Spiral galaxy M108

This color-composite CCD image shows the bright late-type spiral galaxy M108 (NGC 3556) in Ursa Major. This galaxy shows an especially good example of dust structure with substantial thickness in the galaxy disk; even though it is several degrees from edge-on, substantial dust shows up in front of the nuclear bulge.

This color composite is from B and I images (with synthetic V) taken during twilight with a Tektronix 2048x2048 CCD at the prime focus of the 4-meter Mayall telescope of Kitt Peak National Observatory. North is at the top and east to the left, for direct comparison with a chart or eyepiece view. The image has been block-averaged to 512x512 for this presentation, which uses a logarithmic intensity transformation to preserve information across a wide dynamic range. The field is 7.1x8.3 arcminutes. A few of the brighter field stars saturated the CCD so strongly that some of the electrical charge bled along columns, giving the vertical streaks from several stars.

M108 is easy to find telescopically, just outside the bowl of the Big Dipper close to β Ursae Majoris. It shows up in the same low-power field as the Owl Nebula (M97). This is shown in the wider-field image from the University of Alabama Crimson Dragon system below (stacking short exposures in a narrow filter around Hα).

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