Orion Nebula (M42)

One of the most well-known nebulae in the night sky is Messier 42. The Orion Nebula has a highly bright apparent magnitude of 4 and is the nearest significant star-forming region to Earth at barely 1,500 light-years away. M42 can be seen with the naked eye due to its brightness and prominent location directly below Orion's belt, but it also provides a fantastic view of star birth for those using telescopes. Messier 42 has an apparent size of 65 by 60 arc minutes and contains associations of stars, ionized gas, and reflection nebulae. It is popularly incorporated with its neighbor, the Running Man Nebula (NGC 1977), in photographs of this region in this sky. 

Over time as an astrophotographer, I've come to see this deep sky object as the most beautiful and intricate nebula you could possibly photograph. The Orion Nebula, Horsehead Nebula, M78, and Barnard's Loop are all included in the Orion Molecular Complex, a much bigger nebula system that spans the entire Orion constellation. Photographing the Orion Molecular Complex region of the sky with a wide aperture and short focal length telescope is one of the most rewarding nights you could have as you'll capture the world's most renowned and breathtaking celestial objects.

The Trapezium Cluster

The Trapezium Cluster is a young open star cluster in the center of Messier 42 that takes up only 47 arc seconds of the observable sky. This cluster can be seen using telescopes with 5-inch apertures, which reveal six of the cluster's stars under ideal conditions. The Trapezium Cluster could be a component of the Orion Nebula Cluster, a much more extensive cluster of over 2,000 stars spanning an area of roughly 20 light-years. The Trapezium Cluster's stars formed straight from the surrounding nebula. Within 1.5 light-years of one other, the five brightest members can be found. Their estimated masses range between 15 and 30 times that of the Sun.

The image above shows two views of the Trapezium cluster in the Orion Nebula from the Hubble Space Telescope. The image on the left is an optical spectrum photo taken with Hubble's WFPC2 camera, which shows a few stars shrouded in glowing gas and dust. The image on the right was taken with Hubble's NICMOS infrared camera, which penetrates the haze of the Orion Nebula to reveal a swarm of stars and brown dwarfs.

It's amazing to see how far technology has come since the twentieth century. Before, astronomers would take photos from their backyards with DSLR cameras. Now, we have multiple different kinds of telescopes in space, like the James Webb Telescope, equipped with various cameras which capture different aspects of the sky.

Location & Best Time to See it

The Orion Nebula is one of the brightest emission nebulae in our sky, located within the infamous constellation Orion. To spot this gem in the sky, start by finding a pair of three stars in the south that form an imperfect line. Once you've found this line, locate a trapezoid created by this line and two extremely bright stars, Rigel and Saiph. From there, you can look towards the center of this trapezoid to find the Orion Nebula. From northern latitudes, its apparent altitude reaches high enough in the southern sky for visual observation and photography. The photo below from Stellarium is a good representation of where to find the Orion Nebula in the night sky.

It is always best to view any night sky object at its peak in the sky, close to the zenith, to minimize the effects of turbulence in the air and localized light pollution. The best time to look for and photograph the Orion Nebula around the zenith is from December to April. Starting in April, Messier 42 quickly fades into the horizon in the south as the night progresses.

Photographing the Orion Nebula

Since the Orion Nebula has a remarkable apparent magnitude of 4.0 compared to other celestial bodies, almost any exposure is enough to capture the intense glow of the core and surrounding nebula. Even under moderately light-polluted skies, the entire Orion Nebula is still easily visible to the naked eye. However, as is the case with all deep-sky astrophotography targets, the key to a successful image of the Orion Nebula is an adequate amount of integration time for a healthy signal-to-noise ratio. We do this by adjusting our exposure times for each of our light frames, capturing the four main calibration frames (light, dark, flat, and bias), and finally stacking these shots together through DeepSkyStacker. A good tutorial on how to use the software is here.

Here is how to take the four main calibration frames:

Light Frames - These are your signal frames; the instructions above are how to take these.

Dark Frames - These frames' purpose is to increase your photo's signal-noise ratio. Keep the same settings you had for your light frames and cover your lens/telescope with the lid. 

Bias Frames - The purpose of these frames is to reduce the noise in your photo. Keep the same settings on your camera for your light frames, change the exposure time to the fastest it can possibly be, and cover your lens/telescope with the lid. 

Flat Frames - The purpose of these frames are to eliminate vignetting/light falloff and other artifacts in your image due to dust, dirt, or smudges on the sensor or telescope in your photo. These are tricky. In simple terms, cover your lens/telescope with a white shirt and point it at a constant light source, like the morning sky. Then experiment with the exposure times until the histogram looks like the one below. This is shown below for monochrome and color cameras.

My photo of Messier 42 below was captured using a one-shot CCD Camera (ZWO ASI294MC Pro) and a refractor telescope (100mm Aperture, 900mm focal length) with no guiding.

Orion Nebula Details:

• Messier: 42

• NGC: 1976

• Object Type: Reflection and Emissions

• Constellation: Orion

• Distance: 1344 light-years

• Apparent Magnitude: +4.0

• Apparent Size: 65 x 60 Arc Minutes

Resources:

Messier 42 - The Orion Nebula (NASA)

StarCharts - Orion Nebula

Messier Objects - Trapezium Cluster

Gallery of Orion Nebula