Andromeda Galaxy vs Triangulum Galaxy
The two large spirals of the Local Group present a paradox that catches most observers out. Andromeda (M31, NGC 224) records an integrated magnitude of 3.44 against 5.79 for Triangulum (M33, NGC 598), a gap of 2.35 magnitudes worth roughly nine times the light. Yet M31 also spreads that light across 177.83 arcminutes, nearly three degrees, while M33 covers 62.09. Divide brightness by area and the two converge almost exactly: both sit near 14.4 magnitudes per square arcminute. Neither is a bright object in any meaningful sense, and both fail in the same way under a hazy suburban sky, with M33 failing slightly sooner because its lower total flux gives the eye less to work with.
Property comparison
| Property | Andromeda Galaxy | Triangulum Galaxy |
|---|---|---|
| Object type | Galaxy | Galaxy |
| Catalogue designation | NGC 224 | NGC 598 |
| Integrated magnitude | 3.44 | 5.79 |
| Apparent size | 3.0° (177.83′) | 1.0° (62.09′) |
| Mean surface brightness | 14.4 mag/arcmin² | 14.5 mag/arcmin² |
| Position (J2000) | RA 0h, Dec +41° | RA 1h, Dec +30° |
| Sky region | Northern sky | Northern sky |
Mean surface brightness is derived from the integrated magnitude and the apparent diameter; higher values mean a fainter, more diffuse surface.
Full data for each object: Andromeda Galaxy · Triangulum Galaxy
Key differences
Key Differences
- ◆ Integrated magnitude 3.44 for M31 against 5.79 for M33 — about nine times the total light.
- ◆ M31 spans 177.83 arcminutes, roughly 2.9 times the 62.09-arcminute diameter of M33.
- ◆ Mean surface brightness is near-identical at approximately 14.4 magnitudes per square arcminute for both.
- ◆ M31 lies at declination +41°, M33 at +30°; both are autumn objects for northern observers.
- ◆ M31 exceeds the field of most telescopes at low power; M33 fits a wide-field eyepiece more comfortably.