OJBs Web Site: M42

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M42

Here's the basic information for M42. Its a diffuse (emission and reflection) nebula in Orion, and is also known as NGC1976 or the Orion Nebula. The position is right ascension 05:35.4, declination -05:27. The distance is about 1600 light years. The apparent magnitude is 4. The apparent size is 85x60 arc minutes, giving a true diameter of about 30 light years.

This is the brightest nebula in the sky and is visible everywhere on Earth because it is near the celestial equator. The location is easy, near the center of the bright constellation Orion. Because of this it is one of the most frequently observed objects in the sky. The nebula is really only part of a huge cloud of gas in Orion covering half of the constellation. When we look towards Orion we are looking at one of our galaxy's spiral arms which explains the gas clouds and bright, young stars.

Both stars and planets have been observed forming in the nebula. The Hubble Space Telescope has revealed this in detail. Its strange that the nebulous nature of this object wasn't mentioned before 1610 because it is so obviously not a star. M42 was the first nebula to be photographed in 1880.

Above I have attempted to show what the nebula looks like with varying size telescopes. First is the view in binoculars - quite bright and easy to see, but still just a fuzzy, oval patch. Next, a small telescope (6 to 12 inches) shows some signs of structure - the shape of the nebula we know is obvious. Finally a larger telescope (around 14 inches, or more) shows a lot of the detailed structure we see in photographs. And it always looks greenish to me, even though the true colour is red!

M42 is an object that many people can find; first because its so bright, and second because it is in the conspicuous constellation, Orion. For completeness though, I have added a finder chart above. Locate Orion - its upside down for the southern hemisphere and I show only the bottom half in the chart above.

Find the belt stars and follow the line of stars down the sword (or up the sword for southern observers). There should be a distinct fuzzy blob among the sword stars which is the nebula. This should be visible to the naked eye even if the sky isn't really dark. In binoculars it should be really easy.

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