Thursday 25 June 2020

Astrognome A-Z of Constellations # 60 Orion

Orion the Hunter
Without doubt the brightest and grandest constellation in the sky, crammed with objects of interest for all sizes on instruments. Orion’s impressiveness stems from the fact that it is an area of star formation in a nearby arm of the galaxy, centred on the famous Orion Nebula.
The Orion Nebula M42 marks the hunter’s sword hanging from his belt. The belt itself is formed by a line of three bright stars. Orion is depicted as brandishing a club and shield at the snorting Taurus the Bull.
In one story the boastful Orion was stung to death by a scorpion and is now placed in the sky so he sets as the scorpion rises.
Each year the Orionid meteor shower radiates from a point near the boundary near Gemini. Around 20 meteors per hour may be seen around October 21st
Alpha Betelgeuse which means the Underarm of Orion is the 9th brightest star in the sky. It varies in brightness between 0.4-1.3 these variations were first reported in 1836 by John Herschel. When at its faintest it is decidedly fainter than Rigel. During the winter of 2019-2020 Betelgeuse became very faint causing astronomers to wonder if it was in the process of going supernova. The star has in fact been as faint as this before in 1927. It is a red giant star entering its final phase and will probably go supernova within the next 1 million years. It is 642 light years away and is a M1 class supergiant with a temperature of around 3,300’ C.
Beta or Rigel which means the left foot is the 7th brightest star in the sky at mag 0.1. It is 863 light years away, sp B8 Ia and like Betelgeux will end up going supernova, temp 12,000 degrees.
Gamma or Bellatrix which means the conqueror or Amazon star is the 3rd brightest star in Orion. It has a magnitude of 1.6, and lies at a distance of 250 light years. It is a B2 giant with a temperature of 21,500 degrees.
Zeta or Alnitak which means the Girdle is the left hand star of the belt. Alnitak has a magnitude of 2.0 and is 1200 light years distant. It is one of the rare 09 class supergiants with a temperature of 29,000’C. Alnitak will become a supernova in the future
Epsilon or Alnilam which means string of pearls at magnitude 1.6 is the 4th brightest star in Orion. Alnilam is the middle star of the belt. Its distance is about 2,000 light years, and is a B0 class supergiant with a temperature of 27,000’C.
Delta or Mintaka the right hand star of the belt its name means the belt, its magnitude is 2.2 and lies 1200 light years away, another of the rare 0.9 class stars with a temperature of 29,000’C, and as with Alnitak, Mintake will become a supernova.
Theta (one) is known as The Trapezium or Orion Trapezium Cluster is a cluster of 4 stars in the heart of the Orion Nebula they were first seen by Galileo in 1617 but he only saw 3 of the stars the fourth was discovered by several observers in 1673. The 4 stars are within 1.5 light years of each other and are responsible for much of the illumination of the surrounding nebula. The Trapezium may be a sub-component of the larger Orion Nebula Cluster, a grouping of about 2,000 stars within a diameter of 20 light-years. They have magnitudes of 5.1,6.7, 6.7 and 8.0.
Kappa or Saiph which means sword of the giant is of magnitude 2.1 and lies 650 light years away, it is a B0 class star with a temperature of 26,000’C.
Iota or Na’ir al Saif, which means "the Bright One of the Sword is the brightest star in the asterism known as the sword of Orion, Magnitude 2.8 and lying at a distance of 2,300 light years. Like many of the stars in Orion it is one of the rare 0.9 giant stars with a temperature of 32,000’C. Again iota will become a supernova in the future.
Messier 42/43
One of the great mysteries in visual astronomy is that Galileo apparently never noticed the great nebula in Orion. There also appears to be no record of it in medieval records either. Yet here is one of the grandest naked eye nebulae in the heavens just below the famous Orion belt stars. It could not possibly have been missed by Galileo and is especially puzzling. It is also interesting that the Arab astronomers including Al Sufi had recorded the much fainter nebula in Andromeda M31, the first mention in western records is around 1615.
A stellar nursery, The Orion nebula is an enormous cloud of gas about 40 light years in diameter. The cloud is illuminated by a group of four stars known as the Trapezium, these four jewels are between magnitude 5 to 8, all the stars which are very young being about 1 million years old and there are thousands of unseen stars between 300,000 to 1 million years old. The nebula is about 1600 light years away.
M43 is a separate nebula often overlooked because of its close proximity to the Great Orion Nebula, it is separated from M42 by a dark lane of gas known as the Fish Mouth. M43 surrounds a 7th magnitude star known as Bond,s star. To see M43 you have to obscure the light from M42 a good way of seeing M43 is just to gently tap the telescope tube and that slight rocking will allow you to see M43. One very well known astronomer discovered this trick while looking at the nebula when a small earthquake occurred causing the telescope to vibrate slightly.
A diffuse nebula of the 9th magnitude above and to the right of Alnitak
NGC 1977
Is an elongated nebulosity jusy north of the Orion nebula centred on the 5th mag star 42 Orionis. The object would be more celebrated if it were not overshadowed by M42.
NGC 2024
A glowing area of gas about 0.5 degrees wide surrounding the star zeta of Alnitak. Running south from Alnitak is a strip of nebulosity into which is indented the Horsehead Nebula, a dark cloud of obscuring dust shaped like a horse’s head. Although you will see the picture in many books it is notoriously difficult to see with the eye through amateur telescopes.
The Barnard Loop is the remains of a supernova that exploded about 2 million year ago. It was first photographed by Edward Barnard in 1883, it can be seen with the eye under the best of conditions. There are suggestions that it was seen by the Vikings over 1,000 years ago.

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