M31 — Andromeda Galaxy
Galaxy in Andromeda
About
The nearest large spiral galaxy, about 2.5 million light-years away and roughly a trillion stars strong. It is approaching the Milky Way at about 110 km/s, and a merger is possible in some billions of years.
Imaging tips
- Very large: at 140–230 mm on APS-C it fits whole, with its companions M32 (24′ away) and M110 (36′ away) in the same field. Longer lenses force a mosaic.
- The core outshines the arms by a wide margin, so short single frames record little beyond it. Stack many 3–4 minute subs and use a mask to lift the arms without touching the core.
- Surface brightness is about 22.2 mag/arcsec², so total integration time matters most; several hours is a sensible start, and dark skies help.
- A light-pollution filter reduces gradients over such a large field. Best placed in September and October, when it is near the zenith in the evening.
Facts
- Size
- 178′ × 63′
- Magnitude
- 3.4
- Coordinates
- RA 0h 42.7m, Dec +41° 16′
- Framing, APS-C
- 140–230 mm
- Framing, full frame
- 210–350 mm
- Best months
- Sep, Oct
- Peak altitude
- 81° from 50°N, 84° from 35°N
Nearby
- M32 (Le Gentil) · 24.2′ away
- M110 · 36.3′ away