Cassiopeia A is the most recent supernova in the Milky Way and is among the most-studied objects in the sky. The supernova occurred ten years before the death of Spinoza and twenty years before the publication of Newton's Philosophiæ Naturalis Principia Mathematica, but it was not widely observed by astronomers of the era.
Photo credit: NASA and the Hubble Heritage Team
Featured Comment by Lawrence Siegel: "You might be interested to know that a large number of Hubble images are now on display in Baltimore's Walters Art Museum as part of a show entitled MAPS. The images are knockouts!"
Featured Comment by Thiago Silva: "It's a common misconception to assume that satellite and astronomical 'photos' are real color. In fact, 90% of the images you see are in fact composites of bands taken at different wavelength intervals, or single bands which are mapped to a color scale. Most of these images are in a spectral range invisible to us, and are assigned a 'false color' to be better interpreted by our eyes.
"A perfect real color view, right? The city is gray, the vegetation is green, the water is blue. All good, except that this image is a composite of short-wave infrared, near-infrared and red channels. The SWIR is assigned to red, because soils reflect more in that range. NIR is assigned to green, because it's where vegetation reflects the most. And the red channel is assigned to blue, since only wavelengths in the visible range penetrate water bodies. Had this image been a real color [image], the vegetation would be almost black, the waters a murky brown, and the whole image would be very foggy as most of the atmospheric interference occurs in the blue range.
"These color assignments are still grounded on knowledge about optical and electromagnetic theory, and are defined to highlight features of interest to the scientists. As our eyes can see a much larger range of color than of shades of gray, we use it as a tool to analyze images. But they are not 'artistic' choices. Some of them look more 'artistic' than others, and those probably are the ones disclosed to the press, but it is wrong to assume there is no science behind the color mapping."
Featured Comment by Simon Griffee: "Hubble site —> Behind The Pictures —> Color as a Tool."