The Rosette Nebula (NGC2237)
The Rosette Nebula is located near one end of a giant molecular cloud in the constellation
Monoceros. The open star cluster NGC 2244 is closely associated with the nebulosity and is
seen in the center of the image. The stars of this cluster are thought to have been formed from
the nebula's matter and are only a few million years old. The central cavity in the Rosette Nebula
is about 50 light-years in diameter. The cluster and nebula lie at a distance of some 5,200 light
years from Earth. Radiation from the young stars in the cluster excite the atoms in the nebula,
causing them to emit radiation which produces the emission nebula that we see.
Several images of this nebula are shown below. The grayscale image was created using a
hydrogen-alpha filter. The total exposure time was 135 minutes.
The color images were created using grayscale images from three narrow band filters for the
emission lines of H-alpha (wavelength of 656nm), SII (672nm) and OIII (501nm). These bands of
radiation come from hydrogen, sulfur and oxygen atoms in the nebula that reemit energy they
have absorbed from the surrounding starlight.
Each of these grayscale images is then assigned a primary color (red, green or blue) and then
the three are combined in Photoshop. The resulting color depends on which primary color is
assigned to what image. The so-called Hubble palette assigns green to H-alpha, blue to OIII and
red to SII. It should be noted that the resulting color images have nothing to do with reality. That
is, if you were flying by the Rosette Nebula in a spaceship, it would probably appear mostly red.
However, colorizing these images in this way makes features stand out that are not evident in the
grayscale images. Can you see any differences?
Monoceros. The open star cluster NGC 2244 is closely associated with the nebulosity and is
seen in the center of the image. The stars of this cluster are thought to have been formed from
the nebula's matter and are only a few million years old. The central cavity in the Rosette Nebula
is about 50 light-years in diameter. The cluster and nebula lie at a distance of some 5,200 light
years from Earth. Radiation from the young stars in the cluster excite the atoms in the nebula,
causing them to emit radiation which produces the emission nebula that we see.
Several images of this nebula are shown below. The grayscale image was created using a
hydrogen-alpha filter. The total exposure time was 135 minutes.
The color images were created using grayscale images from three narrow band filters for the
emission lines of H-alpha (wavelength of 656nm), SII (672nm) and OIII (501nm). These bands of
radiation come from hydrogen, sulfur and oxygen atoms in the nebula that reemit energy they
have absorbed from the surrounding starlight.
Each of these grayscale images is then assigned a primary color (red, green or blue) and then
the three are combined in Photoshop. The resulting color depends on which primary color is
assigned to what image. The so-called Hubble palette assigns green to H-alpha, blue to OIII and
red to SII. It should be noted that the resulting color images have nothing to do with reality. That
is, if you were flying by the Rosette Nebula in a spaceship, it would probably appear mostly red.
However, colorizing these images in this way makes features stand out that are not evident in the
grayscale images. Can you see any differences?
| Hubble Palette (Ha G, SII R, OIII B) |
| Ha R, SII G, OIII B |
| Ha B, SII R, OIII G |
| H-alpha image, TAK 106ED, ST10XME, external guiding Borg 77ED, 9 x 15 min exposures (click twice for full size) |