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Designations:
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M104 - Sombrero Galaxy, NGC 4594
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Object Type:
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Spiral Galaxy
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Constellation:
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Virgo
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12 hr 40 min
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11° 37 min
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8 (SB 11.6)
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Size:
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8.7 X 3.5 arcminutes
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Distance:
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65 million light years
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Discoverer:
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Pierre Mechain, 1781
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Picturesque M104 is an enigma. In the 1920's Edwin Hubble began classifying
spiral galaxies based on the sizes of their central bulge relative to their arms. A
galaxy such as M74 in
Pisces, for example, has a very tight nuclear region and wide-sweeping spiral arms. M96 is on the other
side of the spectrum, with a large bulge but relatively insignificant arms. Like M96, Ml04 displays a dominant
central bulge in long-exposure photographs, but this nearly edge-on system also shows a preponderance of
interstellar gas and dust, which is characteristic of a more evolved spiral
galaxy,
somewhere between M96 and
M74 in the classification scheme. Another quizzical finding was made by Vesto Slipher of Lowell Observatory,
who in 1913 became the first astronomer to detect rotation in a
galaxy
other than our own. By studying the spectrum
of M104, he deduced that not only was the
galaxy
receding from us at 700 miles per second, but its disk was actually
rotating: one side was moving toward us while the other side was moving away from us.
You can find the Sombrero Galaxy, as M104 is aptly called, hovering about 5° northeast of Eta Corvi, just across the border in Virgo. Although it is some 20° south of the Virgo Cloud of galaxies, the Sombrero is nonetheless probably an outlying member of that group. Astronomers now believe that the galaxy is receding from us as at more than 600 miles per second and that it is extremely far away- 65 million light years. Some aficionados would prefer that the Messier catalogue end with this stunning object, perhaps feeling that the six subsequent objects (M105-M110) are visually anticlimactic by comparison. So, how does M104 look in a telescope? Through the 4-inch, low power shows the galaxy as just a tiny oval glow that begs for more magnification. And, indeed, switching to medium power makes a dramatic difference. The galaxy displays a brilliant core that seems to illuminate the surrounding oval shroud from within, like a distant bonfire seen through a thick fog. A long, bright, needlelike extension runs straight across the major axis of the oval. The sharpness of this line reveals the position of the telltale dark lane, the edge of the Mexican hat's brim. It's quite remarkable to see such detail in a galaxy with only a glance. With time the brilliant dome over the northern part of the core appears to be straddled by faint condensations, one on either side. The core is the brightest feature of the three, followed by the western knot, and then the eastern one. With averted vision the eastern portion of the Sombrero's brim breaks up and flares into a wide brushstroke of light, which shines more brilliantly than the western portion of the brim. Every now and then the lashlike dust lane wafts into view. High power should reveal the full secrets of these glimmering visions. I find the galaxy looks best at 130 x, when it changes from a misty brew of suggestions into a galaxy with tightly wound spiral arms and clumps of unresolved starlight. Most surprising is that high power shows the nucleus shining with a yellow light. I have found no other reference to this. The most challenging details lie in the southern portion of the halo, where a faint dome of light connects to the dark lane. Now switch to low power to see if you can discern a soft light enveloping the entire system. With high power can you resolve the galaxy's individual arms - crescents of light and dark that seem to ripple away from the core? With a little imagination these crescents can help you see the galaxy in three dimensions, like Saturn and its rings when they are nearly parallel to our line of sight. Few objects in the heavens allow users of small telescopes such an interesting visual perspective. |
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Telescope:
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Focal Length:
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1200 mm
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Mount:
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Camera
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Guider:
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Exposures:
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18 10-minute exposures (3 hours total)
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Location:
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Prairie Grass Observatory - near Frankfort,IN
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Software:
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CCDSoft for image acquisition, processed with CCDStack and Photoshop CS2
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