The Eta Carinae nebula surrounds one of the most fascinating stars. Described as 4^th magitude by Edmond Halley in 1677, it dramatically brightened in the 19^th century, becoming the second brightest star in the night sky in 1843. Subsequently, it faded again, and is currently a 6^th magnitude star.

This image is a false-color composite made through narrow-band filters at the wavelengths of [S-II] (671.9 and 673.0 nm), Hα (656.3 nm) and [O-III] (495.9 and 500.7 nm). Both the S-II and Hα wavelengths are red, while [O-III] appears green. Thus, assigning these images to the RGB color channels is completely arbitrary.

One choice, used in the famous "Pillars of Creation" image by the Hubble Space Telescope is in order of decreasing wavelength, i.e. [S-II] → R, Hα → G, [O-III] → B, also known as "SHO" mapping. Due to its strong Hα emission, the nebula appears predominantly green.

A more natural view is obtained with the "HOS" color mapping, i.e. Hα → R, [O-III] → G, [S-II] → B. The strong Hα and [O-III] emissions are both assigned to their correct color; the weaker [S-II] is responsible for the magenta cast of the outer parts of the Eta Carinae nebula.