Galaxies · Constellation Ursa Major

Surfboard Galaxy (Messier 108 / NGC 3556)

J2000 coordinates, Tully-Fisher distance (45.9 Mly), magnitude 10.00, mottled edge-on disk, H I supershells, and observing guide for Messier 108.

Right Ascension (J2000.0)11h 11m 31.00s
Declination (J2000.0)+55° 40′ 26.8″
Primary ClassificationNearly edge-on barred SB(s)cd spiral galaxy in Ursa Major
Best Observing SeasonLate Winter to Spring (February–June)

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.

Astrometric, Photometric, and Physical Parameters for Surfboard Galaxy (Messier 108 / NGC 3556)
ParameterValueUncertaintyMethod & EpochQuality StatusSource Archive
Integrated visual magnitude (V)10 mag± 0.1 magIntegrated CCD aperture photometrydefinitiveRevised New General Catalogue and Index Catalogue (RNGC/IC)
Distance in light-years45900000 ly± 3600000 lyMulti-band infrared Tully-Fisher relation (14.1 ± 1.1 Mpc)high-confidenceSIMBAD Astronomical Database (CDS)
Apparent major axis8.7 arcmin± 0.4 arcminOptical 25 mag/arcsec² isophotal dimensions (8.7′ × 2.2′)definitiveRevised New General Catalogue and Index Catalogue (RNGC/IC)
Heliocentric recession velocity699 km/s± 2 km/sH I 21-cm synthesis rotation velocitydefinitiveSIMBAD Astronomical Database (CDS)
Measurement Uncertainties & Competing Solutions: Because M108's 75° inclination and chaotic internal dust lanes complicate Cepheid/TRGB photometry, infrared Tully-Fisher relations provide its primary distance of 14.1 ± 1.1 Mpc (45.9 ± 3.6 Mly).

J2000 Equatorial Sky Chart & Culmination Altitude

The chart below plots Surfboard Galaxy (Messier 108 / NGC 3556) at RA 11h 11m 31.00s, Dec +55° 40′ 26.8″ within Ursa Major, 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.

J2000 Equatorial Sky Position (Ursa Major) +90° 0° −90° 24h 12h RA 0h Peak Meridian Altitude 74° 40°N Lat 4° 30°S Lat RA: 11h 11m 31.00s Dec: +55° 40′ 26.8″ Epoch: J2000.0 · V = 10 mag First-party vector diagram derived from IAU / CDS SIMBAD / Gaia DR3 astrometry.

Astrophysical Context & Structure

Discovered by Pierre Méchain on February 19, 1781, and added to the Messier catalog by Owen Gingerich in 1953 from Messier's handwritten manuscript notes, Messier 108 (NGC 3556, the Surfboard Galaxy) is an isolated, loosely wound SB(s)cd barred spiral galaxy lying 45.9 million light-years away in Ursa Major. Viewed at a 75-degree inclination (just 15 degrees from edge-on), M108 stretches ~110,000 light-years across and completely lacks a prominent central stellar bulge.

Instead of a clean equatorial dust lane like the Sombrero or Needle galaxies, M108's disk is a chaotic tapestry of dark dust filaments, bright H II star-forming knots, and young blue star clusters surrounding a 24-million-solar-mass central black hole. Very Large Array 21-centimeter radio synthesis maps and Chandra X-ray observations reveal dozens of enormous expanding neutral-hydrogen supershells ('H I chimneys') blown up to several thousand light-years above the galactic plane by correlated supernova explosions, including the bright Type II supernova SN 1969B.

On the celestial sphere, M108 is famous for its cosmic juxtaposition just 48 arcminutes northwest of the Owl Nebula (Messier 97, a Milky Way planetary nebula only ~2,000 light-years away)—placing an extragalactic spiral and a foreground dying star in the same low-power telescope field despite a 23,000-to-1 ratio in true distance.

Practical Visual Observing Guide

Minimum Instrument80–100 mm telescope
Recommended Magnification40×–60× with M97; 120×–180× for mottled disk detail
Best Evening SeasonLate Winter to Spring (February–June)
  • Located 1.5° southeast of Merak (β Ursae Majoris, the lower-right pointer star of the Big Dipper's bowl) and 48′ northwest of the Owl Nebula (M97).
  • A wide-field eyepiece (30×–50×) frames both the elongated 8.7′ × 2.2′ slash of M108 and the round ghostly disk of the Owl Nebula in one unforgettable view.
  • In a 200–300 mm telescope at 120×–180×, a 12th-magnitude foreground Milky Way star sits right near the center of M108, mimicking a bright galactic nucleus amid the mottled dust patches.

Catalog Cross-Identifications & Aliases

Common Aliases: M108 · NGC 3556 · UGC 6225 · Surfboard Galaxy

Cross-Catalog Identifiers for Surfboard Galaxy (Messier 108 / NGC 3556)
Catalog AuthorityIdentifier
MESSIERM 108
NGCNGC 3556
SIMBADM 108
WIKIDATAQ14364
Related Object · Ursa Major

Vacuum Cleaner Galaxy (M109 / NGC 3992)

J2000 coordinates, Tully-Fisher distance (67.2 Mly), magnitude 9.80, grand SB(rs)bc barred spiral, Phecda glare tips, and observing guide for M109.

Related Object · Ursa Major

Bode's Galaxy (Messier 81 / NGC 3031)

Coordinates, Cepheid/TRGB distance (3.63 Mpc / 11.8 Mly), magnitude 6.94, M81–M82 tidal pair, and observing guide for Bode's Galaxy in Ursa Major.

Reference Guide

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

  • Revised New General Catalogue and Index Catalogue (RNGC/IC) (2024/2026 edition): Steinicke, W. 2010, Observing and Cataloguing Nebulae and Star Clusters (Cambridge Univ. Press); Verga, M. OpenNGC (CC-BY-SA 4.0 / data tables) — Wolfgang Steinicke / OpenNGC
  • 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