the Nice Bear’s grand-design spiral galaxy  – Astronomy Now


Messier 81 in Ursa Main is gorgeous spiral galaxy. Picture: NASA, ESA and the Hubble Heritage Group (STScI/AURA).

Early spring’s slogan is ‘convey on the galaxies’, however with so many to select from the place do you have to begin to look? You might do a lot worse than to start with magnificent Messier 81 (NGC 3031) in Ursa Main, sometimes referred to a ‘Bode’s Galaxy’, named for the eighteenth-century German astronomer Johann Elert Bode who found it in 1774. 

Messier 81 is a traditional, grand-design spiral galaxy that, shining with an built-in magnitude of +6.8, is vibrant sufficient for a pair of binoculars to entrap, and might be studied by way of a medium-aperture telescope. Moreover, Messier 81 has the shut firm of Messier 82, an interacting edge-on galaxy that gives a picturesque pairing that’s probably the most wanted in the whole sky.

Messier 81 might be situated in Ursa Main’s far north-western nook, north and west of the well-known Plough asterism.

Messier 81 shouldn’t be an particularly giant galaxy, having a bodily diameter of 92,000 mild years. Nevertheless, it presents observers a really beneficiant obvious diameter of 26’ x 14’, tilted at an indirect angle to our line of sight. This makes it one of many largest galaxies within the sky, owing to its shut proximity to us: cosmologically talking, a mere 12 million mild years away.

Messier 81’s morphological classification (Hubble/de Vaucouleurs) is SA(s)ab, indicating that no central bar is current and that its spiral arms aren’t that tightly wound. Deep photographs, together with many very good examples shot by novice astronomers, present M81 as stunning and sleek, consisting of fairly a big central area dominated by older stars, which give it a tell-tale yellow forged. Properly seen too are its two bluish, well-defined however skinny spiral arms, that are dotted with quite a few pinky-red H-II areas and host over 100 star clusters, residence to many younger, scorching stars which have fashioned prior to now few million years.

Messier 81 offers its identify to the M81 Group, a gathering of over 30 galaxies, together with M82, which kind the closest galaxy group to our Native Group.

Messier 81 and 82 are strongly interacting and astronomers imagine that each hundred million years or so M81 makes a run at M82. Messier 81 is far the extra huge of the pair, ten-times extra astronomer’s assume, and causes harmful havoc by triggering robust episodes of star formation in M82. The bigger galaxy doesn’t come away unscathed from these encounters although, as there’s potential proof for accelerated star formation in M81 following a coming collectively some 300 million years in the past. Its japanese spiral arm has been deformed by an encounter solely 10 million years in the past.

M81 and M82 side-by-side. Picture: Patrick Gilliland.

Messier 81 is an observational gem, but it surely’s a little bit tough to search out. From Phecda (gamma [γ] Ursae Majoris [UMa]) and Dubhe (alpha [α] UMa), two of the Plough’s ‘pan’ stars, think about a diagonal line drawn between these two stars and prolong it the identical distance once more away from Dubhe; you must land near M81. In early March, M81 culminates at about 11pm GMT on the dizzy peak of 72 levels altitude, inserting it advantageously excessive overhead. In actual fact, M81 by no means units from UK shores (is circumpolar), so it may be noticed for lengthy intervals.

Below good circumstances on a moonless night time, a telescope within the 80–100mm (~three- to four-inch) class working at low powers will reveal the galaxy central core engulfed in an oval-shaped haze some 15’ x 7’ in obvious diameter. Its low floor brightness, an affliction widespread to the vast majority of galaxies, could make M81 powerful to identify in a suburban sky or in hazy circumstances. Close by M82 might be seen as pencil-shaped, providing a really condensed core at excessive energy. You’ll have to improve to the sunshine grasp of maybe a 400mm (16-inch) telescope, working at low energy, to catch a glimpse of M81’s easy and refined spiral arms.

Imagers ought to fastidiously scrutinise their work in case M81 (or M82 for that matter) produces a shocking supernova. Almost 30 years in the past, Messier 81 was the centre of consideration owing to the sudden look of supernova 1993J, a type-IIb supernova that peaked at magnitude +10.5 and thrilled astronomers throughout the globe.

Photos present M81 with a yellowish central area, dominated by outdated stars, and two bluish, sweeping and well-defined spiral arms dotted by quite a few pinky-red HII areas, websites of ongoing star formation of younger scorching stars.

Messier 82 seen as a composite of Chandra, HST (Hubble) and Spitzer photographs. X-ray information recorded by Chandra seems in blue; infrared mild recorded by Spitzer seems in purple; Hubble’s observations of hydrogen emission seem in orange, and the bluest seen mild seems in yellow-green. Picture: NASA/JPL-Caltech/STScI/CXC/UofA/ESA/AURA/JHU.

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