Constellation of the Month - Circinus

Albert Brakel

Circinus, the Draftsman's Compass, is a narrow constellation with no readily recognizable pattern, and is awkwardly sandwiched between Centaurus and Triangulum Australe. Other adjoining constellations are Norma and Lupus to the north, and Musca and Apus in the south. It is a constellation that didn't really need to be invented, as its stars could easily have been allocated to the neighbouring groups.

The easiest telescopic object in the constellation is the double star Alpha Circini (14h 42.5m, -64 59'), which forms a right-angled triangle with Alpha and Beta Centauri. With a 16" spacing, the mag. 3.2 and 8.8 components can be separated even with 50x. Their colors are given as pale yellow and red, not a particularly common color combination, but unfortunately the red secondary was too faint to show its color with 20 cm aperture. The system is about 65 light years away.

Gamma Cir (15h 23.4m, -59 19') is a more recalcitrant double. It would not split under average seeing, though with 235x it seemed to begin to elongate. Hartung gave the separation of the mag. 5.1 and 5.5 stars as 1.1", but they have now closed to a tighter 0.8". Ross Gould has split it under good conditions with a 7" refractor (you do have one lying around the house, don't you?). Try it with the Oddie.

At the other end of the constellation, h 4632 (13h 58.5m, -65 48') is easier, and is an orange and white unequal pair (mag. 6.2 and 10.0) comfortably split by 77x. Though widely separated (6.4"), the secondary is dim and not obvious at first, especially in moonlight.

Nearby to the SW is the planetary nebula NGC 5315 (13h 54.0m, -66 31'), following a pale yellow star by 4'. It is pale bluish and barely discernible as a disk, and dims greatly with direct vision, unlike nearby stars of similar brightness. It is made more obvious with an OIII filter, which dims the stars but not the nebula.

ESO 97-G13 (14h 13.2m, -65 20'), a bit over 2 deg. NE of NGC 5315, is a mag. 10 spiral galaxy that is visible only because of a window in the general dustiness of the Milky Way. The dimmest of smudges, it needed a Lumicon Deep Sky filter to just detect it in the suburban sky. Definitely not an object for small scopes or undark skies. I only mention it because it is unusual to see a galaxy only 4 deg. from the galactic plane, and because it was first reported only in 1977, after being found on a plate taken with the Uppsala Schmidt at Mt Stromlo.

Most of the objects described above are not particularly easy for moderate apertures, but I hope you enjoy the challenge anyway.