NASA's WISE mission (Wide-Field Survey Explorer) is a new spacescraft that is designed to map the sky at infrared wavelengths. The above shows a color image comet Siding Spring seen at 3-22 microns, which is rather redwards of visible light having wavelengths of ~0.6 microns. This image is colored so that the hotter stars appear blue while the much cooler cometary dust tail is red. A tail forms when the comet passes near the Sun, which warms the comet's icy surface. As the comet's icy surface sublimates (boils off), the water vapor also liberates tiny dust grains. Radiation pressure, which is the weak force that sunlight exerts on these tiny dust grains, then sweeps these particles away into a tail that can span millions of miles. See the WISE website for more details.