Choosing A Telescope
Telescope Aperture Considerations
Introduction to Planetary Sketching
Refractor Dobsonian Style Mounts
The Bonds: Pioneers of American Astronomy
Saturn's Encke Minima and Encke Division
Nature and Travel Photography
Recommended Astronomy Books
Original drawing made using white pencil on black paper:
Same drawing on a white background:
July 26th/27th, 2001 11:05 PM - 12:45 AM, seeing 4-5, transparency 5.5. Also August 25th, 2001, 9:30 - 10:15 PM, seeing 4, transparency 4.0. North is at the bottom.
90mm f/5 refractor on alt-az mount. Magnification 64x to 75x. A Lumicon UHC filter was used to help bring out the fainter nebulosity.
M 17 (NGC 6618) is an Emission Nebula and Open Cluster located in the constellation of Sagittarius. The diameter of the nebula is 40' x 30', while the cluster is 25' in diameter with a magnitude of 6.0. It is approximately 4,890 light years away. M17 is known also as the Swan, Omega, or Horseshoe nebula, and was first discovered by Philippe Loys de Cheseaux in 1746. Charles Messier first observed it on June 3 1764.
Of the nebula de Cheseaux noted that it has "Perfect form of a ray or the tail of a comet."
Messier described it as a "Streak of light without stars, five to six minutes long, and rather similar to that in the belt of Andromeda, but very faint."
George F. Chambers in 1889 was the first to compare it to a swan floating on water.
William Herschel, observing it on July 31, 1783, called it "A very singular nebula; it seems to be the link to join the nebula in Orion to others, for this is not without a possibility of being stars." After observing it the following night he wrote "A wonderful nebula. Very much extended, with a hook on the preceding side; the nebulosity of the milky kind."
M 17, along with M 42, are the two brightest galactic nebula visible to observers in the mid-northern latitudes. There are fifteen Messier objects located in Sagittarius, more then any other constellation.