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M81 Galaxy by Starlight

The nearby spiral galaxy, Messier 81 (M81) is shown in this image from NASA's Spitzer Space Telescope. Located in the northern constellation of Ursa Major (which also includes the Big Dipper), this galaxy is easily visible through binoculars or a small telescope. M81 is located at a distance of 12 million light-years.

This image shows us M81 at infrared wavelengths of light at 3.6 & 4.5 microns (blue & green). At these shorter wavelengths of infrared light we are seeing the light from the stars in this galaxy, unobscured by dust that blocks our view in the visible spectrum.

M81 appears remarkably smooth in this picture, demonstrating how well-blended the populations of stars can be even in spiral galaxies. The spiral arms so visible in other parts of the spectrum are subdued and gives us a clearer picture of how stellar mass is distributed through the galaxy.