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Messier 81 and 82 interacting galaxies in Ursa Major [Explored] | by john.purvis
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Messier 81 and 82 interacting galaxies in Ursa Major [Explored]

Its been a couple of years since Ive imaged this pair.


Tried 10 minute exposures this time which seemed to work well. Stars were a bit more bloated with the longer exposures but used Morphological Transform in PixInsight to good effect.


Ursa Major is always visible from my location so will try to accumulate more subs come the autumn/winter - at 55N, DSO imaging is almost over until late August.


M81 is a large spiral galaxy in Ursa Major that is reasonably local to us at 12 million light years. Its companion, M82 has been disrupted by an encounter with M81 in the past.


M82 is a starburst galaxy with intense star formation triggered by the gravitational influence of M81. The red fan-like filaments at right angles to the axis of the galaxy are formed by a "superwind". The intense star formation has resulted in multiple supernovae explosions occurring about once every 10 years - the explosions power the super wind. The filaments are expanding outwards at about 600 miles a second and glow brightly in hydrogen alpha (red). They are also a very strong source of radio emission, listed as 3C 231 in the 3rd Cambridge catalogue of radio sources.


A very faint satellite galaxy to M81 - Holmberg IX can just be seen as a faint blue smudge above its parent galaxy.



480/80mm f/6 Altair Starwave triplet refractor.

Altair Planostar 1.0 x FF with 2 inch IDAS LPS D1 filter

Astro-modified Canon 80D at ISO400; 9 x 10 minute subs + 1 x 5 minute test sub (95 mins total integration).

NEQ6 Pro Mount with Rowan modified belt drives. 2-star align.

Laptop with BackyardEOS for focusing and acquisition.



60 dark frames - sensor temperature matched from Dark Library (10-11c)

80 bias frames

60 flat frames (Electroluminescent panel @ 1/40s)


QHY Polemaster alignment -

Error measured by PHD2= 0.6 arc minute.

RA drift +0.28 arcsec/min

Dec drift -0.14 arcsec/min



PHD2 guiding with ZWO ASI290mm/Altair lightwave 209/50mm secondary scope. Alternate subs dithered.

RA RMS error 0.47 arcsec, peak error -2.35 arcsec

Dec RMS error 0.41 arcsec, peak error -2.74 arcsec



Center (RA, hms):09h 55m 39.082s

Center (Dec, dms): +69° 20' 28.639"

Size:71.2 x 51.8 arcmin

Pixel scale:1.59 arcsec/pixel


Light Pollution-

SQM (L) at middle of session (2350 hrs UT) 20.1 mag/arcsec2 .

Typical of outer suburbs - Bortle scale = 5/9 Yellow



Temp =5.8c

Humidity = 66%

Dew point = 0c

Occasional very light cloud, no subs lost to cloud.


Post processed in PixInsight 1.8.

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Taken on April 14, 2020