Spiral Galaxy NCG 7329 in Tucana | Hubble Space Telescope

Spiral Galaxy NCG 7329 in Tucana | Hubble Space Telescope

This stellar whirlpool is a spiral galaxy named NCG 7329. It was imaged by Hubble’s Wide Field Camera 3 (WFC3). Creating a colorful image using a telescope, such as Hubble, is not as straightforward as pointing and clicking a camera. Commercial cameras will typically try to collect as much light of all visible wavelengths as they can, in order to create the most vibrant images possible. In contrast, raw images collected by Hubble are always monochromatic, because astronomers typically want to capture very specific ranges of wavelengths of light at any time, in order to produce the best, most accurate science possible. In order to control what wavelengths of light will be collected, Hubble’s cameras are equipped with a variety of filters that only allow certain wavelengths of light to reach the cameras’ CCDs. A CCD is a camera light sensor—mobile phone cameras also have CCDs. 

How are colorful Hubble images possible given that raw Hubble images are monochromatic? This is accomplished by combining multiple observations of the same object obtained using a choice of filters. This image, for example, was processed from Hubble observations made using four filters, each of spanning a distinct region of the light spectrum—from the ultraviolet to optical and infrared. Specialized image processors and artists can make informed judgements about the optical colors that best correspond to each filter used. They can then color the images taken using that filter accordingly. Finally, the images taken with each filter are stacked together, and voila! The colorful image of a distant galaxy is complete with colors as representative of reality as possible.

Image Credit: ESA/Hubble & NASA, A. Riess et al.

Release Date: Dec. 6, 2021

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