Crab Nebula (M1)

This rare deep-sky object known as Messier 1 is a supernova remnant and pulsar wind nebula in the constellation of Taurus. Scientists speculate that this cosmic explosion occurred in 1054 AD, making this object one of the youngest in the sky. When this supernova occurred, astronomers hypothesized the sky was so bright that it looked like daytime during the night for weeks. In addition to its extraordinary complexity, the strange filaments within this nebula also seem to have less mass than those ejected during the original supernova.

"This large mosaic of the Crab Nebula was assembled from 24 individual exposures captured by Hubble over three months. The colors in this image do not match exactly what we would see with our eyes but yield insight into the composition of this spectacular stellar corpse. The orange filaments are the tattered remains of the star and consist mostly of hydrogen. The blue in the filaments in the outer part of the nebula represents neutral oxygen. Green is singly ionized sulfur, and red indicates doubly ionized oxygen. These elements were expelled during the supernova explosion." 

NASA - August 25, 2021

The Crab's Beating Heart

NASA has been using its Hubble Space Telescope to peer deeper into Messier 1, which revealed the nebula’s "beating heart." This beating heart is not an actual heart but rather a rapidly spinning pulsar at its core which releases bright wisps moving outward at half the speed of light to form an expanding ring. The wisps materialize along magnetic field lines within a gas comprising of immensely energetic particles that are propelled into space by a neutron star that is highly magnetized and rotates rapidly.

This time-lapse movie of Messier 1 was created from a series of 10 Hubble exposures. It reveals wave-like rings expanding outward from the nebula’s pulsar (the bright object just below the center of the image). I have always been fascinated with supernovas, and seeing how far technology has come, like analyzing the pulsar winds from the center of Messier 1, is incredible. I hope that one day we will see an active supernova in our night sky during my lifetime, but if not, I am just as satisfied with what the cosmos offer us now.

Location & Best Time to See it

The Crab Nebula is one of the most renowned supernova remnants in the astrophotography community during winter. To observe it yourself, start by finding one of the brightest stars in the sky, Aldebaran, which should have an orange tint. Once you've found this star, try to locate the farthest star connected to Aldebaran in the constellation Taurus. From there, the general area surrounding this star is where Messier 1 is in the sky. The photo below from Stellarium is a good representation of where to find the Crab Nebula in the night sky.

The Crab 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 December – February when it reaches its zenith in the sky. This allows astrophotographers and observers to view this impressive supernova remnant with minimal effects of turbulence in the air and localized light pollution.

Photographing the Crab Nebula

The Crab Nebula has to be one of my favorite celestial objects to capture during the winter season because of its strange structure and intriguing history. Unfortunately, this object is quite harder to photograph because of its small apparent size. So if you cannot plate-solve your images, you'd be lucky to get a decent image of the Crab Nebula. To begin with, you should have a telescope with a focal length of at least 800mm, a dedicated CCD camera or DSLR, and a tracking mount. Next, with your tracking mount, slew your setup to the coordinates of Messier 1 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. For me, I can capture some of the complex filaments within Messier 1 with just a short 30-second 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. 

Because the Crab Nebula is so small, the atmospheric effects and light pollution get in the way of its complex structures. So one thing I highly suggest doing is getting yourself SHO narrowband filters and a broadband filter. With these filters, you can capture two data sets that contribute to your final photo differently. With the narrowband data, you can capture the immense detail in the nebula's composition of Oxygen-III and Hydrogen-alpha gas without any unnecessary wavelengths that could hide this structure. With the broadband data, you can capture the true color of the stars surrounding Messier 1 and the nebulosity hidden with the narrowband filter. Combining these two data sets in post-processing can give you a more detailed photo of Messier 1. 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 supernova remnant. However, as is the case with all deep-sky astrophotography targets, the key to a successful image of the Crab 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 Messier 1 below using a one-shot CCD Camera (ZWO ASI294MC Pro), a dual-narrowband filter (Optolong L-Extreme), 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!

Crab Nebula Details:

• Messier: 1

• NGC: 1952

• Object Type: Supernova Remnant and Pulsar Wind Nebula

• Constellation: Taurus

• Distance: 6,523 light-years

• Apparent Magnitude: +8.4

• Apparent Size: 7 x 5 Arc Minutes

Resources:

Messier 1 - The Crab Nebula (NASA)

StarCharts - Crab Nebula

Constellation Guide - Messier 1

Gallery of Crab Nebula