NGC 891 comfortably takes its place within the pantheon of these particular edge-on galaxies such because the Sombrero (Messier 104) in Virgo and NGC 4565 in Coma Berenices. It’s arguably the best inclined spiral seen within the autumn sky. This showpiece object has a SA(s)b classification (see under), however its virtually totally edge-on presentation makes a definitive designation problematic. Astronomers consider it bears some resemblance to our personal Milky Manner galaxy.
NGC 891 is situated 3.5 levels east of magnitude +2.1 Almach (gamma [γ] Andromedae), the gorgeous double star. It additionally lies 3.5 levels west of M34, the great open cluster mendacity throughout the border in Perseus. NGC 891 has the benefit of by no means setting (circumpolar) in UK skies. In late November it culminates excessive overhead (altitude of over 76°) at about 10.30pm GMT.
NGC 891 is a really enticing proposition for beginner imagers, with deep pictures simply capturing the distinguished obscuring lane of mud and interstellar fuel that runs alongside the whole thing of its 13.5 arcminute-long main axis. In contrast to the aforementioned NGC 4565, no distinguished bulge is current. Though shining at a comparatively brilliant magnitude +10, on a clear and moonless evening you’ll in all probability want a four-inch telescope to identify it as a needle-like slither of sunshine and the drastically elevated mild grasp and determination of a 300mm (12-inch) ‘scope to glimpse the mud lane.
The galaxy can also be peppered with many foreground stars, which provides to its visible attract. A shocking sight from a darkish nation sky, NGC 891 is a sight to behold!
Galaxy cluster ACO 347
If you happen to’re observing by way of a big telescope or wide-field imaging, then you definitely would possibly come throughout a gathering of faint smudges of sunshine underneath a level east of NGC 891. That is Abell 347 (ACO 347), a part of the the Perseus–Pisces Supercluster, an enormous filament of galaxy clusters that’s maybe the obvious supercluster within the sky, which isn’t stunning contemplating its large wall of galaxies extends virtually 300 million mild years throughout the cosmos.
It’s thought to lie 250 million mild years away and, regardless of its huge distance it nonetheless covers 60 levels of sky, from the Perseus cluster (Abell 426) at its excessive jap finish, by way of Abell 347 and 262 in Andromeda and the NGC 507 and NGC 383 galaxy teams in northern Pisces, and at last to some smaller and extra obscure galaxy teams on the western finish, such because the NGC 7515 group just under the Nice Sq. of Pegasus.
Abell 347 is difficult to look at with something lower than a 300mm (12-inch) telescope. It’s not a wealthy cluster by any means, thought to comprise at most 50 galaxies mendacity 240 million mild years away. Giant beginner telescopes and pictures reveal seven NGC galaxies, 4 brighter than fourteenth-magnitude inside a 20 arcminute discipline, with round a dozen general overlaying a level.
The brightest galaxy in ACO 347 is thirteenth-magnitude NGC 910, a common-all-garden spherical elliptical with a brilliant core that spans some 2 x 2 arcminutes throughout. This ought to be seen in a 300–350mm (12- to 14-inch) telescope from our shores. NGC 911 and NGC 909 are barely fainter and smaller ellipticals, with NGC 906 being a more durable prospect as a face-on, barred spiral (class SBab).
Galaxy morphological classification system
The Hubble morphological classification system was decided in 1926 by the good American astronomer Edwin Hubble, who broadly divided galaxies into spirals (S), ellipticals (E), lenticulars (S0) and irregulars (Irr), additional classifying spirals in accordance with the tightness of the spiral arm construction and diploma of a central bulge, and whether or not a central bar is current. The extra tightly wound specimens with a pronounced bulge have been classed Sa, progressing by way of Sb and Sc because the arms develop into extra open with an ever-smaller bulge (equal barred spirals are denoted as SBa to SBc).
Gérard Henri de Vaucouleurs, the good twentieth-century French astronomer, devised an extension to the Hubble system, first described in 1959. Merely, it retains the 4 primary Hubble courses however divided galaxies on the presence or lack of a central bar; class SA for no bar, with SB for a barred spiral and SAB for an intermediate class denoting the presence of a weak bar.
He additionally added additional divisions and knowledge for spiral arms and ring-like construction (r (ring current), s (no ring) and rs (transitional).
Ellipticals, featureless-looking galaxies the place star formation has lengthy ceased, are classed in accordance with their diploma of flatness; E0, being essentially the most spherical examples, by way of to E7, cigar-shaped specimens. Lenticulars are an intermediate class between elliptical and spiral galaxies, exhibiting a distinguished bulge surrounded by a featureless disc. Usually, there’s little on-going star formation.
