M8 - Lagoon Nebula in Hα

The Lagoon Nebula M8 is a straightforward emission nebula estimated to be at a distance of 4,000 to 6,000 light years from Earth. It got its name from the shape of the dark lane crossing through the its center. In M8 a lot of small dark globules, the so-called "Bok globules", which may eventually condense into stars, can be found sprinkled throughout the nebula on photographs. A cluster of young stars which is superimposed on M8 originates from the nebula. The brightest part of M8 is named the hourglass region, which was so designated by John Herschel, and shows evidence of active star formation.

The eastern (left) part of this image is dominated by extensions of the Lagoon Nebula, which are known by the following names (from top to bottom): NGC 6559, IC 1275, IC 1274, IC 4684 and IC 4685. They are combined emission and reflection nebulae and include some dark nebulae superimposed on them, most notably Barnard 303 and Barnard 91, which "snake" in front of of the red emission background.

M8 - Lagoon Nebula, which this image is part of.

Exposure Data

Instrument: 4.9" f/3.8 Wright-Newtonian with 7nm Hα filter
F/stop: 3.8
Exposure: 16 x 10 min
Camera: ATIK 383L+
Date: August 25, 2011 / August 28, 2011
Exposure start: 21:29 MESZ / 21:59 MESZ
Location: Edelweißspitze, Salzburg / Hochbärneck, Lower Austria
Conditions: SQM-L sky brightness 20.9 mag/arcsec² (decreasing), temperature 18°C, gusts of wind, low humidity / SQM-L sky brightness 20.8 mag/arcsec² (decreasing), low humidity, no wind, temperature 16°C
Autoguider: Meade Pictor 216 XT, max. error: 3" (RA) / 1" (Dec)
Enhancement: Basic data reduction, combine, logarithmic curves, local contrast enhancement, noise filtering, star size reduction
Notes: A combination of CCD exposures taken during my stay at the Großglockner-Hochalpenstraße and at the Hochbärneck in August 2011. See Observation Reports of these events (in German):Glockner 2011, Hochbärneck August 2011.

M8, the Lagoon Nebula, is located a few degrees to then north of the spout of the "teapot" which forms the constellation Sagittarius, and to the west of the main milky way stream. In a transparent night it is recognizable as big fuzzy spot and you can easily target it in your finderscope. If conditions are not so favorable and only the brightest stars of Sagittarius are visible to the naked eye, you can point the finderscope at Lambda Sagittarii in the handle of the "teapot" and move it 5 degrees west and slightly north. If you can't find it that way just go hunting for it west of the main milky way stream in your finderscope. It should be visible in the finderscope as nebulous patch of light elongated in E-W direction with about 3 stars superimposed in horizontal direction. It should be easily recognizable in the finderscope; if not, then conditions are indeed severe and observations there do not make much sense.

M8 is a fine object even in a small 2.5" refractor if you are fortunate to live far enough to the south to enjoy it higher up in the sky. For mid- northern latitudes, a 4" refractor will do fine, a 6" does show more and anyway M8 is an object which will show more and more detail the bigger your telescope is. In an 18" telescope the Lagoon Nebula can be really striking. Like with all nebulae, UHC or OIII filters do improve contrast, especially if the nebula is located low in the sky. Using one of these filters will render a ghostly green color to the nebula.

With a diameter of over 1/2 degree, a wide-field eyepiece is needed to observe the full extent of this object. The brightest parts of M8 are separated by a dark line running from the northeast to the southwest. This central dusty "channel" or "lagoon" is the source of the nebula's name. In the eastern part of the nebula the loose galactic star cluster NGC 6530 is located, which is about 10' in diameter. The west half of M8 is dominated by two bright stars, just 3' apart. The brighter star of these two is 9 Sagittarii which is already visible to the naked eye. The region immediately surrounding these brightest parts features many nebula extensions, especially to the east, northeast and north. They are observable with direct vision only in bigger telescopes, in small ones you will need averted vision as these nebula patches are extended and of low surface brightness. These parts are as well speckled with dark nebulae which render a cloudy appearance to the bright nebula segments. Within the brightest (western) part of M8, just 3' WSW of 9 Sagittarii there is situated "The Hourglass", a figure "8" shaped knot about 30" in size. This detail will take about 200x power in small telescopes and 100x in bigger ones to see well. It is in most cases more easily observable without filter. If the sky background is bright, lower magnification than that should be sufficient, especially if the hourglass region is the only nebulosity to be seen without filter.

To the south of M8 there are some globular clusters and planetary nebulae which are well observable in bigger telescopes, but you will need a good sky chart like the Uranometria to find them.