How does Astronomy in Color Work?
Astronomy in Color allows you to create color images of astronomical objects from a selection of monochrome (black and white) images taken in different wavelengths of light using a variety of astronomical facilities and color filters.
Different sets of monochrome images are available for each object. The images labeled violet, blue, green, red, and far red are taken with filters that transmit a broad range of colors centered in the violet, blue, green, etc. Other monochrome images are taken using filters that transmit a narrow range of colors centered on wavelength emitted by particular atoms in hot gas. The H-alpha filter, for example, isolates hydrogen emission and indicates regions where the gas has temperatures in the range...
X-ray, gamma-ray, and ultraviolet images are taken from space telescopes designed to observe the sky in those wavelength regions. Images at radio wavelengths are obtained using radio telescopes on the ground.
Astronomers use multi-wavelength images to compare and contrast an object's appearance at several wavelengths. Stars, gas, and dust all glow in different parts of the electromagnetic spectrum. By combining images from different wavelength regions, astronomers can visualize how the gas, dust, and stars in a nebula or a galaxy interact, and can see how physical conditions vary within the object.
Natural Color - Astronomers often want to produce a natural color image that represents how the object might look to the eye. To produce a natural color image, select the available red, green, and blue monochrome images, placing the red image in the red color box, the green filter image in the green color box, and the blue filter image in the blue color box.
Pseudo-Color - To produce images of astronomical objects observed at wavelengths the eye cannot see, astronomers assign the monochrome images to be displayed as red, green or blue. For example, for the Horsehead Nebula, images in x-ray, infrared, and radio bands are available. The X-ray image could be displayed as red, the infrared image as green, and the radio image as blue. Such pseudo-color images do not portray how the object might look to the eye, but do allow astronomers to compare how the X-ray, infrared, and radio light from an object are distributed in space.
What information do we get from different wavelength regions?
Support from the National Science Foundation through the CCLI program is gratefully acknowledged.