Messier 20 - M20 - Trifid Nebula (Emission and Reflection Nebula)

M20 is the famous Trifid Nebula, a bright colourful emission and reflection nebula that's located in the constellation of Sagittarius. At magnitude +6.3, it's visible with binoculars. This remarkable object not only contains an emission and reflection nebula but also a dark nebula and an embedded open star cluster. When photographed or imaged, it looks spectacular with the emission nebula appearing red, the reflection nebula blue and mixed in between numerous dark lanes. The dark lanes appear to cut through the nebula splitting it into three prominent sections hence the popular name Trifid; meaning 'divided into three lobes'.

The much larger and brighter Lagoon Nebula (M8) is located two degrees south of M20 with tightly packed open cluster M21 positioned 0.75 degrees northeast of M20.

Charles Messier discovered both M20 and M21 on June 5, 1764. He referred to M20 as an envelope of nebulosity. The surrounding area of sky is the richest part of the Milky Way; here you are looking towards the direction of galactic centre hence the abundance of stars, open clusters, globular clusters and nebulae. This wonderful region is perfect to scan with binoculars or small telescopes, especially at low magnifications.

To locate the Trifid, first focus on the bright familiar teapot asterism of Sagittarius. The top three stars of the teapot are Kaus Borealis (λ Sgr - mag. +2.8), Kaus Media (δ Sgr - mag. +2.7) and φ Sgr (mag. +3.2). Imagine a line connecting φ Sgr to Kaus Borealis and then extending it for just over 6 degrees to arrive at M20. The Trifid is best seen from southern and equatorial regions during the months of June, July and August.

M20 The Trifid Nebula (ESO)

Finder Chart for M20 (also shown M6->M8, M18, M21->M24, M28, M54, M55, M69 and M70)

Finder Chart for M20 (also shown M6->M8, M18, M21->M24, M28, M54, M55, M69 and M70) - pdf format

Finder Chart for M9 (also shown M4, M8, M19->M21, M23, M80 and M107)

Finder Chart for M9 (also shown M4, M8, M19->M21, M23, M80 and M107) - pdf format

At magnitude +6.3, M20 is a fine sight in 7x50 or 10x50 binoculars appearing as fuzzy circular diffuse shape that's just smaller than the diameter of the full Moon. A small 80mm (3.1-inch) telescope hints at dark lanes spreading from the center of the nebula especially when viewed under dark skies. With a 150mm (6-inch) or 200mm (8-inch) scope the Trifid becomes an exciting object. Its irregular shape is visible along with the trisecting dark lanes, exquisite twists/turns and under good conditions it's possible to notice hints of colour. Of course, to really appreciate the full colour beauty of this object an image or photograph is required.

M20 is located 5,200 light-years from Earth and has a spatial diameter of 42 light-years. The dark nebula that gives the Trifid its appearance was cataloged by E. E. Barnard as Barnard 85 (B85) and in 2005 the Spitzer Space Telescope discovered 30 embryonic stars and 120 newborn stars that had not been seen in visible light images.

M20 Data Table

NameTrifid Nebula
Object TypeEmission and Reflection Nebula
Distance (kly)5.2
Apparent Mag.6.3
RA (J2000)18h 02m 21s
DEC (J2000)-23d 01m 38s
Apparent Size (arcmins)28 x 28
Radius (light years)21
Other NameCollinder 360

Sky Highlights - September 2016

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for September 2016

Mercury reaches greatest elongation west on September 28, 2016. Best chance to see the planet in the morning sky from northern locations this year.

Moon, Mars, Saturn and Antares
The Moon, Mars, Saturn and Antares close together during the evenings of September 8th and 9th, 2016

Iapetus at greatest western elongation
Saturn's bizarre two-tone moon Iapetus reaches greatest western elongation on September 9, 2016, visible in small scopes

Northern Hemisphere
West:- Venus (mag. -3.9)
Southwest:- Mars (mag. -0.3 to +0.1), Saturn (mag. +0.5)
East:- Neptune (mag. +7.8)
South:- Neptune
Southeast:- Uranus (mag. +5.7)
West:- Neptune
Southwest:- Uranus
East:- Mercury (mag. +1.5 to -0.6 last week of month)

Southern Hemisphere
West:- Venus, Jupiter (first half of month), Mercury (mag. +1.3 to +2.5 first few days of month)
Northwest:- Mars, Saturn
East:- Neptune
West:- Mars, Saturn
North:- Neptune
Northeast:- Uranus
West:- Neptune
Northwest:- Uranus

Deep Sky
Binoculars / Small telescopes:-
Messier 13 – M13 - Great Hercules Globular Cluster
Messier 57 - M57 - The Ring Nebula (Planetary Nebula)
Messier 92 - M92 - Globular Cluster
Messier 24 - M24 - Sagittarius Star Cloud
Messier 6 - M6 - The Butterfly Cluster (Open Cluster)
Messier 7 - M7 - The Ptolemy Cluster (Open Cluster)
Messier 8 - M8 - Lagoon Nebula (Emission Nebula)
Messier 27 - M27 - The Dumbbell Nebula (Planetary Nebula)

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