The Hubble palette

September 11, 2009

One of the winners of the Royal Observatory’s Astronomy Photographer of the Year contest:

[Image: Eta Carina Nebula by Thomas Davis].

Beautiful image of a nebula lying “at an estimated distance of between 6,500 and 10,000 light years away.” The photographer mentions that narrowband filters have been applied to the image (the “Hubble palette”). Although I’d heard the term before, I didn’t quite know what that was, so I dug a little further:

You can even use different spectral lines to represent different colors. That is often done to produce the amazing images that you see from professional observatories or space based telescopes. It is important to note that these are virtually always false color images. A common color scheme is the Hubble palette (since many HST images are released using it). The Hubble palette is what Steve Tuttle used in the image at the top of this posting. The Hubble palette uses images from three narrow line filters, S II [ionized sulfur], Hα [hydrogen alpha], and O III [doubly-ionized oxygen], to be the red, green, and blue parts of the image.

Two slightly different red images make up the red and green parts of the image, and a green image makes up the blue part of the image (thanks to the wonders of computer processing). So, effectively, about half of the visual spectrum is stretched in color to cover the whole spectrum. But, the images produced in this manner are quite spectacular and very pretty. For this reason, they have been widely circulated, and so many people are familiar with how many celestial objects appear in this color scheme. But, many astrophotographers don’t really like the Hubble palette, because the images don’t look anything at all like the old images taken with film cameras.



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