Crab Pulsar (PSR B0531+21 / NP 0532)
Coordinates, 33.08 ms spin period, 16.5-mag optical flashes, spin-down luminosity, and high-aperture observing guide for the Crab Pulsar.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Time-averaged optical visual magnitude (V) | 16.5 mag | ± 0.1 mag | High-speed optical stroboscopic photometry (flashes 30.2 times per second) | definitive | SIMBAD Astronomical Database (CDS) |
| Rotational spin period (33.08 ms expressed in days) | 3.829e-7 d | exact (defined) | Radio & optical pulse timing (P = 0.033085 s, slowing by 36.4 ns/day) | definitive | SIMBAD Astronomical Database (CDS) |
| Canonical neutron star mass | 1.4 M☉ | 1.3 to 1.8 M☉ | Core-collapse neutron star equation-of-state & spin-down moment of inertia | model-dependent | SIMBAD Astronomical Database (CDS) |
| Rotational spin-down power | 120000 L☉ | ± 15000 L☉ | Magnetic dipole braking power dE/dt ≈ 4.6 × 10^38 erg/s | high-confidence | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Crab Pulsar (PSR B0531+21 Neutron Star) at RA 05h 34m 31.97s, Dec +22° 00′ 52.2″ within Taurus, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
The Crab Pulsar (PSR B0531+21, variable-star designation CM Tauri) is the 972-year-old magnetized neutron star spinning at the center of the Crab Nebula (Messier 1) in Taurus, left behind by the core collapse of SN 1054. Discovered at radio wavelengths in late 1968 using the 300-foot Green Bank telescope and optically identified in January 1969 by Cocke, Disney, and Taylor at Steward Observatory as the southwestern star of the central 16th-magnitude double in Baade's photographs, the Crab Pulsar was the first pulsar ever detected in visible light.
Packing roughly 1.4 solar masses of neutron-degenerate matter into a sphere only ~20–24 kilometers in diameter, PSR B0531+21 rotates on its axis once every 33.085 milliseconds (30.22 revolutions per second) with a surface magnetic field of ~3.8 × 10^12 Gauss. That rapid rotation acts as a colossal relativistic dynamo: as the pulsar slows down by 36.4 nanoseconds per day, its rotational kinetic energy Loss (~4.6 × 10^38 erg/s, or 120,000 solar luminosities) powers the entire Crab Nebula's synchrotron glow and drives dynamic polar jets and equatorial wisps imaged by Hubble and the Chandra X-ray Observatory.
Because the pulsar flashes on and off 30.2 times per second (with a main pulse and an interpulse each rotation), human eyes—whose flicker-fusion limit is ~20–25 Hz—perceive it as a steady magnitude 16.5 point of light unless viewed through a synchronized mechanical chopper wheel.
Practical Visual Observing Guide
- For visual observers with large apertures (350–450 mm / 14–18 inches and larger) under dark, steady skies at 250×–350×, the Crab Pulsar is the only neutron star in the universe directly visible to the human eye!
- Look at the center of Messier 1 for a close 4.7-arcsecond pair of 16th-magnitude stars oriented northeast–southwest: the slightly brighter northeastern star (mag 15.8) is a foreground field star, while the southwestern star (mag 16.5) is the Crab Pulsar itself.
Catalog Cross-Identifications & Aliases
Common Aliases: PSR B0531+21 · PSR J0534+2200 · CM Tauri · NP 0532
| Catalog Authority | Identifier |
|---|---|
| SIMBAD | PSR B0531+21 |
| WIKIDATA | Q13651 |
Related Objects, Comparisons & Guides
Crab Nebula (Messier 1 Supernova Remnant)
Coordinates, Gaia DR3 distance (1.96 kpc), SN 1054 history, pulsar wind physics, and observing guide for the Crab Nebula (M1) in Taurus.
Cassiopeia A (3C 461 Young Supernova Remnant)
Coordinates, kinematic distance (3.4 kpc), JWST/Chandra ejecta knots, and high-aperture observing guide for Cassiopeia A (3C 461).
Cygnus X-1 (HDE 226868 X-Ray Black Hole)
Coordinates, VLBA/Gaia distance (2.22 kpc), 21.2-M☉ stellar black hole mass, 5.60-day O-supergiant binary, and observing guide for Cygnus X-1.
Sagittarius A* (Galactic Center Black Hole)
Coordinates, GRAVITY S2 stellar orbit distance (8,277 pc) & mass (4.297 × 10^6 M☉), EHT 51.8 μas shadow, and Galactic Center guide for Sgr A*.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Scientific Sources & Dataset Provenance
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg