Though cold winter nights might annoy some, the season’s crisp evenings most often provide clear skies, allowing us to take a joyful exploration of the sky’s constellations. Despite the large number of constellations, not all are readily visible at night, especially if you reside in a brightly lit area. As the position of the stars changes with each month, starting January until about late February, Orion will be the most distinguishable constellation in the night sky.
Commonly known in Greek mythology as the great hunter, Orion is comprised of two trapezoidal shapes conjoined by Orion’s belt. This diagonal line consists of three stars with Alnitak (Zeta Orionis) in the East, Alnilam (Epsilon Orionis) in the centre, and Mintaka (Delta Orionis) in the West.
Alnitak and Mintaka are 800 and 900 light years away respectively, and both are composed of binary or multiple star systems. While it is possible to have optical star systems (where stars may seem close because they are in the same line of sight from the Earth but, in fact, may be light-years apart) the star systems of Alnitak and Mintaka are composed of stars orbiting each other, and held together by gravity.
In contrast, the center star Alnilam is a single star 1,340 light years away, illuminating the circular interstellar gas cloud, NGC1990, more commonly referred to as a nebula. A similar gas cloud Trapezium, the Orion nebula, can be found directly underneath the belt, and is one of the few nebulae that can be observed with the naked eye.
If we were to draw a line perpendicular to Orion’s belt, in the bottom right-hand corner, you would find Rigel, Orion’s brightest star. Mythically, Rigel represents the hunter’s left foot, which is known to be composed of three distinguishable stars and a debated less luminous star, sometimes overcome by the main star’s brightness.
In the upper left-hand corner of the perpendicular line, you will find the orange-red Betelgeuse. In 2009, scientists suggested that the star’s diameter had shrunk more than 15 per cent since 1993, adding to the ambiguity of the behavior of red giants as they near the end of their lives. Since the observed shrinkage in diameter could have been caused by unidentified gas pulsations, or changes in the star’s bumpy surface as it rotates, the traditional belief remains that the radiant Betelgeuse will one day exhaust its remaining fuel and explode in a brilliant supernova.
Although both Rigel and Betelgeuse shine more brightly than the other stars composing the Orion constellation, you should not confuse them with Sirius, the brightest star in the sky (excluding the sun of course), which can be found to the south-west of the great hunter.
Orion is most visible during the first couple of months of the New Year, at around 11 p.m. on dark clear nights, in the northern hemisphere. If you find yourself strolling through the constellations around October 22, you may be fortunate enough to spot Orionids, an annual meteor shower between Orion and its northwestern neighbour Gemini.
From today’s Greek mythological hunter, son of the sea god Poseidon, we will plunge into a planet adequately named after Poseidon’s Roman counterpart next week. Until then, your next space venture awaits.
