The Recipe for How Hubble Makes Beautiful Color Images of Distant Galaxies

This stellar whirlpool is actually a spiral galaxy known as NGC7329, and the image shown above was taken by Hubble’s Wide Field Camera 3, or WFC3. Creating a color image like this using a telescope like Hubble isn’t as straightforward as simply pointing the camera and clicking. Commercial cameras typically try to collect most of the light at visible wavelengths in order to create the most vibrant image possible. In contrast, the raw images collected by Hubble are always monochromatic, as astronomers typically want to capture specific wavelength ranges of light to make the image as scientifically accurate as possible.

To control which wavelengths of light are collected, Hubble cameras are equipped with a wide variety of filters, which allow only certain wavelengths of light to reach the cameras CCD, the CCD is the sensor that collects the light that later it will be transformed into the final image that we can observe. Cell phone cameras currently use this same sensor.

But how are Hubble color images possible given that raw images are monochromatic? This is achieved thanks to multiple different observations that are made of the same object, which are performed using different filters. This image, for example, was processed from observations made by Hubble using 4 different filters that record different regions of the light spectrum, from ultraviolet to optical and infrared. Image processing specialists and artists can make a judgment about what colors to place for a given filter. They can then color the images using the applied filters correctly. Finally, images made with different filters are stacked, or added together. So, after all this work, we end up with a beautiful color image of a distant galaxy, with the colors being as representative of reality as possible.

Credit:

ESA/Hubble & NASA, A. Riess et al.

Source:

https://esahubble.org/images/potw2149a/