When Orion strides into view, you know it is a sign that winter is well under way and with it, clear, dark skies (weather permitting!) due to the decrease in atmospheric disturbance. When the air is colder, the atmosphere holds much less moisture compared to the summer months. The additional moisture probably hinders the passage of starlight. Personally, I feel sad somehow when I see Orion high in the sky to the west, a visible reminder of the passing of time perhaps?
Before taking a look at the stars in Orion, it is helpful to have a broad understanding of what a light year is in order to appreciate the vast distances involved when looking at this constellation in particular, reasons for which will become apparent. A light year is the distance light travels in a year. The speed at which it travels is 299,792 km/186,000 miles per second; it takes just over 8 minutes for light to reach us from the Sun. (Distance from Sun to Earth is around 150 million km/94 million miles) So, a light year is quite some considerable distance…10 trillion km/6 trillion miles…or
10000000000000 km/6000000000000 miles
What is a star?
A star is formed out of a collapsing cloud of interstellar matter. When the pressure and temperature become so high that nuclear reactions start, that matter becomes a star. Hydrogen is converted into helium. The force of its gravity acts as a counterbalance to the nuclear reaction and keeps the star in equilibrium. Large stars are pulled towards the base of a nebula by gravity.
Nebulae are star forming regions. Stars are formed within giant gas clouds (nebulae) where dust swirls deep within them. Pockets of gas are formed which grow so big that gravity pulls more gas into the pocket. Then gradually, the pocket of gas begins to contract, and it slowly warms up. When the pressure and temperature become so high, nuclear reactions start and the matter becomes a star.
Stars range from a mass of 0.08 to 100 (1 mass = the Sun), too small or too big and they are unsustainable.
Now onto the excitement of Orion…
M42 Orion Nebula
It is worth visiting an observatory to view this feature through a telescope. If you have 10 x 50 binoculars you will see quite a few of the features or, at least, you may catch a glimpse of the fuzzy blob with the naked eye. It is an excellent viewing target for January and February.
The Orion Nebulais a major star forming region, with four central stars in the foreground forming the Trapeziumfeature. Recent research has shown stars being formed here. It is 1344 light years away. An interesting project is to make a 3D model of Orion to demonstrate just how far the Nebula is from the main stars of the constellation. The whole area of M42 extends several hundred light years across, covering a much larger area than what is visible from Earth.
Binoculars or a telescope are appropriate for appreciating the Trapezium within the Nebula. (20 x 60 binoculars on a tripod would offer the best view). It is a multiple star system at the heart of the nebula, containing hot young stars. Within the Orion Nebula is a glow of about 30 light years across from ultraviolet radiation from the new stars forming within it.
This region also contains variable stars, ie ones that fluctuate in brightness over time. Visible through binoculars is a dark lane running east from the Trapezium. This feature, known as the Fish’s mouth which separates parts of the Nebula with the Trapezium emerging in the centre. The Horsehead Nebula is a popular image for posters although not really visible except by long exposure telescopes. It lies deep within the Orion nebula region, 1,500 light years from Earth.