How to Find and Observe the Trifid Nebula (M20)

M20, also known as the Trifid Nebula, is a stunning summertime object, impressive to observe through any instrument. Located in a dense region of the Milky Way, this nebula is truly the trifecta, containing emission, reflection, as well as dark nebulae.

As you read through this article you will learn how to locate and observe M20 with the naked eye, as well as through binoculars and a telescope. You will also note the nearby Lagoon Nebula and cluster, which Mark wrote the guide for, and the open cluster Messier 21.

M20 Vital Statistics

What is Messier 20?

M20, broadly speaking, is a stellar nursery – a large embryonic molecular cloud of (mainly hydrogen) gas and dust that is giving birth to new stars.  It is a particularly striking object in photographs, such as the image below.

Looking at the image, you can see the bright ‘emission nebula’ glowing red. This red glow is the result of radiation being emitted from the hot young stars being born in the nebula and ionizing the surrounding gas.

The blue glow that you see is a ‘reflection nebula’, as the gas and dust of the molecular cloud is reflecting the light of nearby stars and is not being directly ionized. 

The darker regions and lanes that you see twisting across the glowing nebula (and appearing to separate the emission nebula into four sections) are dark nebulae – or regions of dust that are obscuring the glow of the emission and reflection nebula from our view.  

The name Trifid comes from Latin and means three-lobed, and was given to M20 by John Herschel despite his father William noting the fourth faint lobe.

Discovered by Guillaume Le Gentil in 1747, Messier rediscovered this nebula on 5 June 1764 and wrote “Star cluster, slightly above the ecliptic, between the bow of Sagittarius and the right foot of Ophiuchus.”

I find it surprising that his description does not mention either the nebulosity or the other exceedingly close Messier objects that fit in the same low power field of view of binoculars or a telescope.

Read on to learn just how beautiful this object and region of the Milky Way are, and to observe the three types of nebulae contained in M20.

When is M20 Visible?

This table shows when you can best see M20 from the mid-latitudes of the northern hemisphere. Times given are approximate local times for mid-month using a 24hr clock. Underlined times are during the hours of darkness.

Seeing Conditions Needed to See M20

M20 sits within a 1.5-degree circle together with M8 (the Lagoon Nebula) and the open cluster M21. Together, the glow from these three objects is visible to the naked eye as a bright knot in the Milky Way from Bortle 4 skies.

At magnitude 6.3, the glow of M20 should be visible in binoculars under Bortle 5-6 skies, and through a small telescope under Bortle 7 skies. 

As this cluster is located in the southerly constellation of Sagittarius, I recommend a location with a darker southern horizon, near the time of its transit. From my home in Southern Arizona with a latitude of ~32 degrees north, M20 never rises higher than about 34°.

You will need to consider your own observing location for the best views of this nebula. Use free stargazing software like Stellarium to work out when and where to look for M20 in your location.

How to Find M20

Popular atlas references:

• Sky and Telescope’s Pocket Sky Atlas: Pg. 67
• Sky Atlas 2000: Chart 22 

Finding M20 is fairly straightforward. Use the SkySafari 6 charts below, which can be clicked on for full-screen versions, to find it for yourself.

To begin, face south and identify the constellation of Scorpius and the ‘teapot’ asterism of Sagittarius. If you can faintly see the milky way, you will notice a glowing patch just above the spout of the teapot.

This glowing patch is the combined light of M8, M21, and our target M20.  I like to think of this whole region north of the teapot as the ‘steam’ emanating from the spout.

If you can not see the glow of the Milky Way, use the chart below and take your binoculars or telescope at low power (try and achieve a 2-degree field of view, shown by the blue circles, you will not be disappointed) and point at the northern star of the teapot’s lid, Kaus Borealis. 

Now, imagine a line that joins Phi Sagittarii at the bottom left of the ‘lid’ to Kaus Borealis (shown orange in the image below). Continue that line northwesterly for about 6°.

As you pan your view to the north and slightly west, you should notice the glow of M8 first and then the fainter glow of M20 just above, and the small open star cluster M21 just to the east of M20.

All three of these Messier objects fit within the same 2° circle of the second star map, which gives you a sense of how close together they are.

Before proceeding, take a moment to appreciate that good things come in threes, as the view of these three objects together is one of the finest summer sights.  

What M20 Looks Like in a Telescope

Binoculars

While M20 is easily visible in binoculars, it is the entire complex of M20, M8 and M21 which is most impressive. My favorite binoculars for stargazing are 7 x 50s, and they provide an excellent widefield context for these objects. M20 is visible in even smaller binoculars, depending on your skies, and I have seen it in my 8.5 x 21 pair.   

Small Telescopes

Observing M20 through a small telescope is a treat!

To begin, use your lowest power eyepiece and again take in the view of M20 along with its neighbors. There are not many areas in our night sky that contain such beauty, and it is worth appreciating the whole area before focusing on the target object.  As the saying goes, ‘Do not lose the forest through the trees!’

Slowly increase the magnification of your telescope and begin to look for all three types of nebula – emission, reflection, and dark. The emission nebula is brightest and should be readily apparent. At 80 – 100 power, note that the star nearest the center of the emission nebula is a double star.

As you continue to observe, you should begin to notice the lanes of dark nebula separating the lobes of M20. The reflection nebula is less obvious, yet is prominent north of the central emission nebula.

In terms of the star cluster forming within M20, you should be able to see about a dozen of the 50 or so loosely associated stars in a small telescope.

If you have a nebula or contrast filter, try it out on this object – it may enhance the views depending on your local circumstance and observing experience. Check out this article for more information on these different filters.

Can you see all three types of nebulae?  If so, congratulations, you hit the Trifid Trifecta!

Large Telescopes

While you have appreciated its context and seen the major features of this nebula through a small telescope, observing M20 through a large telescope is an opportunity not to be missed.

In my 12.5-inch Dobsonian, I am drawn to the dark lanes that criss-cross the nebula and enjoy exploring the boundaries between the dark and bright nebula in M20. As you explore these intricate and ethereal details, try and notice the faint 4th lobe of the nebula.

The longer you spend observing, the more subtle detail you will see along the edges of the dark nebular lanes. Instead of a smooth edge, you will begin to notice a more uneven boundary and you may note a general mottling across the emission nebula itself. 

The reflection nebula is nearly the size of the emission – how much can you detect?  Can you note any small dark nebular globules in other areas besides the lanes that create the Trifid’s signature lobes?

Summary

I hope that you enjoyed locating and observing M20 and its glorious environs.

As I was observing M20 while writing this article, I started to wonder whether it is part of the same molecular cloud as M8. As it turns out, astronomers have explored this exact question and they have determined that, while at similar distances from Earth, M20 and M8 are indeed separate nebulae. 

Leave us a comment below and let us know what thoughts, ideas, questions, or experiences you had while finding and observing M20.