Image Centered on Ra. 09 : 55.6 (h:m) Dec.+69 : 04 (deg:m) Distance 12 million light years
Spiral Galaxy M81 (NGC 3031),
type Sb, in Ursa Major
Bode's Galaxy
Information (From the SEDS website )
Discovered by Johann Elert
Bode in 1774.
M81 is one of the easiest and most rewarding galaxies to observe for the amateur
astronomer on the northern hemisphere, because with its total visual brightness
of about 6.8 magnitudes it can be found with small instruments. Brian Skiff of
Lowell Observatory reports that he could see M81 with the unaided naked eye
under exceptionally good viewing conditions (i.e., clear dark skies), and is at
least the fourth observer who reported to have done so !
The pronounced grand-design spiral galaxy M81 forms a most conspicuous physical
pair with its neighbor, M82, and is the brightest and probably dominant galaxy
of a nearby group called M81 group. A few tens of million years ago, which is
semi-recently on the cosmic time scale, a close encounter occurred between the
galaxies M81 and M82. During this event, larger and more massive M81 has
dramatically deformed M82 by gravitational interaction. The encounter has also
left traces in the spiral pattern of the brighter and larger galaxy M81, first
making it overall more pronounced, and second in the form of the dark linear
feature in the lower left of the nuclear region. The galaxies are still close
together, their centers separated by a linear distance of only about 150,000
light years.
M81 is the first of the four objects originally discovered by Johann Elert Bode,
who found it, together with its neighbor M82, on December 31, 1774. Bode
described it as a "nebulous patch", about 0.75 deg away from M82, which "appears
mostly round and has a dense nucleus in the middle," and included it as No. 17
in his list. Pierre Méchain independently rediscovered both galaxies as nebulous
patches in August 1779 and reported them to Charles Messier, who added them to
his catalog after his position measurement on February 9, 1781.
Using the Hubble Space Telescope, a team under Wendy Freedman of the Carnegie
Institution of Washington has investigated 32 Cepheid variables in M81 and
determined the distance to be 11.0 million light years, in 1993 well before the
HST was refurbished. Together with the new distance scale correction implied by
the results of ESA's Hipparcos satellite, the true distance of M81 is probably
closer to 12.0 million light years. See the H0 Key Project Team's work on M81
(paper 1 and 2, 1994).
On Sunday, March 28, 1993, a type II supernova (1993J) occured in M81, which was
discovered by the Spanish amateur astronomer Francisco Garcia Diaz from Lugo
(Spain), and reached a brightness of about mag 10.5 in its maximum. The remnant
of this supernova was imaged in the radio light at 3.6 cm wavelength from
roughly six to 18 months after the explosion, with a global Very Long Baseline
Interferometer (VLBI) array of radio telescopes in Europe and North America.
Investigations performed in 1994 have indicated that M81 has probably only
little dark matter, as its rotation curve was found to fall off in the outer
regions; this is in contrast to many galaxies, including our own Milky Way, for
which the rotation curve increases outward. To explain the velocity of the stars
in these regions, the galaxy must have a certain amount of mass. However, the
total mass observed in luminous matter - stars and nebulae - is typically
insufficient to explain this behaviour; thus it is assumed that there is a
significant portion of mass in galaxies is non-luminous, dark matter (or at
least low-luminosity matter). For M81, the percentage of dark matter is now
estimated to be lower than average.
In 1995, Perelmuter and Racine investigated the region around M81 for globular
clusters, and found about 70 candidate objects for the globular cluster system
of M81 (Perelmuter and Racine, 1995). They estimate the total population at 210
+/- 30 globulars.
In December 1990, the ASTRO-1 Space Shuttle mission (STS-35) transported
telescopes into the Earth's orbit, including the UIT (Ultraviolet Imaging
Telescope) which obtained images of M81 (in the ultraviolet light; these were
compared with the visible light image, and combined to an interesting and
informative overlay; an animation [433 k MPG] showing a morphing from the UV to
visual image of M81 is available). Previously, M81's UV radiation had been
investigated by the Soviet Astron orbital observatory. Bill Keel has assembled a
series of images of M81 in the different parts of the electromagnetic spectrum
from the radio part to the X-rays region.
Optics and Exposure Data
Telescope, Vixen R200ss 8 inch Newtonian at F4 (Fl 800mm) with a Televue Coma Corrector and aftermarket Moonlite accessories focuser.
Mount, Losmandy G11 with Gemini control electronics
Imager, Starlite-Xpress SXV-h9 using Schuler Ha and OIII Optical filters
Exposure data, Luminance =120 minutes Ha = 90 minutes RGB 60 minutes each channel. Ha and red combined to create red channel
Images acquired with Astroart and aligned then combined in Maxim Dl. Final RGB composite processed with Photoshop Cs
Images acquired from my backyard - " Dirt Clod Observatory" in Antelope California
