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Skywatching

A surprise in the attic

An international team of astronomers may have discovered the closest black hole to us so far.

A thousand light years away might sound like a huge distance, but in cosmic terms it is in our backyard. The object has about four times the sun's mass, and was probably once a star itself.

Massive stars can become black holes; less massive ones, neutron stars; and stars like the sun just end their lives as white dwarfs.

This object lies in the direction of the constellation of Telescopium, "The Telescope," and is only visible from the Southern Hemisphere. That is an odd name for a constellation. Our northern sky is filled up with mythical beasts and heroes from Greek, Arab and other ancient cultures. Cassiopeia, Andromeda, Hercules and Perseus are all there. There are also oddballs, such as Triangulum, "The Triangle."

The southern skies are different. Mixed in with the usual mythical characters such as Centaurus, "The Centaur" is an assortment of constellations that are definitely not of mythical origin. In addition to Telescopium, there is also Microscopium, Antlia (the pump), Fornax (the furnace), Octans (the Octant – a measuring instrument). Horologium (the clock), Circinus (the compass), Mensa (the table) and many others. Triangles are obviously important, so there is one in the southern sky too – Triangulum Australe.

The southern sky has been likened to the attic of a retired scientist. Finally, to go with a collection of old instruments in a dusty attic, there is the constellation of Musca, "The Fly."

The reason for this intriguing difference is quite simple. We, along with the Greeks, Arabs and others who set up our familiar constellations, live in the Northern Hemisphere. There is a good chunk of the southern sky that never rises above the horizon in our northern mid-latitudes, and consequently never got organized. There were some gaps that were filled later, and there was a bit of "tidying up" done later, but usually by astronomers who had a classical education.

The 18th Century was a time of a great explosion in science and the quest for knowledge. Some of that need was practical; because the world was being opened up for trade, navigation was critically important. At that time French astronomer Abbé Nicolas-Louis de Lacaille wanted to measure the distances of the planets. The method he intended to use was a common surveying technique called triangulation. He wanted to make position measurements of the planets compared with the background stars, and to do this from widely separated geographic locations. He picked as an observing site the Cape of Good Hope, near the southern tip of Africa, well south of the equator.
 
As he proceeded southward, more and more unfamiliar sky emerged above the horizon, so he filled his time with organizing it into new constellations. It was he who decided to fill the southern sky with scientific instruments.

Actually though, he was not deviating from our approach to naming constellations. The ancients wrote their contemporary culture in the sky. The culture of the 18th Century was one of an enthusiastic interest in science. Lacaille did was what the Greeks did. He put the current culture in the sky.

Today, many of the devices Lacaille put in the sky, such as the octant, are no longer used, and may indeed find their way into a dusty attic. Calling a constellation "The Table" is unusual though. It  suggests Lacaille was definitely someone with an eminently practical type of mind. 

  • Venus still dominates the western sky after sunset, but is slowly sinking back into the sunset glow.
  • Mercury is there too, but is hard to see. Mars, Jupiter and Saturn lie low in the southeast before dawn.
  • Mars lies further to the left; Jupiter and Saturn lie close together, further to the right.
  • The moon will be new on the 22nd.  


More Skywatching articles

About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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