M20 · Trifid Nebula
| Chinese name | 三裂星云 |
|---|---|
| Type | Emission nebula |
| Constellation | Sgr |
| RA | 18h02m |
| Dec | −23° |
| Apparent magnitude | 6.3ᵐ |
| Hemisphere | Southern |
| Best season | Summer |
| Difficulty | Moderate |
| Focal length | 中长焦 800–1200mm |
About
The Trifid Nebula (M20) takes its name from the dark dust lanes that split it into several lobes, lying about 4,100 light-years away in the same crowded Sagittarius region as the Lagoon. It rarely combines three nebula types in one field: red emission, blue reflection, and the dark dust outlining their boundaries, giving striking photographic contrast. The red portion is ionized by the central multiple star HD 164492, whose young stars formed only about 300,000 years ago. The blue reflection component to the north arises from dust scattering starlight. Frequently framed with the neighboring Lagoon Nebula (M8), it is one of the most iconic medium-to-long focal targets of the summer Sagittarius sky.