Hawaiian Astronomical Society

Constellations: Libra -- Grasping the Weight of Justice

Myth

The Greeks saw Libra, perhaps the most recent constellation of the Zodiac, as the claws of the scorpion. The change from claws, while initiated by the Romans perhaps as early as the first century B.C., did not gain final acceptance as the balance scales until the Middle Ages. Sometimes the scale was associated with Astraea, Roman goddess of justice, but there is another association.

The "libra" was also a unit of weight used to balance the scale. It weighted .722 pounds (347 gm). It was abbreviated "lb.", the same as the abbreviation of the pound. The Romans used another unit of measure called the "uncia," weighing one twelfth of a libra. The "uncia" developed into the English ounce. The Anglo-Saxons referred to the constellation as either the scales or the pound.

And finally, there is spotty evidence that something other than a set of claws occupied that part of the sky before the Greeks got ahold of it.

Maps

Each map can be clicked on to produce a 929x1200 version of it. They sport red labels, which look good on screen, but which disappear when used with red flashlights. Each map, therefore has a second link to a map better suited for printing in a graphics program, and using in the field. While the maps are quite large, they are all about 25-55k, and so are easy to view at today's modem speeds. The first map is a wide area view of the constellation, suitable for naked eye browsing. The next views are binocular width, showing stars to mag. 10, and labeling deepsky objects to magnitude 12.

Interactive, wide area map of Libra

Click the map for a 929x1200 version of the above. Click here for a map better suited for use in the field.

Detailed View

This is a more detailed view of the constellation. The map displays stars to magnitude 10, and deepsky objects to magnitude 12. Click here for a map better suited for use in the field.

Images

4k GIF

35k JPEG

NGC5897 (Bennett 68) is a globular cluster located on a line drawn between Gamma and Sigma Librae. It lies somewhat closer to Sigma. Dreyer describes it as fairly faint (mag. 8.6), large (12.6'), very irregularly round, and brightening only very gradually toward the middle. Dreyer also said it was quite resolvable, meaning a 12" can perhaps resolve a few stars.

Image on the left is one of Larry's sketches made from observations through an 8" telescope. Note the irregular shape and lack of resolution. The image on the right is from the Digital Sky Survey.

Map Printable Map

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