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This month we wheel through the south­ern lim­its of Auriga, the Char­i­o­teer

Sky at Night Magazine - - DECEMBER -

Tick the box when you’ve seen each one

1 M37

The mis­shapen pen­tag­o­nal form of Auriga, the Char­i­o­teer, plays host to some ex­cel­lent deep-sky ob­jects, the most fa­mous be­ing three open clus­ters of the Messier cat­a­logue, all of which are found in the con­stel­la­tion’s south­ern re­gion. Mag. +5.6 M37 is our first tar­get; it can be found al­most 5º south and frac­tion­ally west of mag. +2.7 Theta (e) Auri­gae. It’s a rich open clus­ter and a great tar­get for smaller in­stru­ments. Use a low power and then grad­u­ally in­crease the mag­ni­fi­ca­tion un­til you get to the most pleas­ing view. The clus­ter con­tains around 150 stars down to 12th mag­ni­tude, grouped into a re­gion ap­prox­i­mately 20 ar­cmin­utes across. A red 9th-mag­ni­tude star shines out from the cen­tre. This clus­ter is 4,400 lightyears from Earth. SEEN IT

2 M36

M36, the Pin­wheel Clus­ter, is 3.75º west-north­west of M37. Vis­ually it is less im­pres­sive than M37, hav­ing fewer mem­bers and – oc­cu­py­ing an area ap­prox­i­mately 12 ar­cmin­utes across – be­ing roughly half its size. De­spite this it’s still a lovely sight through a small in­stru­ment, with a 6-inch scope bring­ing ap­prox­i­mately 60 stars into view. A good num­ber of these are blue-white in colour and bright, at around the mag. +9.0 mark. Out­ly­ing stars ap­pear to cre­ate an al­most cru­ci­form shape, with the in­ter­sec­tion of the cross fall­ing at the clus­ter’s core. M36 is 4,100 lightyears and shines at mag. +6.3, just be­low the thresh­old of naked-eye vis­i­bil­ity. SEEN IT

3 M38

At mag. +7.4, M38 is fainter than its two Messier sta­ble­mates, but its 21-ar­cminute ap­par­ent di­am­e­ter is com­pa­ra­ble with that of M37. The clus­ter is 2.3º north­west of M36 and ap­pears quite loose. It has a very ir­reg­u­lar out­line and is heav­ily pep­pered with 10th- and 11th-mag­ni­tude mem­ber stars. Look out for the fainter and smaller open clus­ter NGC 1907, just 0.5º to the south of M38. It has a mag­ni­tude of +8.2 and ap­pears 6 ar­cmin­utes across, ap­prox­i­mately one-third the size of its larger neigh­bour. NGC 1907 is 4,500 lightyears away and is es­ti­mated to be 500 mil­lion years old. In com­par­i­son, M38 is a young­ster, be­ing 200 mil­lion years old and ly­ing 4,200 lightyears away. SEEN IT

4 NGC 1931

Mag. +11.7 NGC 1931 is lo­cated ap­prox­i­mately 1º west of M36. This is a clus­ter with a sur­round­ing ne­bula made up of re­flec­tion and emis­sion com­po­nents. The pres­ence of tightly packed stars at the heart of the emis­sion sec­tion have drawn par­al­lels with the Trapez­ium Clus­ter at the heart of M42, and NGC 1931 is some­times de­scribed as a minia­ture Orion Ne­bula. The ne­bula stretches to 3 ar­cmin­utes, al­though most views show it to be elon­gated and roughly half this size. A large patch of dif­fuse neb­u­los­ity known as IC 417 sits 42 ar­cmin­utes to the west. In long-ex­po­sure im­ages they are col­lec­tively termed the ‘Spi­der and the Fly’, NGC 1931 be­ing the fly. SEEN IT

5 IC 405

IC 405, the Flam­ing Star Ne­bula, is a pop­u­lar tar­get for astro im­agers, but a tricky ob­ject to glimpse vis­ually. It is 3.1º to the west of NGC 1931 and sur­rounds 6th-mag­ni­tude AE Auri­gae, a run­away star ejected from the Trapez­ium Clus­ter in M42 some two mil­lion years ago. AE Auri­gae isn’t associated with the ne­bula, but pass­ing through it at high speed. As it does this a bow shock from the in­ter­ac­tion pro­duces the en­ergy re­quired to make the ne­bula glow. A trans­par­ent night is re­quired to see any­thing of IC 405. Use a low power eyepiece and, with prop­erly dark-adapted eyes, the Flam­ing Star Ne­bula should ap­pear as a weak, curv­ing glow. SEEN IT

6 .2+287(.

Ko­houtek 2-1 is a mag. +13.8 plan­e­tary ne­bula close to the bor­der of Auriga and Tau­rus. Imag­ine a line be­tween mag. +1.7 El­nath (Beta (`) Tauri) and mag. +2.7 Has­saleh (Iota (f) Auri­gae). Look south­west of the line’s mid­point to find two stars of around mag. +6.6, then ex­tend the line be­tween them west. You will reach a pair of 9th­mag­ni­tude stars; the plan­e­tary ne­bula is 3 ar­cmin­utes north­east of the north­ern star. Un­usu­ally, a low power works bet­ter than a high power here. An OIII fil­ter will also help. The ne­bula has a di­am­e­ter of 2.2 ar­cmin­utes and should ap­pear as a cir­cu­lar glow. Sec­tions of its edge ap­pear brighter, giv­ing the over­all ap­pear­ance of a pair of brack­ets en­clos­ing the in­ner glow. SEEN IT

The Flam­ing Heart Ne­bula, IC 405, is lit by the bow shock of a run­away star speed­ing through it

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