Sh2-155 — Cave Nebula
HII Region in Cepheus
About
An emission nebula in Cepheus, about 2,400 light-years away, lit by hot young stars of the Cepheus OB3 association. A bright arc of glowing gas gave Patrick Moore the cave-mouth image behind its name. Number 155 in Sharpless's list of HII regions.
Imaging tips
- Narrowband is the usual route: one write-up shot it with 3 nm Ha, SII and OIII filters, another with a dual-band Ha/OIII filter on a colour camera.
- Spans about 50′, so 480–810 mm on APS-C frames it; one imager found about 655 mm with a reducer fit it comfortably.
- Faint and slow: one imager logged over 37 hours in narrowband and wanted 50, so plan many hours, especially under light pollution.
- Best in August and September; it peaks near 77° altitude from 50°N.
Facts
- Size
- 50′
- Magnitude
- —
- Coordinates
- RA 22h 57.0m, Dec +62° 37′
- Framing, APS-C
- 480–810 mm
- Framing, full frame
- 740–1240 mm
- Best months
- Aug, Sep
- Peak altitude
- 77° from 50°N, 62° from 35°N