M8, The Lagoon Nebula, in Sagittarius

Messier Catalog – All 110 Object Guides M8, The Lagoon Nebula, in Sagittarius

Target	Type	R.A.	Dec.	Constellation	Magnitude	Size
M8 (NGC 6523)	Bright Nebula	18h 03m 48s	-24° 23′ 00″	Sagittarius	6.00	90×40 arcmin

Overview

When you spy the Lagoon Nebula, take the time to ponder that what you’re actually seeing is a vast interstellar gas cloud.

It’s 4,000 light-years away from us and yet, under dark skies, is visible to the naked eye. This is an active star-forming region and it covers a region of space measuring 50 by 110 light-years. It, alongside the Orion Nebula, is one of only two such regions visible to the naked eye in the northern hemisphere. It is so bright because it contains extremely luminous young stars that pump radiation into it.

The Lagoon Nebula was discovered by Giovanni Hodierna in 1654, and again by John Flamsteed who independently found it in 1680. Messier observed it in May 1764 and added it to his catalog soon afterwards.

We’re not entirely sure where the name ‘Lagoon’ was minted, but it could be from an 1890 publication called The System of Stars, by Agnes M. Clerke. The name refers to the obvious dark channel that splits the nebula in two. She compared M8 to “a dark lagoon surrounded by bright fog”, very poetic.

M8 captured by Allanalaoui, is the large nebula on the right. The smaller nebula on the left is M20, the Trifid Nebula (source)

In the next section, you’ll learn how to find this lovely nebula in your own eyepiece.

Finder Charts

The first finder chart, which uses SkySafari, shows M8 high over the southern horizon at 9:30 in the evening at the end of July. Stars are shown to magnitude 5.0, but the moon and planets are not shown.

It’s easiest to find M8 using the Teapot asterism in Sagittarius, which is shown inside the left orange oval below. The right oval identifies the stinger of Scorpius the Scorpion.

[M8-1] M8 is a straightforward find once you’ve identified the Teapot asterism in Sagittarius. Click for full-screen.

In the chart below, still showing stars to magnitude 5.0, you can see the two bright stars forming the top of the Teapot’s ‘lid’ – Kaus Borealis – and its ‘spout’ – Alnasi. Between these two, you might just see a puff of ‘steam’. If you do, you’ve already found M8!

If the sky overhead is not dark enough to locate it without an aid, use binoculars or a magnifying finderscope to track it down. The chart below shows how to use the two pointer stars already mentioned to hone in on it.

[M8-2] Use Kaus Borealis and Alnasi to point the way to our nebula. Click for full-screen.

4 Sagittarii is a naked-eye star, shining at magnitude 4.7, and within one degree of the nebula, as shown by the blue circle in the chart below. The bright patch on the right hand side of the nebula, and also inside the blue circle, is 7 Sagittarii, a star shining at magnitude 5.4.

Stars in the chart below are shown to magnitude 7.

[M8-3] The blue ring shows a 1° field of view. We can fit M8 and the star 4 Sagittarii inside the same circle. Click for full-screen, or download the pdf below.

With the nebula now in your eyepiece, let’s explore what you should be seeing.

Individual Telescope Views

The following views will help you find M8 in different telescope types by presenting the images as your telescope will show them. Stars are shown to magnitude 10 and the stars 7 and 4 Sagittarii are both shown.

The first image is with a black sky and white stars, the second picture is the same image but presented in inverse monochrome. Black stars on a white background is often easier to use at the telescope. Each image can be clicked on for a full-screen version.

Upright View – This is what your eyes see unaided and through a reflex or red-dot finderscope

Upside-down view – This is what reflectors and magnifying finders show, and refractors / Cassegrains without a star diagonal

Mirrored View – Refractors and Cassegrain models with a star diagonal show this view

With this lovely galaxy now in your eyepiece, what should you expect to see?

Observation

M8 is a treat for scopes of any size, but it’s so feature-rich that it can be hard for inexperienced observers to know where to begin, particularly newcomers who are still getting to grips with the idiosyncrasies of field orientation.

Another problem is that astrophotos of M8 are typically processed to show a huge slab of pink nebulosity rich with intricate detail; a stunning sight undoubtedly, but one that can be difficult to reconcile with the telescopic view.

I find the best approach is to take it piece by piece and remember that through an undriven telescope, everything drifts to the west. So, whatever scope you use to look at M8, the bright 6th magnitude star 7 Sagittarii leads the way (see the star labeled ‘7 Sgr’ in the astro image, above).

Small Telescopes

A small telescope at low-to-medium power shows a broad expanse of nebulosity bisected by a dark lane angled southwest to northeast. The stars of the open cluster NGC 6530 glitter on the eastern side of this rift.

M8 responds particularly well to narrowband and line filters, which not only help with light pollution but also suppress the bright starlight that can overwhelm the fainter parts of the nebula.

Medium-to-Large Telescopes

As your telescope gets larger, so will the amount of detail that you can see. Remember that M8 is a massive 90 arcminutes across (three times the width of the full moon), so use your lowest-power eyepiece to get the “big picture” before switching to a higher magnification for better contrast.

In my 10-inch reflector, M8 is so large at 92x that even a 100-degree, wide field of view eyepiece struggles to contain it, but it’s a wonderfully complex region at this magnification with intense blue-white stars and bands of bright and dark nebulae competing for attention.

The nebulosity fills out considerably with the addition of a narrowband filter, revealing another patch to the south extending along the other side of the laguna into NGC 6530, and a fainter band of nebulosity to the north, separated by dark lanes.

The nebulosity becomes even more expansive through an OIII filter, filling most of the field of view (at the expense of the starlight, which is greatly subdued). The large rift dividing the cluster from the brightest part of the nebula is now a dark crescent surrounded by nebulosity on all sides, with the brightest portion transformed into a dense mottled patch of light.

At high powers (150x and above) M8 loses some of its impact, but the brightest part of the nebula is easier to study. The OIII filter shows it intensifying to a tight core that looks like it’s been pinched and twisted into shape: the distinctive Hourglass Nebula.

When you’ve finished exploring M8 the temptation is to immediately head north to M20 (the Trifid Nebula), but don’t neglect some of the other treasures nearby: NGC 6544 and NGC 6553, a pair of globular clusters southeast of M8; and – if you can see down to -28 degrees – the compact and colorful open cluster NGC 6520.

Observation guide from Dr. Alan Strauss

PDFs for Printing

Each of the star maps above is reproduced as a pdf below. Each star map has a number in [square brackets] beneath it which corresponds to the file number below. If you want image [M8-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.