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Southern Cross - October 1999


Constellation of the Month - Vulpecula & Sagitta

Michael Nelmes

These neighbouring northern constellations, sandwiched between Cygnus and Aquila, are quite small so we've combined them for this month. Situated in the Milky Way (though not a dense part of it), double stars, variables and planetaries feature numerously, and galaxies poorly. The planetaries, except the Dumbbell, are below mag. 11. At this time of year these two constellations are for early evening observing.

Vulpecula is not some supernatural being from Transylvania, but a fox. Alphabetically it's the last constellation, but gets my vote for the coolest name. You might remember the article some issues back on a talk given by Jocelyn Bell-Burnell, discoverer of the first pulsar in 1967; well, it was in Vulpecula that she found it. It's also home to two household objects, the Dumbbell and the Coathangar.

NGC6802 (19h25m, +20º11'). Other names: The Coathangar; Collinder 399 (another household object?); Brocchi's Cluster. This is one of those quaint little asterisms that is a "must see". Best seen through binoculars or your finder, six stars of mag. 6-7 form a dead straight line, and out of the middle emerges the coathangar's hook.

NGC6853 (19h59.6m, 22o43'). M27; Dumbbell Nebula. Being perhaps the closest planetary nebula, it's also the largest (6 x 4.5 arcminutes, corresponding to more than 2 light years - half the distance from here to Alpha Centauri!) and brightest (mag. 8) and can be seen in binoculars. Distance is c.900 light years. Through the 18cm refractor with a half moon up, it is basically rectangular with the south half slight brighter and better defined. Photographs show it to be hourglass-shaped. I had an equally good view with my 4.5-inch Newtonian at 72x and no Moon.

NGC6940 (20h34.5m, +28o18'). Use a large aperture and wide field for this large open cluster; most stars are very faint but with some brighter for interest, spread over 20 x 15 arcminutes. "Delicately beautiful", wrote Hartung.

Sagitta the arrow is the third smallest constellation and also has a few attractions:

NGC6838 (19h53.6m, 18deg47.1m). M71. Although appearing dense enough to be a globular, this mag. 9 cluster is probably an open one. Diameter is 6 arcminutes, distance 18,000 light years. In the 4.5-inch Newtonian it's dim and mottled but not properly resolved and with no central condensation.

U Sagittae (19h16.6m, +19deg31m (1950)). An eclipsing variable that is easy to follow because of its short period (3 days 9 hours) and large variation (mag. 6.4 to 9.1). See Burnham's p.1531 for a finder chart.

Zeta Sagittae (19h49m, +19o08.7'). A mag.5 yellow star with a mag. 9 reddish companion at 8 arcseconds. A nice sight at low power, the secondary being clear through the 18cm refractor, dim through the 4.5-inch Newtonian. Don't expect to split the binary primary (0.2 arcseconds).

Theta Sagittae (20h10m, +20o55.1'). Another good one for low powers (mags. 6.5 and 8.5 at 12 arcseconds). The 18cm refractor with 2-inch 35mm eyepiece shows it in an attractive star field.


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