Messier 81 – Bode's Galaxy

Key Scientific Data

Object type: Grand-design spiral galaxy – SA(s)ab

Constellation: Ursa Major

Other designations: M81, NGC 3031, UGC 5318, PGC 28630, Bode's Galaxy

Distance from Earth: approximately 11.6 million light-years

Diameter: approximately 90,000 light-years

Apparent size: approximately 27′ × 14′

Apparent magnitude: approximately 6.9

Inclination: approximately 59°

Right Ascension: 09h 55m 33s

Declination: +69° 04′

Discovered by: Johann Elert Bode, 1774

Nucleus: Active galactic nucleus hosting a supermassive black hole of approximately 70 million solar masses

Light-travel time: approximately 11.6 million years

Description

Messier 81 (M81), known as Bode's Galaxy, is a large spiral galaxy approximately 11.6 million light-years away, comparable in size to the Milky Way.

Its prominent yellowish central bulge is dominated by older stellar populations, while two well-defined spiral arms contain younger blue stars, star-forming regions and dark interstellar dust lanes.

At its centre lies a supermassive black hole of approximately 70 million solar masses, considerably more massive than Sagittarius A* in our own Galaxy.

A Classic Grand-Design Spiral

M81 is one of the finest nearby examples of a grand-design spiral galaxy, characterised by two long, continuous and remarkably symmetrical spiral arms.

Its structure has been influenced by gravitational interactions with neighbouring galaxies, particularly M82 and NGC 3077, making it an important system for studying spiral dynamics and galactic evolution.

M81 and M82 – A Gravitational Encounter

M81 belongs to a gravitationally interacting group that includes M82 (the Cigar Galaxy) and NGC 3077.

Close encounters hundreds of millions of years ago redistributed enormous quantities of hydrogen gas, creating tidal structures and stimulating star formation.

The consequences are particularly evident in M82, where an intense starburst is producing new stars and powerful outflows of gas. M81 also preserves evidence of these interactions in its gas distribution and spiral structure.

Curiosities

M81 was discovered by Johann Elert Bode on 31 December 1774 and subsequently included in Charles Messier's catalogue in 1781.

Despite its apparent magnitude of 6.9, its relatively low surface brightness makes naked-eye observation extremely challenging.

Measurements of Cepheid variable stars have helped establish its distance, while SN 1993J, a particularly well-studied supernova, provided valuable insights into the final stages of massive stellar evolution.

Looking Back in Time

The light captured from M81 began its journey approximately 11.6 million years ago, during Earth's late Miocene epoch.

At that time, Earth's climate was becoming progressively cooler and drier, grasslands were expanding, and early horses, elephants and great apes inhabited different regions of the planet.

Humans had not yet appeared, and the evolutionary separation between the human lineage and that of chimpanzees was still several million years in the future. The earliest known hominins would emerge much later, while Homo sapiens would not appear until approximately 300,000 years ago.

Throughout these profound evolutionary changes, the photons recorded in this image travelled across intergalactic space.

This photograph reveals M81 as it appeared millions of years before the emergence of humanity, preserving a distant chapter of cosmic history.

Image Data

Total integration time: 20h 24m 20s

Integration by filter:

  • L-Pro: 4h 58m 40s

  • Red: 5h 25m 20s

  • Green: 5h 18m 20s

  • Blue: 4h 42m

Equipment:

  • Telescope: Artesky ARTEC 250 Pro

  • Camera: ToupTek ATR2600M

  • Mount: 10Micron GM2000 HPS II

  • Filters: Optolong L-Pro, Red, Green, Blue 2"

  • Accessories: Pegasus Astro Prodigy Microfocuser, ToupTek AFW-L 7×2", WandererAstro WandererBox Pro V3

  • Software: Adobe Photoshop, Pleiades Astrophoto PixInsight, Stefan Berg Nighttime Imaging 'N' Astronomy (N.I.N.A. / NINA)

For further information and the full-resolution image, visit AstroBin:

M81 – Bode's Galaxy – AstroBin