'((3 6.< TOUR

We search out the ce­les­tial won­ders amidst the Ea­gle’s tail feath­ers

Sky at Night Magazine - - THE SKY GUIDE -

Tick the box when you’ve seen each one 1 NGC 6751

All of this month’s Deep-Sky Tour ob­jects are lo­cated around the re­gion of sky rep­re­sent­ing the lower body and tail of Aquila, the Ea­gle. The first is plan­e­tary ne­bula NGC 6751, which can be found at the south­ern apex of a squat isosce­les tri­an­gle that uses mag. +3.4 Lambda (h) and mag. +4.0 12 Aquilae as its base. NGC 6751 is around 12th mag­ni­tude, with a cen­tral star shin­ing at mag. +13.9. It can be seen in a 6-inch scope, but its small (10 arc­sec­ond) di­am­e­ter is best re­vealed with larger in­stru­ments. A 10-inch scope at 250x mag­ni­fi­ca­tion shows a cir­cu­lar, ring-like ob­ject with a bright cen­tre that gen­tly fades away to­wards the outer ring. Larger scopes still be­gin to show dark mot­tling, which be­comes es­pe­cially ev­i­dent south of the core. Ĵ SEEN IT

2 NGC 6790

Our next ob­ject is NGC 6790, an­other plan­e­tary lo­cated far­ther up Aquila’s body, close to the cen­tre of a tri­an­gle formed by mag. +3.4 Delta (b), mag. +4.6 Nu (i) and mag. +5.1 23 Aquilae. At mag. +10.7, this ne­bula shouldn’t give much trou­ble for larger in­stru­ments, but it is chal­leng­ingly small at just 7 arc­sec­onds. Its size tends to make it ap­pear quite star-like at low mag­ni­fi­ca­tions, so don’t be afraid to up the power. Like many plan­e­taries, NGC 6790 re­sponds well to the use of UHC or OIII fil­ters. The lat­ter can be used to con­firm you’ve got it via the ‘blink tech­nique’: pass an OIII fil­ter be­tween your eye and eyepiece and the ne­bula should main­tain its bright­ness while the stars dim. Do this sev­eral times and the star-like ne­bula should be­come ob­vi­ous. Ĵ SEEN IT

3 NGC 6760

A much eas­ier nearby ob­ject for smaller scopes is glob­u­lar clus­ter NGC 6760. It an be found 4º south­west of Delta Aquilae and at mag. +8.8 should be easy to lo­cate. Its iden­ti­fi­ca­tion is fur­ther as­sisted by a small as­ter­ism of stars nearby form­ing a squashed pen­tagon, in which NGC 6760 marks the north­ern point. A 6-inch scope shows a 2-ar­cminute di­am­e­ter haze with a mot­tled gran­u­lar­ity. Un­der good con­di­tions, 150x mag­ni­fi­ca­tion should re­solve some of the clus­ter’s stars. In­creased aper­ture de­liv­ers ex­tra de­tail, although even a 10-inch scope doesn’t re­solve ev­ery­thing. This size of scope shows NGC 6750 to be al­most dou­ble the size shown through a 6-inch in­stru­ment. The larger aper­ture also re­veals a slight east-west elon­ga­tion. Ĵ SEEN IT

4 NGC 6741

Plan­e­tary ne­bula NGC 6741, also known as the Phan­tom Streak Ne­bula,

is 2.5º south­west of NGC 6760. This is an 11th-mag­ni­tude ob­ject with an over­all size of 9x7 arc­sec­onds. Once again, given its size, this ob­ject is best suited for larger aper­tures, NGC 6741 ap­pear­ing quite star­like at lower pow­ers. A mag­ni­tude +12.7 star sits just north of the ne­bula’s cen­tre. At pow­ers be­low 300x it’s dif­fi­cult to sep­a­rate the ne­bula and star, es­pe­cially as the dim­mer star is a good match for the sur­face bright­ness of the ne­bula. It is 7,000 lightyears from Earth, and has a dis­tinctly elon­gated and some­what rec­tan­gu­lar ap­pear­ance when pho­tographed with pro­fes­sional tele­scopes. Ĵ SEEN IT

5 NGC 6704

Our last two ob­jects are easy small tele­scope tar­gets. The first is open clus­ter NGC 6704, sit­u­ated ap­prox­i­mately one-quar­ter of the way along the line from Beta (`) Scuti to­wards 12 Aquilae. Here we’ve left Aquila, hop­ping next door into Scu­tum. De­spite be­ing lo­cated against rich Milky Way starfields, these aren’t that ob­vi­ous through smaller aper­tures, re­sult­ing in the clus­ter ap­pear­ing with sur­pris­ingly few field stars around it. It con­tains around 71 mem­bers, which to­gether give it an in­te­grated mag­ni­tude of +9.2. A 6-inch scope re­veals a mostly hazy patch with just a few stars show­ing in­di­vid­u­ally. Six of these form a dis­tinc­tive wedge-shaped as­ter­ism that can be used to pos­i­tively iden­tify the clus­ter. Ĵ SEEN IT

6 M11

Our fi­nal tar­get is M11, the Wild Duck Clus­ter. It re­sides in Scu­tum and can be found by ex­tend­ing the curve formed by Lambda and 12 Aqu­liae through mag. +4.8 Eta (d) Scuti. M11 is 1.5º west­south­west of Eta and should be just vis­i­ble to the naked eye. A 6-inch scope shows around 150 stars, and as you in­crease the aper­ture the view gets steadily more breath­tak­ing, with many stars ap­pear­ing clumped into knots and strings. Its name comes from a V-shape of stars that re­sem­bles the pat­tern formed by fly­ing wild ducks. In to­tal this clus­ter, 6,000 lightyears dis­tant, is es­ti­mated to con­tain 2,900 stars, 500 of which are brighter than mag. +14.0. Ĵ SEEN IT

Clumps and chains of stars be­come ap­par­ent in the Wild Duck Clus­ter through larger in­stru­ments

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