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Triangulum Galaxy (M33)
spiral galaxy in Triangulum
The Triangulum Galaxy is the third-largest galaxy in our Local Group, and it is bigger in the sky than the full Moon. Its light is spread thin, so despite a bright total magnitude it is a dim, low-contrast target. In a long exposure it shows pink star-forming regions, including the bright NGC 604.
Save your telescope or lens on the planner to lay your camera frame over this diagram.
// Key facts
- Catalog
- M33
- Type
- spiral galaxy
- Constellation
- Triangulum
- Size
- 1.0° across
- Brightness
- Magnitude 5.7
- Distance
- about 2.7 million light-years
- Peak month (any location)
- Oct
- Typical prime months
- Jul to Dec
- Difficulty
- Advanced
- Filter
- No filter (broadband); a light-pollution filter is optional
Pick a saved location or share your device location. Your coordinates are used only to calculate tonight and are not stored. To save locations, use the planner.
How to image Triangulum Galaxy
- Light pollution is the main enemy. A dark sky makes the difference between a faint smudge and a spiral.
- Hydrogen-alpha data brings out the pink knots along the arms.
- A frame of 400 to 700 mm fits the whole galaxy comfortably.
Framing: what focal length?
The focal length at which M33 spans about 60% of the long side of the sensor, leaving room around it. Treat it as a starting point; the right framing is a matter of taste.
| Sensor | Focal length |
|---|---|
| 1-inch sensor (13.2 mm) | about 450 mm |
| APS-C (23.5 mm) | about 790 mm |
| Full frame (36 mm) | about 1220 mm |
How high does it climb from your latitude?
The highest point M33 reaches in the sky. Above about 60° is excellent, 30° to 60° is workable, and under 30° you are looking through a lot of air.
| Latitude | Highest point | Rating |
|---|---|---|
| 55°N (Scotland, Alaska) | 66° | High in the sky |
| 45°N (Minneapolis, Milan) | 76° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 86° | High in the sky |
| 25°N (Miami, Cairo) | 84° | High in the sky |
| 35°S (Sydney, Santiago) | 24° | Stays low |
Also worth imaging
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