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Designations:
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M101, NGC 5457, Pinwheel Galaxy
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Object Type:
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Spiral Galaxy
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Constellation:
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Ursa Major
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14 hr 3.2 min
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+54° 21 min
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7.9
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Size:
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28.8 X 26.9 arcminutes
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Distance:
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17.5 million light years
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Discoverer:
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Pierre Mechain, 1781
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M101's numerous, far flung arms and distinct asymmetry make it readily
identifiable in photographs. Visually, its pale 9th-
magnitude
glow is diffuse and difficult to make out,
yet it has much to offer if you are patient. It is easy to locate, because you can star-hop to it from
the famous visual double star Alcor and Mizar in the handle of the Big Dipper. Southeast of this pair
is a path of four 5th-
magnitude
stars (81, 83, 84 and 86 Ursae Majoris) that leads in the direction of
M101, which lies 1½° east-northeast of 86 Ursae at the end of the trail. The
galaxy is visible
in binoculars, so try them first before taking to the telescope. Telescopically, at 23 X the
galaxy's
core is compact but slightly elliptical. Knots in phantom spirals emerge from the galactic mists, but
moderate power is much more effective in coaxing them out. Low power is best saved for determining the
full extent of the far-flung arms. High power on the other hand, is your best bet for examining the
inner region which shows a sharp nucleus inside a pentagon-shaped core. Only two arms are very definite;
beyond that everything fades out of view. You may have to alternate between moderate and low power to
preserve your sanity as you try to keep track of their directions.
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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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15 12-minute exposures for luminance and 4 15-minute exposures for each color (R,G,B). Total exposure time is 6-hours.
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Location:
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Heart of America Star Party south of Kansas City, MO
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Software:
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CCDSoft for image acquisition, processed with CCDStack and Photoshop CS2
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