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Hawaiian Astronomical Society

Constellations: Sextans -- Navigation before GPS


Another of Johannes Hevelius' creations, it commemorates the Sextans Uraniae, or sextant. It is an instrument with a calibrated arc, called a limb, that measures up to 60°, one sixth of a circle. Models of Hevelius' day measured the angular distance of a star (including the sun) to the horizon. Invented independently by the American, Thomas Godfry, and the Englishman, John Hadley in 1730, it teamed up with the chronometer after 1764, allowing navigators at sea to know both latitude and longitude. John Harrison perfected the chronometer's design that year in England, achieving an accuracy of .1 second per day, regardless of temperature fluctuations.


Each map can be clicked on to produce a 909x1199 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 they are quite large, they are all about 25-45k, 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, deepsky objects to mag. 12.9, and labeling deepsky objects to magnitude 12.

Interactive, wide area map of Sextans

Map thumbnail

Click the map for a 909x1199 version of the above. Click here for a map better suited for use in the field.

Detailed Map

Map thumbnail

This 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.


Image thumbnail 48k JPEG NGC3115 (Bennett 42, Best 88, Caldwell 52) is called the "Spindle Galaxy." Dreyer calls this lenticular galaxy very bright (mag. 9.7), large (8.3'x3.2'), very much elongated (P.A. 46°), and brightening sharply to a brightened, elongated nucleus. It lies 4.8° north of Lambda Hydrae. The other significant galaxy in the lower, left (south-east) of the photograph is the lenticular MCG-1-26-21 (mag. 13.5).
Map Printable Map More info.


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