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Southern Cross - May 2000

• Constellation of the Month - Canes Venatici
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Constellation of the Month - Canes Venatici

Michael Nelmes

Canes Venetici, the Hunting Dogs (of adjacent Bootes the Herdsman), is one for the northsiders, none of it rising more than 25 degrees above Canberra's north horizon. With the naked eye only one or two of its stars are easily seen from here. It's known mainly for its Messier objects, mostly galaxies (see Burnham's Vol. 1 for photographs of nine of them) which although relatively bright suffer from atmospheric extinction; and a few nice binary stars which might be best seen with a small to medium scope to minimise atmospheric blurring.

Alpha Canum Venaticorum (Cor Caroli or Charles' Heart, named by Edmund Halley who was evidently keen to keep in favour with King Charles II) - 12h56m, +38deg 19min. A very attractive binary star of mags. 3 and 5.6 separated by 19 arcseconds, which I saw as white (primary) and mauve (secondary), despite Hartung's description as pale yellow, and Burnham's historical account of almost every colour of the rainbow having been seen in this pair. The primary is the prototypical example of a "magnetic spectrum variable". Alpha marks the position of the mythological hunting dog Chara; the other dog is Asterion (Beta).

M3 (NGC5272) - 13h42m, +28deg 23min. A fairly bright (mag. 6) globular cluster easily visible with my 7x50 binoculars. The 4.5-inch telescope shows it as mottled with a broadly condensed core. It's the third brightest globular in the northern sky.

M51 (NGC5194) - 13h30min, +37deg 12min. The famous 8th magnitude Whirlpool Galaxy was the first spiral nebula to be recognised as such, which in the 1850s it was thought to be a solar system in the making. However, a 4.5-inch scope peering through the murk 7 degrees above the horizon doesn't compete with Lord Rosse's overhead view with his 72-inch. Distance is some 35 million light years, and type Sc. Photos of the Whirlpool and its small attached satellite galaxy NGC5195 are in profusion - see for example the cover of Burnham's Volume 1 - and make it a good candidate for the 'definitive' spiral galaxy. The two nuclei are pointlike through the telescope. M51 is only 3.5 degrees from the end handle star of the Big Dipper which grazes along Canberra's north horizon.

M94 (NGC4736) - 12h51m, +41deg 06min. This mag.9 face-on spiral galaxy could only just be seen through the 4.5-inch scope, although it's described as bright and very compact. Distance is around 20 million ly.

M63> (NGC5055) - 13h16m +42deg 2min. The Sunflower Galaxy, again a spectacular photographic object, but visually quite dim at 10th magnitude due to low surface brightness. Its multiple, tightly coiled arms are discernible only in large scopes. Distance is thought to be about 35 million ly.

M106 (NGC4258) - 12h19m, +47deg 18min. A 9th magnitude, somewhat tilted (20 x 6 arcminutes) spiral galaxy with a relatively bright, elongated nucleus.

2 Canum Venaticorum - 12h16m, 40deg 40min. A binary of magnitudes 6 and 8, separated by 11 arcseconds. Hartung calls them orange and slate-blue coloured.

Hope you enjoy this selection. If you don't have a low north horizon, take your scope up a hill and have a look at some these well-known objects which are often overlooked by Canberrans.