BBC Sky at Night Magazine

Deep-sky tour

We follow the trail of Comet C/2017 T2 PanSTARRS past galaxies great and small


1 M81

Comet C/2017 T2 PanSTARRS passes close to M81 and M82, so our Deep-Sky Tour is geared to this area of sky. Locate them by extending a diagonal across the pan of the Saucepan from Phecda (Gamma (g) Ursae Majoris) through Dubhe (Alpha (a) Ursae Majoris) for the same distance again. M81 and M82 are 2˚ to the north of the point you reach. Bode’s Galaxy, M81, is a bright spiral galaxy. It shines at mag. +7.8 and appears as a 20x11 arcminute glowing oval. The core is bright, showing good condensati­on, but the outer spiral arms need larger apertures to see convincing­ly as they are thin and spindly. M81 is located 12 million lightyears away.  SEEN IT

2 M82

Despite being dimmer than M81, 9th magnitude M82 is easy to find because it lies 37 arcminutes to the north of M81. M82 is known as the Cigar Galaxy because of its distinctiv­e shape. Being so close to M81, it’s easy to get both objects into the same low-power field of view. When you do, the contrast in shape is quite stunning. M82 is an irregular galaxy with high star-formation activity and a prototype for a class of starburst galaxies. Smaller apertures reveal a view which looks like a regular sideways-on spiral. With larger apertures, the core begins to show a mottled appearance with bright knots separated by darker dust lanes. M82 is a member of the M81 group and shares its neighbour’s distance of 12 million lightyears.  SEEN IT

3 NGC 3077

Our next target is NGC 3077, a disturbed elliptical galaxy which is also a member of the M81 group. Again, this galaxy is easy to locate as it’s in the same field as M81 and M82, marking the eastern vertex of a right-angled triangle formed with M81 and M82, M81 sitting at the right angle. NGC 3077 appears as a circular glow through a 150mm scope, much smaller than M81 or M82, with an apparent diameter around 1.5 arcminutes. A similar, albeit slightly larger appearance greets a 250mm scope. Even larger apertures will begin to show a weak, larger glow about 4 arcminutes across which surrounds the 2-arcminute central condensati­on and wide core.  SEEN IT

4 IC 2574

We move slightly further from the M81 and M82 region for our next target, the dwarf spiral galaxy IC 2574. An outlying member of the M81 and M82 group, IC 2574 will also get a close pass by C/2017 T2 PanSTARRS this month, the comet lying 20 arcminutes from the galaxy’s centre at 01:00 BST (00:00 UT) on 27 May. Also known as Coddington’s Nebula, IC 2574 shines at mag. +10.6 but has a low surface brightness, thanks to its 12x6 arcminute apparent size. A study of the galaxy reveals that 90% of its mass is tied up in dark matter. Locate Coddington’s Nebula 2.9˚ east and half a degree south of M82.  SEEN IT

5 NGC 2976

NGC 2976 is another unusual looking galaxy, located 1.3˚ to the south of M81. Although it’s classed as an unbarred spiral galaxy, mag. +10.8 NGC 2976’s spiral arms are difficult, if not impossible to see. A small scope will show it as a weak glow 3 arcminutes across, but having low surface brightness and no evidence of any definite core. A 300mm scope at 200x shows a glowing ellipse with a mottled, uneven texture. Averted vision will show several brighter patches within the galaxy’s irregular border. These are evident on the northwest side. This object is another member of the M81 group and is 11.6 million lightyears away. It was discovered by William Herschel in 1801.  SEEN IT

6 NGC 2985

Next is NGC 2985, the brightest member of the NGC 2985 group. It shines at mag. +10.4 and is located 3.2˚ north and 28 arcminutes west of M81. A 150mm scope reveals a fuzzy glow about 1 arcminute across. Its nucleus appears stellar through small instrument­s. A mag. +12.5 star sits 1 arcminute from the nucleus on the eastern side. This is a marker because with a 250mm instrument the galaxy’s outer halo, formed from a complex wrapping of tightly wound spiral arms, extends beyond this star to present a halo 2 arcminutes across.  SEEN IT

 ??  ?? ▲ Coddington’s Nebula, IC 2574. A study has revealed that 90% of its mass is tied up in dark matter
▲ Coddington’s Nebula, IC 2574. A study has revealed that 90% of its mass is tied up in dark matter

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