Messier 81

Nearby galaxy Messier 81 is located “only” about 12 million light-years away. It is easily visible in the constellation Ursa Major through binoculars or a small telescope

This Spitzer infrared image of M81 is a composite of data at wavelengths of 3.6/4.5 µm (blue/cyan), 8 µm (green), and 24 µm (red). The “blue” data traces the distribution of stars and reveals a very smooth stellar mass distribution, with the spiral arms relatively subdued. At longer wavelengths the spiral arms become the dominant feature of the galaxy. The “green” data is mostly emissions from dust that has been heated by nearby luminous stars. Absorbing an ultraviolet or visible-light photon heats a dust grain which then re-emits the energy at longer infrared wavelengths.

Image Credit: NASA

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