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Hα was subtracted from red channel with a factor that was determined empirically such that no underflow occur. Because Hα and SII emission strongly correlate, this also eliminates some — but no all — SII light.
Furthermore green and blue channels contain OIII and Hβ emissions. This explains the colors of the bright emission nebulae that are visible in the image.
The galactic plane is parallel to the left border in the image above and the bottom border in the Javascript Viewer.
The image shows the complex galactic cirrus clouds around the celestial north pole. Polaris is the white star near the center of the image in a dense region of dust.
Almost all these reflection nebulae become visible by scattering light from the Milky Way. (That is why they are referred to as Integrated Flux Nebulae.)
Since this effect is stronger at shorter wavelengths, very dense clouds are more opaque for blue light than for (infra)red radiation.
For that reason, regions known as dark nebulae (mostly located in the constellation Cepheus) appear reddish.
Only a few small reflection nebulae in the image are illuminated by a single star or a cluster, giving them the same color as their illumination source(s).
Same view as above, but here Hα emissions are also displayed in red.
Center position: | RA: 6h, DEC: 84° |
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FOV: | 72°×48° (RA×DEC, through center) |
Orientation: | JavaScript viewer: Galactic north is top Above: Galactic north is right |
Scale: | 10 arcsec/pixel (in center at full resolution) |
Projection type: | Stereographic |
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