Sh2-173 — Phantom of the Opera
HII Region in Cassiopeia
About
An emission nebula in Cassiopeia, about 8,800 light-years away in the Perseus arm of the Milky Way. Dark dust lanes cutting across it give it the outline of a theatre mask, hence the Phantom of the Opera nickname.
Imaging tips
- At 810–1350 mm on APS-C (1240–2060 mm on full frame) the nebula fills a third to half of the frame.
- It is extremely faint, so expect long exposures: one imager gathered 1,020 minutes of Hα out of about 1,355 minutes across Hα, R, G and B.
- A second imager combined three small setups, mostly 10-minute Hα frames plus an RGB set for colour, and listed 5 hours 40 minutes in total.
- Best in September and October; it peaks near 78° altitude from 50°N.
Facts
- Size
- 30′
- Magnitude
- —
- Coordinates
- RA 0h 21.2m, Dec +61° 44′
- Framing, APS-C
- 810–1350 mm
- Framing, full frame
- 1240–2060 mm
- Best months
- Sep, Oct
- Peak altitude
- 78° from 50°N, 63° from 35°N