Orion

The Orion Nebula, catalogued as M42, appears to the naked eye as a small misty patch, making up the middle 'star' of Orion's sword. Binoculars show a little more but only hint at the sight awaiting to be discovered. To turn a telescope on this misty patch is to enter another world of:

''... stars apparently completed, shining like gems just dropped from the hand of the polisher, and around them are masses, and eddies, currents and swirls of nebulous matter yet to be condensed, compacted and constructed into suns ...'' ( G.P. Serviss).

The first telescopic observations of this wonderful region were made by Nicholas Peiresc in 1611, and the first attempt at sketching this complex nebulosity was done by Christiaan Huygens in 1656. Strangely, both observers missed M43 with it's illuminating 8 magnitude star to the north, the comma-shaped nebula, obvious to the eye, being sighted in 1731.

The Orion Nebula was also the first deep sky object successfully captured on film by Henry Draper in 1880 and the great Sir William Herschel himself began his observing career by studying this region. Sir John Herschel was the first person to study this area in depth, commencing in 1825. He wrote:

''I know not how to describe it better than by comparing it to a curdling liquid, or to the breaking up of a mackerel sky when the clouds of which it consists begin to assume a cirrus appearance...''

Sir John named the bright central area Regio Huygeniana in honour of Christiaan Huygens whom he mistakenly thought discovered M42.

The dark area near the Trapezium, separating M42 from M43, was named Sinus Magnus (the Great Gulf). It's more common name of the Fish's Mouth was adopted by W. H. Smyth in his 1844 Bedford Catalogue. The long sweeping arms of M42 were called Proboscis Major and Proboscis Minor (the Greater and Lesser Trunks), the darkness between the arms Regio Messieriana after Charles Messier.

Below the elongated black wedge of the Fish's Mouth lies the superb multiple star theta 1 Orionis, commonly called the Trapezium. It's four dazzling diamonds, wreathed in swirls of luminous gas, haunt the mind and overwhelm the senses. The C component glows brightest at magnitude 5.1 and the D star shines at magnitude 6.7. The A component is third in brightness at magnitude 6.7, however it was found to be a variable star in 1975 and fades to magnitude 7.7 every 65 days approximately. Star B is an eclipsing binary with a period of 6.5 days, fluctuating from magnitude 7.9 to 8.7.

A fifth star E was discovered by F.G.W. Struve in 1826, it's light of magnitude 11.1 almost lost in the glare of star A. Another star F, shining at 11.5, was found by Sir John Herschel in 1830 near the brightest star C. These two faint stars can be seen in telescopes of a 15cm aperture with sufficient power and fairly steady seeing conditions. Alvan Clark, observing with the 36" Lick refractor in 1888, chanced upon a very faint star G of the 16th magnitude. That same year, E. E. Barnard detected another faint star H, a double of magnitudes 15.0 and 16.0. The feeble light of these stars need very large apertures and exceptional seeing to observe at all.

In fact, there are over 300 stars brighter than 17th magnitude lying within 5' radius of Theta 1 Ori. Many are variable as are others scattered about M42. Southeast of the Trapezium lies Theta 2 Ori., a wide pair of magnitudes 5.2 and 6.5, separated by 52.5". A third companion of magnitude 9.1 lies 128.7" away.

Before we leave this immense stellar nursery, we can reflect on the words of George Bond:

''It is now impossible to see in it any other aspect than as a maze of radiating, spiral-like wreaths of nebulosity or filamentary tenticles; the centre of the vortex being about the trapezium''.

To the south of M42 lies the triple star iota Orionis, the bottom star of the sword. The nearest companion to iota is of magnitude 6.9, lying at a distance of 11.3". The third star of this system glows at 11th magnitude and lies 49.5" away. The lovely double Struve 747 lies in the same field, it's white stars shining at magnitude 4.8 and 5.7 and a wide separation of 35.7''. This whole region, centered on iota, is enveloped in the faint emission nebula NGC 1980 but only the finest of nights will show this very elusive glow.The glare of iota Orionis also tends to overpower the field.

The northern most star of Orion's sword is 42 Orionis, enclosed in the faint reflection nebulae NGC 1973-1977. A 20cm telescope in a dark sky will show these nebulae as a faint, hazy mist, a good test of the sky conditions. About 30' north lies the bright scattered open cluster NGC 1981, needing a wide field to encompass the fifty or so glittering diamonds on a black velvet background. A stunning sight and not to be missed.

Moving further north brings us to the mighty hunter's belt. The westernmost star, delta Orionis (Mintaka), shines at magnitude 2.2 and has a bluish 6.7 magnitude companion some 53" distant, directly north. Mintaka lies close to the celestial equator so makes a useful star to find out the field size of your eyepiece. Allow the star to drift through the centre of the field and the time in seconds, divided by 4 gives the diameter in arc-minutes.

Epsilon Orionis (Alnilam) is the central star of the belt and shines at magnitude 1.7. It is surrounded by the very faint nebula NGC 1990, part of the large haze which envelopes the whole constellation, which becomes visible when lit up by a bright star.

The easternmost star is zeta Orionis (Alnitak), shining at 1.79. It is a triple star with a close companion of magnitude 5.5 only 2.6" away. The other companion of 10th magnitude is easy, lying 57.6'' away but it may only be optical.

To the east of zeta Orionis lies the wonderful nebula NGC 2024, lit up into fluorescence by this extremely hot star and others hidden behind a dark dust cloud. NGC 2024 needs a dark sky and although faint, can be seen if zeta Orionis is kept out of the field. It appears as a large roundish mist with a dust lane cutting it into two. Much inner detail can be seen with larger telescopes.

To the south of zeta Orionis lies a strip of nebulosity, IC 434, which contains the dark nebula Barnard 33, more commonly called the Horsehead Nebula. This extremely difficult object needs dark, excellent conditions and averted vision to spot. It has been seen in telescopes as small as 12.5cm and missed in the largest apertures. Sky conditions play a big part in the ability to see this object.

Also south of zeta Orionis lies the roundish nebula NGC 2023 with its illuminating star of eighth magnitude. Just seen in a 20cm mirror, 30cm makes it certain.

Orion has a number of double or multiple stars and sigma Orionis is one of the best. Shining at magnitude 3.73, it is a superb example of a multiple star. The A and B components lie about 0.25" apart and can only be split in the largest telescopes. The other members are easy. The faint triple star Struve 761 lies in the same field.