Messier 101 (M101), also known as the Pinwheel Galaxy, is a grand-design spiral galaxy located approximately 21 million light-years away in the constellation Ursa Major. With a diameter of about 170,000 light-years, it is nearly twice the size of the Milky Way. M101's well-defined spiral arms are rich in star-forming regions, evidenced by the numerous HII regions that dot its structure. These regions are massive clouds of hydrogen gas that glow brightly due to the ionizing radiation from young, hot stars within them.

An interesting aspect of M101 is its asymmetrical shape, which is likely the result of gravitational interactions with its neighboring galaxies. This interaction has caused a distortion in its spiral arms, making them appear uneven. Additionally, M101 has a high surface brightness, making it a favorite target for amateur astronomers. Despite its beauty and prominence, M101's distance from Earth means that observing its finer details requires a telescope with good resolution and light-gathering capabilities.