M99 — Coma Pinwheel
Galaxy in Coma Berenices
About
A grand-design spiral galaxy in Coma Berenices, roughly 45–49 million light-years away depending on the source, in the Virgo Cluster. One arm is extended and loosely wound, so it looks lopsided. A gas bridge links it to VIRGOHI21, a candidate dark galaxy. Also called the Coma Pinwheel.
Imaging tips
- About 5′ across, so it is too small to frame: use a long focal length and a fine pixel scale.
- At 22 mag/arcsec² it is faint; one published image used 260 minutes of luminance plus Hα in a 10-hour set to show the distorted arm.
- Another imager used 5 hours of 5-minute subs with no filter and a colour camera; without darks and flats it showed dust spots and vignetting, so calibrate.
- M98 is about 1.3° away, so a wide field is needed for both. Best around March and April.
Facts
- Size
- 5′ × 5′
- Magnitude
- 9.9
- Coordinates
- RA 12h 18.8m, Dec +14° 25′
- Framing, APS-C
- longer than 4000 mm
- Framing, full frame
- longer than 4000 mm
- Best months
- Mar, Apr
- Peak altitude
- 54° from 50°N, 69° from 35°N