopium?

Constellations· Southern winter · a faint patch south of Sagittarius. Telescopium is Lacaille's tribute to the telescope. Apart from one third-magnitude star its stars are faint, so it is remembered more for its name than its shape, and it is effectively invisible from Europe and most of North America.

Stars of the figure

The 1 brightest of the 2 stars used in the figure (1 lines). Lower magnitude means brighter.

Constellation basics

Figures are representative approximations. Source: compiled from NASA and IAU public data.

HR 6819 in Telescopium, the black hole that wasn't

In May 2020 researchers announced that a black hole was hidden inside HR 6819, a 5th-magnitude star in Telescopium. The star is about 1,000 light-years away, so if true, it would have been the nearest black hole known. It is also faintly visible to the naked eye under a very dark sky, so the news drew wide attention. The evidence was that one star seemed to circle something unseen about every 40 days.

In 2022, however, another team re-examined the same data and used sharper telescope observations to see the two stars separately. There was no black hole. Instead there was a star that had lost its outer layers to its partner, and a fast-spinning star that had taken that material. The original team accepted the result. In a constellation that honours the telescope, better telescope observations corrected an earlier conclusion.

Telescopium also produced a slow nova, RR Telescopii, in 1944. An ordinary nova brightens and fades within days. This one took months to brighten, then dimmed slowly over decades, and it has still not returned to its brightness before the outburst. It is studied as an explosion in a pair made of an old giant star and a white dwarf.

The constellation in depth

Telescopium is one of the fourteen new constellations the French astronomer Lacaille created in the 1750s while observing the southern sky from the Cape of Good Hope in South Africa. It honours the long refracting telescope, a symbol of science in his day. Lacaille placed several scientific instruments in the sky at that time, and this is one of them.

When it was first drawn, Telescopium was much larger than it is now. It overlapped a lot with its neighbours, so later astronomers trimmed it heavily when they tidied up the boundaries. Today only a small four-sided shape of faint stars remains. Astronomers in the 19th century trimmed several constellations this way, and in 1930 the International Astronomical Union fixed the boundaries of all 88.

Its brightest star, Alpha Telescopii, is a blue-white star of magnitude 3.5, about five times the Sun's mass. The constellation has few eye-catching clusters or nebulae. Delta Telescopii splits into two stars in binoculars, but they are not a real pair, just two stars in the same direction. The globular cluster NGC 6584 can be seen with a telescope.

Telescopium lies deep in the southern sky, so from New York only its alpha star rises, very low on the southern horizon, and from London none of it does; in practice it is hard to see. From the southern hemisphere it climbs high on July and August evenings. In the Sky view, set Sydney on an August evening and look below the Teapot of Sagittarius and Corona Australis.

Frequently asked

When can I see Telescopium?

Telescopium is best seen in Jul–Aug evenings; very low from New York; never rises from London.

How do I find Telescopium?

To find Telescopium, look for just south of Corona Australis, east of Ara.

What is the brightest star in Telescopium?

The brightest star in Telescopium is Alpha Telescopii, at magnitude 3.5.

Related

Figures are representative approximations. Simulated positions use J2000 mean elements.