Soul Nebula (Westerhout 5)

The Soul Nebula is a massive star-forming complex that is part of the Perseus spiral arm of our Milky Way galaxy and is situated around 6,500 light-years from Earth. Compared to the component that houses our sun, the Perseus arm is located farther from the Milky Way's core. As a result, a small piece of the Milky Way's diameter, around 100,000 light-years across, is covered by the Soul Nebula, which spans nearly 580 light-years.

The Soul Nebula is home to several open clusters of stars, ridges and pillars darkened by cosmic dust, and giant evacuated bubbles carved out by the stellar winds from the stars embedded within it. These pillars are very dense and have stars forming at their tips. Each pillar spans about ten light years. The image above was taken using SHO narrowband filters and assigning each filter's wavelength to a different color using the Hubble Palette. The Hubble Palette consists of the following primary color assignments: 

Sulfur-II: Red | Hydrogen-Alpha: Green | Oxygen-III: Blue 

Using this Palette, astronomers and astrophotographers can reveal details of objects in space that the human eye cannot easily see, if at all, with the natural colors of each gas.

The Great Rift in the Soul

The two clouds of gasses that make up the Soul Nebula are connected through a bridge-shaped gas formation called the Great Rift in the Soul. The Great Rift is a dense interstellar cloud that blocks light from the nebula's glowing gas and stars, creating a striking contrast between the bright and dark regions. The Great Rift is an excellent example of how interstellar dust can shape and obscure our view of the cosmos, adding a sense of mystery and depth to the universe.

"This cosmic close-up looks deep inside the Soul Nebula. The dark and brooding dust clouds on the left, outlined by bright ridges of glowing gas, are cataloged as IC 1871. About 25 light-years across, the telescopic field of view spans only a small part of the much larger Heart and Soul nebulae. At an estimated distance of 6,500 light-years the star-forming complex lies within the Perseus spiral arm of our Milky Way Galaxy, seen in planet Earth's skies toward the constellation Cassiopeia. An example of triggered star formation, the dense star-forming clouds of IC 1871 are themselves sculpted by the intense winds and radiation of the region's massive young stars. The featured image appears mostly red due to the emission of a specific color of light emitted by excited hydrogen gas." 

NASA, APOD - November 28, 2018

Location & Best Time to See it

The Soul Nebula is one of the largest nebulae in the night sky. To observe it yourself, start by locating where Northeast is and finding the constellations Cassiopeia, Camelopardalis, and Perseus. Once you have found them, Westerhout 5 should be located near the center of the space between these three constellations. The photo below from Stellarium is a good representation of where to find the Soul Nebula in the night sky.

The Soul Nebula is usually visible in the night sky for most of the year, but the best time to look for it from this latitude is from September – December when it reaches its zenith in the sky. This allows astrophotographers and observers to view this amazing nebula high in the sky with minimal effects of turbulence in the air and localized light pollution.

Photographing the Soul Nebula

The Soul Nebula is one of the easier celestial objects to capture during fall because of its high apparent magnitude and size. To begin with, you should have a telescope with a focal length of at least 250mm, a dedicated CCD camera or DSLR, and a tracking mount. Next, with your tracking mount, slew your setup to the coordinates of Westerhout 5 and keep plate-solving until you have the target centered in your frame of view. Now, test different exposures and see which is best for your setup. I can capture some of the complex filaments within Westerhout 5 with just a 1-minute exposure shot, but I choose to go with a 5-minute exposure shot as it brings out more of the nebula that is hidden with shorter exposures. 

To get the best results for this target, I suggest getting yourself SHO narrowband filters and a broadband filter. With these filters, you can capture two data sets contributing to your final photo differently. With the narrowband data, you can capture the immense detail in the nebula's composition of Oxygen-III, Hydrogen-alpha, and Sulfur-II gasses without any unnecessary wavelengths from light pollution that could hide these structures. With the broadband data, you can capture more stars surrounding Westerhout 5, the true color of these stars, and the detailed nebulosity hidden with the narrowband filter. Combining these two data sets in post-processing can give you a more detailed photo of Westerhout 5. Below you can see the difference between broadband data and narrowband data.

Once you have everything down, you can start your session plan for the night and capture hours of data of this nebula. However, as is the case with all deep-sky astrophotography targets, the key to a successful image of the Soul Nebula is an adequate amount of integration time for a healthy signal-to-noise ratio. We do this by capturing the four main calibration frames (light, dark, flat, and bias) and stacking them 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.

I was able to capture the photo of the Soul Nebula below using a one-shot CCD Camera (ZWO ASI294MC Pro), a dual-narrowband filter (Optolong L-Extreme) for the nebula, a broadband filter (Optolong L-Pro) for the true star colors, and a refractor telescope (100mm Aperture, 900mm focal length) with guiding. To check out my equipment in more detail, click here. Using a duel-narrowband filter, I extracted the Oxygen III and Hydrogen Alpha gasses from the nebula's composition. I'll publish an article soon on how to do this yourself!

Soul Nebula Details:

• IC 1848

• Object Type: Emission Nebula

• Constellation: Cassiopeia

• Distance: 6,500 light-years

• Apparent Magnitude: +6.5

• Apparent Size: 150 x 75 Arc Minutes

Resources:

W5 - The Soul Nebula (NASA)

The Truth About Hubble, JWST, and False Color (NASA)

Constellation Guide - Westerhout 5

Gallery of Soul Nebula