From the National Optical Astronomical Observatories
This picture shows the great nebula M42 (NGC 1976) in the constellation of Orion the Hunter. On a good clear night, from a dark site well away from the lights of modern civilization, this glowing cloud of gas and dust can be seen with the naked eye as a fuzzy patch surrounding the star q Orionis in the Hunter's Sword, below Orion's belt. It is probably the most spectacular of all the objects cataloged by Charles Messier . It was first noted as an extended nebula in 1610, only a year after Galileo's first use of the telescope. Detailed descriptions started appearing later in the seventeenth century, and it has been a popular target for anyone with a telescope ever since.
M42 is our closest example of an H II region, being composed mainly of ionized hydrogen which gives off the red glow so dominant in every picture of the nebula. Deep photographs such as this one show that it is nearly a degree across, larger than the full Moon . The energy to keep the nebula glowing comes from the very hot young stars in a formation called the Trapezium, embedded in the brightest part of the nebula and not visible in this photograph. The nebula and the brighter stars are very young indeed by astronomical standards, at about 30000 years. Compare this to our own Sun, which is considered to be a middle-aged star at over four billion years. M42 probably contains several hundred stars younger than a million years, still bursting with the energy of youth. Stars are still being born in a dense cloud behind the nebula, but they are hidden from our view by a concentration of dust which reduces their light to only a million-millionth of its original intensity. Fortunately, astronomers have developed special cameras and other detectors which are sensitive to infra-red radiation, more popularly known as heat, which penetrates the dust and reveals to us this stellar nursery.
Although M42 is mostly hydrogen, in both neutral and ionized states, with a fair quantity of dust, it does contain significant amounts of other elements, especially oxygen. The green glow of doubly-ionized oxygen is strongest near the intense ultraviolet starlight at the middle of the nebula. To the north-east (the upper left in this picture) is a feature called the Dark Bay, which is a thick cloud of neutral gas which has not yet been ionized.
Distance: nearly 500 parsecs (1600 light years).
Size: about 66 arcmin by 60 arcmin
Mass: about 300 solar masses.
Image Title: M42, NGC 1976, Orion Nebula
Credit: Bill Schoening/AURA/NOAO/NSF
The text is based on accompanying on-line materials.
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Last Modified On: Sunday, December 17, 2000