M81 and Holmberg IX in Ursa Major

Posted by Rod Pommier
on Tuesday, August 13, 2013

by Rod Pommier

Telescope/Mount: Celestron Compustar C14 with Astrophysics 0.75x focal reducer (f/8.3).

Camera: SBIG STL 11000M with Baader Planetarium L, R, G, and B filters.

Location: Pommier Observatory, Portland, OR, USA. 

Dates: 2013-10-06 through 2013-10-10.

Exposures:L:R:G:B=430:70:70:70=10 hours, 40 minutes total exposure. 

M81 is a class Sb spiral galaxy in Ursa Major. It is roughly equal in size to the Milky Way and lies at a distance of about 11.8 million light-years. It is considered a classic grand design spiral with a large central bulge consisting of old population II yellow stars and two major spiral arms consisting of hot blue population I stars. Yet despite this classic appearance, it exhibits some changes that still hint at a recent disruptive interaction. The chief features hinting at a recent interaction are the aberrant parallel dust lanes cutting across the galactic disk, to the lower left of the galaxy's central nucleus in this image. The responsible interaction likely occurred with it's smaller neighbor, M82, which appears far more disrupted than M81. The dwarf irregular galaxy Holmberg IX, seen to the right of M81, is a satellite of M81, analogous to one of the Milky Way's Magellanic clouds.

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