The Night I Met the Crab Pulsar

We all have goals as observers. A beginner anticipates his or her first glimpse of Jupiter's Great Red Spot or Saturn's rings. More experienced amateurs seek out faint planetary nebulae, extragalactic supernovae, and small-scale lunar features like domes and rills. I've had many goals as an observer, including ones I first thought impossible. But I've held onto them hoping that one day the opportunity to use a sufficiently large telescope would present itself.

Somewhere on that list was the Crab Nebula pulsar also known as PSR B0531+21 — the neutron star at the heart of the nebula remaining after the supergiant progenitor exploded in AD 1054. I've lost count how many times I've observed the nebula itself with its eerie, synchrotron glow, dark bays and tantalizing filamentary structure. I knew that hidden from view, a rotating neutron star spinning at 30 times per second generated the lion's share of the energy that illuminates the Crab. How I wanted to see that star! But at magnitude 16.5 and interred within the densest part of the nebula my 15-inch Dob wasn't up to the task. I know — I tried.

Into the beast's lair

My ticket arrived in the wee hours of September 5, 2021, at the Northern Nights Star Fest held by the Minnesota Astronomical Society. Not only was the sky quite dark but atmospheric seeing improved as the hours passed. With the club's 30-inch (76-cm) Dob we enjoyed spectacular views of stellar associations and globular clusters in M31 and M33. Well after midnight, fellow club member Brandon Hamil and I had the giant eye to ourselves so I asked him to direct it toward the Crab.

With an O III filter I could make out several prominent filaments that defined the arthropod’s leggy outline, then looked up a photograph on my phone that I could use to guide me to the central pulsar. Matching stars in the image to field stars I carefully threaded a path to the Crab's core until arriving at the 16th-magnitude star that lies just 5″ northeast of the pulsar. Despite competition from the Crab's cottony core the star was not difficult to see. Spotting the pulsar took a little more teasing.

I increased the magnification to 572× and could quickly tell that the 16th-magnitude star appeared elongated, hinting at the pulsar's presence. I patiently waited for those crystal instants of near-perfect seeing. When they came, I was able to cleanly separate the fainter pulsar from its "companion." My first neutron star!

Like so many observational challenges over the years it was a mere blip of light. Oh, but what a blip. To behold the exotic remnant of a star that had all but obliterated itself nearly a thousand years ago brought a quiet joy. No words — just a feeling of connection to the bygone souls who must have been equally taken aback by what they saw.

To my knowledge the Crab is the only pulsar within the visual range of amateur telescopes. While I used a 30-inch telescope for my observation, Contributing Editor Howard Banich spotted it “with difficulty” in his 20-inch Dob. If you can get a hold of it, Banich wrote an in-depth report of his sighting with a much larger instrument in the February 2019 issue of Sky & Telescope. Stop by Howard's Nebulae webpage to read more on his observations and work.

At just 20 kilometers (12 miles) across the Crab pulsar is smaller than the Martian moon Phobos yet so dense a sugar cube's worth would weigh around a billion tons. The object spins at the dizzying rate of 30 times per second. Converted to sound its steady pulse reminds me of the sound my snowblower engine makes when chomping through heavy snow. The nebula proper is currently 11 light-years across and continues to expand at the rate of about 1,500 kilometers per second, or 0.15ʺ per year. During an average U.S. human lifetime of 77 years, that amounts to 11.6ʺ or 3ʺ less than the apparent diameter of Mars at its January 2025 opposition. The neutron star and cloud of glowing debris are all that’s left of the original supergiant which exploded as a Type II supernova.

Detonation!

Chinese, Japanese, and Arabic sources recorded the appearance of the Crab supernova in Taurus on the morning of July 4, 1054. Rivaling Venus in brilliance it remained in view for nearly two years. More than seven centuries later in 1731 English astronomer John Bevis discovered a nebula at the location. French comet hunter Charles Messier independently recovered it while searching for Halley's Comet at its first predicted return in 1758. What would later be called the Crab Nebula inspired the creation of his catalog of 110 deep-sky objects and became its first entry — M1.

In 1987 my wife and I visited Chaco Culture National Historic Park in New Mexico. Visitors to the park can hike down an east-facing cliff, look up at a horizontal overhang and see a striking pictograph of a lunar crescent, star symbol, and hand. It was at the top of my must-see list. While definitive proof is lacking, the figures may represent an Anasazi artist’s record of the conjunction of the waning crescent with the supernova at dawn in 1054. I stood beneath the overhang, faced the cloudless, blue sky and imagined the long-ago scene.

My adventures with the Crab encapsulate what I love most about astronomy — we get to be kids for life, staying up late exploring new places and traveling across time.

See a supernova tonight!

While seeing a bright Milky Way supernova is uncommon, the extragalactic variety are frequent because galaxies are so abundant. Several become bright enough every year to see in an 8-inch telescope (see my Going Deep column in the February 2023 issue of Sky & Telescope, page 57). There's a beauty visible right now in the 10th-magnitude spiral galaxy NGC 4216 in the Virgo Cluster. Japanese amateur Koichi Itagaki discovered supernova SN 2024gy on January 4th at magnitude 16.3, but it has since brightened to 12.8 (Jan. 18). Located in northern Virgo about 6.5° southeast of Denebola in Leo, SN 2024gy ascends high enough by local midnight to make it an easy catch. (Update: After a long spell of clouds I saw it for myself on Jan. 18.4 UT. at 145x in my 15-inch reflector. Very impressive how brightly and unmistakably the supernova beams from the galaxy's gossamer disk. A must-see.) Here's a finder map.

Happy trails!