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Messier 101 (NGC 5457)
Alastair Van Maren

Messier 101

Messier 101, also called The Pinwheel Galaxy (for obvious reasons), is a spiral galaxy that stands at a distance of about 20.9 million light years from Earth, in the constellation Ursa Major. In addition to being M101, this galaxy is also a possible candidate for M102. Both it and M102 were discovered independently by separate individuals around the year 1782. M101 was first observed and recorded by Pierre Méchain.

The reddish spots that you can see in the image above are H-II regions, which consist of a large amount of hydrogen gas gathered in one spot, heated by large nearby stars, and ready to coalesce into new stars. If you look closely, you might notice that the galaxy looks a little off-kilter, with its bulge somewhat offset from the geometric center of the galaxy. This is believed to be because of tidal interactions with other galaxies that are or have passed nearby, pulling the bulge to the side.

As stated earlier, The Pinwheel Galaxy is about 20.9 million light years away from Earth. Given its apparent size in the night sky, as seen in the image above, it is about 79,420 light years wide and across. This value, however, is off by a significant amount, because there are large portions of the galaxy that cannot be seen with the naked eye because their electromagnetic radiation is primarily in other wavelengths than are visible to us. Looking, then, at an image that makes those wavelengths visible, it becomes quite apparent that our image above shows only a fraction of the galaxy itself:

Messier 101

Image Credits: X-ray: NASA/CXC/SAO; IR & UV: NASA/JPL-Caltech; Optical: NASA/STScI

Unlike my image, this is a multi-wavelength image, including optical, x-ray, infrared, and uv light. With the exception of the optical, those wavelengths are not observable to the human eye, and in order to accommodate for this, the data from non-visible wavelengths of light has been mapped to visible wavelengths so that it is observable. The red wavlengths in this image likely coorespond to the infrared portion of the spectrum, and the blue to the UV. This makes sense because they both trace out the spiral arms, where hot gas that emits infrared radiation, and the young stars that emit UV would both be located. The purple spots are likely the remnants of supernovae and/or accretion disks around objects like neutron stars or black holes.

As you can pretty clearly see, there is much more to M101 than is visible to the human eye. There is much more going on then it might seem if we only looked at the visual light the galaxy emits. In fact, our prior observation that the center of the galaxy is off-kilter due to tidal interactions with other galaxies is even more apparent in the multi-wavelength image, as the farthest spiral arm (in the bottom right of the image) is about twice the distance away from the bulge as the spiral arms to the upper left.


"The Pinwheel Galaxy." Galaxies, NASA, 21 July 2015. Accessed 10 Apr. 2017. <>.

Immler, Stefan, and Daniel Wang. "ROSAT X-Ray Observations of the Spiral Galaxy M81." Galaxies, The American Astronomical Society, 2001,, Accessed 10 Apr. 2017.

Wikipedia, "Pinwheel Galaxy". <>

Right Ascension (J2000) 14 03 13.00'
Declination (J2000) +54 20 57.0'
Filters used B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter (s) B (300), V (300), R (300), C (300)
Image dimension 486 x 486
Date/time observed 2017-03-19 T04:33:31


Description of Data Reduction:

We used MaximDL Pro 5 for data reduction. We began by combining all the darks into a master dark, and then doing the same with the bias frames, except including the master dark into the calibrating of the master bias. We then used both the master bias and the master dark to clear out all the visual noise from our frames of a given color and produce a master frame of that color. We then combined all of these masters of a given color to produce a color image, which looked terrible. We went through and balanced the color proportions so that it looked like an actual galaxy, then adjusted the saturation to make the features of the galaxy a little more visible. We then applied the Kernel and Unsharp Mask filters, which made the whole image a lot more clear, and proceeded to clean up some dead pixels that had somehow snuck into the image. We then cropped it, and converted it into a .jpg.


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