With Orion well placed in the evening sky this month, lets take a look at a few of the unique objects in this well know constellation. The first stop is α Orionis, also called BetelgeuseBetelguese, α Orionis. Betelguese is a variable star and a member of a multiple star system. It is also so large that features have been observed on its surface. If Betelgeuse were to replace our Sun, it would extend out to Jupiter’s orbit. This red supergiant is an irregularly pulsing star that has a period of 5.7 years and can change its intensity by as much as a magnitude.

At the June 2009 meeting of the American Astronomical Society, it was announced that Betelgeuse is shrinking. Its diameter has reduced 15%, or roughly the distance between the orbits of Earth and VenusVenus
Courtesy of NASA, since 1993. No other red giant star has contracted as dramatically, although some Mira-type variables often contract and expand by a greater amount in the course of a year. As of this writing it is unclear why Betelgeuse has contracted, or whether it will rebound, or shrink even more.

The Great Nebula in Orion

Our next stop is ι Orionis, or Na’ir al Saif, which means simply “the Bright One of the Sword.” It is the southernmost and brightest star in Orion’s Sword and lies about 2000 lightyears away. This 15 Solar mass, O9 class giant is about 12,000 times brighter than Sol and is one of the bluest and hottest stars that make up the classic shape of Orion. ι Orionis is a complex multiple star system dominated by ι Orionis A. At a close 11″ distance is a 7th magnitude bluish B class star with a 75,000 year orbit. Further out, at 50″ in separation and a 700,000 year orbit, lies a 11th magnitude class A or F dwarf. Unseen to most telescopes without a spectrograph lies a hot B class star with a 29 day orbit with an average separation of a half an AU in an eccentric orbit that varies from 0.11 AU to 0.8 AU. Recent research has shown that Na’ir al Saif was ejected from the Trapezium
Trapezium Cluster
Image courtesy of STSci along with μ Columbae, 26° to the south and AE Aurigae, 40° to the north some 2.5 million years ago.

Along the eastern edge of Orion, between α Orionis and κ Orionis lies Barnard’s Loop
Barnard’s Loop
Copyright: Hunter Wilson. Barnard’s Loop is an emission nebula that is part of the Orion Molecular Cloud, which also contains the Horsehead Nebula
Horsehead Nebula
Courtesy of NASA and the Orion Nebula. Barnard’s Loop was thought to have originated with a supernova about 2.5 million years ago. This same supernova is thought to have ejected μ Columbae, AE Aurigae, and 53 Arietis from the Trapezium Cluster. Lying at an estimated distance of 1600 lightyears, Barnard’s Loop is nearly 300 lightyears across. The stars within the Orion Nebula are thought to be responsible for the ionization of the nebula.

To view Barnard’s Loop you will need to find transparent and dark skies. Then using your binoculars look to the east of the Orion Nebula, with a little perseverance you should be able to see a few degrees of this nebula.