A Brief Tour of Orion

One of my favorite regions of sky to image is around the constellation of Orion. Hiding within one of the most recognisable asterisms are: an ancient supernova remnant written large across ten degrees of the sky, dusty regions sculpted by stellar winds and radiation pressure and a plethora of star-forming regions.

This first image shows the constellation Orion below the Milky Way, which runs from middle left to the upper right corner. The Rosette nebula is on the left while the Hyades cluster is on the right, with the orange giant Aldebaran in front of them. It was taken with a kit lens at 18mm/f5.0 on a modded Canon 1100D camera. It's a slight crop, the field of view is about 40 by 55 degrees. The plate-solved image below shows Orion in relation to its neighbouring constellations.

A 50mm lens gives a closer view of the busiest region of Orion, including the seven bright stars recognisable to even the most casual stargazer.

The bright star at upper left is the red supergiant Betelgeuse. If placed at the centre of our solar system Mercury, Venus, Earth, Mars and perhaps Jupiter would be inside it. Yet despite its vast size its mass is only 10-15 that of the Sun, its tenuous outer layers being no more than hot near-vacuum.

The contrasting star at lower right is the blue supergiant Rigel, over 100,000 times brighter than the Sun. It is responsible for lighting up the dust cloud to its right known as the Witch's Head nebula, although in this orientation I think it looks like a leaping dolphin.

The nebula at the head of Orion is sometimes known as the Angelfish. Intense UV radiation from the star Meissa ionizes a could or largely hydrogen gas, causing it to glow a characteristic deep red colour.

Finally, the enormous nebula on the left of frame is Barnard's Loop. It's thought to be the result of a 2 million year old supernova, the explosion swept gas and dust into a roughly spherical shape. From our vantage point we see the left hand edge of the sphere because we are looking through a greater depth of materiel. The other side of the arc may be invisible because there was less material to be swept up in that direction, or because there are no hot stars in that vicinity to light it up. These superbubbles are fairly common, our own solar system is passing through one.

A 200mm lens gives a closer view of Orion's Belt and Sword, home to some of the most famous objects in the night sky.

Rotated 90 degrees anticlockwise from the other images, the bright star at lower left is Alnitak, the leftmost star of Orion's belt. Scattered across the frame are a collection of star-forming regions, in different stages of evolution.

The Flame Nebula on the left has a unique yellow colouration, I haven't been able to find an explanation of this. I suspect it has something to do with scattering of light by foreground dust. To its right lies the famous Horsehead Nebula, readily visible silhouetted against the bright emission nebula IC434. The Horsehead is at any early stage of star formation, a cloud of gas and dust is collapsing under gravity to form new stars which are obscured in visible wavelengths by the concentration of dust. Infra-red light is attenuated less, making it possible to peer inside the Horsehead and see these newly formed stars.

​On the right of the image lie two bright nebulae, embedded in a wider dusty region. On the left is the Running Man, a reflection nebula. To its right is the Great Nebula in Orion, M42, the closest star-forming region to Earth and easily visible to the naked eye. (I like to think of it as a great engine of possibilities, a few hundred stars are in the process of forming inside it along with associated planetary systems. Our own Sun would have been birthed in a similar nebula about 4.5 billion years ago.) M42 is in at a much later stage of evolution than the Horsehead. Intense radiation and stellar winds from the hot young stars at its core are expelling gas and dust into space, giving it the appearance of an open rose. This will bring an end to star formation in the near future, leaving behind a bright open cluster.

​These images show what is possible at the budget end of astrophotography. The first two were taken with cheap kit and 50mm lenses, a modded DSLR and a basic tracking mount. The final image was taken with a fairly expensive lens, a second hand Canon L 200mm f2.8, and a borrowed, more sturdy mount. However, similar results could have been achieved with a much cheaper optic, using a longer exposure time.