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M 101

Original drawing made using white pencil on black paper:

Same drawing on a white background:

June 2-3, 2001 10:55 PM - 12:35 AM, seeing 4-5, limiting magnitude 5.3. North is at the upper left.

Astro-Physics 7.1" f/9 EDT refractor on a homemade Dobsonian-style mount. Magnification 29x to 101x.

M 101 (NGC 5457) is a spiral galaxy located in the constellation of Ursa Major. It has a magnitude is 7.9, diameter of 28.8' x 26.9', and is approximately 17.5 million light years away. It was discovered by Pierre Mechain in 1781. Messier observed it on March 27, 1781. Mechain observed it again later that year and gave the designation M102, but although he corrected this error in 1783 most astronomers were unaware of this so it became one of the missing Messier objects. The error was finally corrected in the late 1940's. M101 is known as the Pinwheel Galaxy, as is M51 and M99.

Observing it on April 14, 1789 William Herschel described it as having "Extensive nebulosity, pretty well determined on the preceding side, but very difficult to the north following".

Messier described it as "Nebula without a star, very dark and extremely large, 6 to 7 minutes in diameter, between the left hand of Bootes and the tail of Ursa Major. Difficult to distinguish when the crosshairs are illuminated."

Through the eyepiece the M101 has a relatively large, faint, irregular shape to it. At low power (29x and 53x) it almost appears to have a light green color to it, while M51 has more of a white or light blue color to it.

In M 101 three spiral arms were noted, the one at the bottom being the most prominent. At the end of this arm the HII region NGC 5462 was visible. The second most prominent arm was to the upper left, while the arm to the upper right was least prominent. In between these two arms a lighter area was noted.