Messier 100 (also known as NGC 4321) is an example of a grand design spiral galaxy located within the southern part of constellation Coma Berenices. It is one of the brightest and largest galaxies in the Virgo cluster, approximately 55 million light-years distant from Earth and has a diameter of 160,000 light years.
Several other galaxies are also visible, see finder chart below. NGC 4322 and NGC 4328 are connected to M100.
2006 Color image
2002 B&W images (with asteroid)
Full image (FOV = 35' x 23')
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The asteroid was detected by blinking between the 3 images. Here is an enlarged portion of the asteroid trace, just below IC 783:
The asteroid was easily identified on the Lowell Observatory web server which provided the following plot: