M8: The Lagoon Nebula
| Catalogues | M8; NGC 6523 | |
| Names | Lagoon Nebula | |
| Type | Emission Nebula | |
| Constellation | Sagittarius | |
| Season Visible in Evening | Summer; June - November | |
| Conversation Notes | Large, bright, easy to find emission nebula - huge gas cloud glowing from radiation of nearby stars. An active star-forming region, giving birth to new stars. |
An emission nebula is a huge cloud of interstellar gas, mainly Hydrogen, that is emitting light because it is fluorescing in response to being irradiated by nearby bright stars. The Lagoon nebula is a good example of this class of object (as is M42, the Orion nebula, in winter). Such huge clouds of gas are the source of new stars, as clumps of gas compress under their own gravity. M8 is actively giving birth to new stars as we watch.
Warning: It looks far better in dark skies, so save your first look for a dark sky site if that is at all possible.
Another Warning: This object is quite low in the Southern sky. From my latitude in Ottawa it is not easy to see as it is near the horizon, often obscured by trees. Observers farther north may not be able to see it at all.
Finding M8
| Start by finding the constellation Sagittarius. In late evening in August, it will be almost due South, very low in the sky. |  |
Although the official constellation is an Archer, in modern times we look for "The Teapot" - an asterism using only some of Sagittarius's stars. |
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| Practice finding the teapot in this unenhanced sky image. |  |
Now let's inspect the constellation more closely. |
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It will be useful to have names for 3 stars. Nunki is the upper outside corner of the handle. Kaus Borealis is the tip of the pointy lid. Mu Sagittarii is at the end of the line sticking out of the lid that is not part of the "teapot" asterism. |
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Imagine a straight line form Nunki to Kaus Borealis. We're going to extend that line past Kaus, into the empty space above the spout. How far to extend it? |
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The distance to extend that line is the distance from Kaus Borealis to Mu Sagittarii. |
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Extend the line from Nunki, through Kaus, the additional distance we just measured. The end of that extended line is the location of M8. |
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In very dark skies, M8 is visible to the naked eye as a dim smudge. |
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If you can't see it directly, point your telescope at the end of that extended imaginary line. |
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M8 is quite large. In dark skies, you should be able to find and centre it in your magnifying finder. If you don't have a magnifying finder, use your lowest-power, widest-field eyepiece to find and centre it. |
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In your telescope, the nebula will be a large fuzzy patch of light. With dark skies or large aperture, you will make out some internal structure. This view simulates a 4" refractor, 650mm, with a 25mm Plossl eyepiece. |
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If you have dark skies and a very wide field eyepiece, you may be able to see several objects at once. Place M8 in the far Southern edge of a very wide field, and you might see another much dimmer nebula, M20 (the Triffied nebula), and an open cluster, M21, all in the same field. This simulation shows a 100 mm f-6 refractor with a 22mm Nagler wide-field eyepiece. |
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Aren't nebulae supposed to be swirls of amazing colours? Not when viewed with your eyes - here is an explanation.
All the above images were generated with Starry Night Pro.
