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Southern Cross - May 1999

• Constellation of the Month - Pyxis
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Constellation of the Month - Pyxis

John Morland

Pyxis, the compass, is a rather small faint constellation, located at the stern of the old constellation, the ship Argo. It lies to the east of the more famous (and more interesting) constellation, Puppis. All but one of its stars are fainter than magnitude 4 (brightest is mag 3.7).

Pyxis was invented by the French astronomer Nicolas Louis de Lacaille (1713-1762) who was the first person to comprehensively map the southern skies. He directed an expedition to the Cape of Good Hope in 1750-54 where he systematically surveyed the southern skies listing over 10,000 stars. Lacaille introduced 14 new constellations representing scientific and artistic instruments; Pyxis is one of these.

In co-ordinate terms, Pyxis lies around 9h RA and -30 degrees declination. It does not hold any famous objects, certainly none that you would use to show off the wonders of the southern sky to your neighbour. However, that is not to say that there is nothing to see for the amateur astronomer who is looking for something a little different, that is not a "big bright thing" object, and who has a telescope of a reasonable aperture and/or possesses some Horse Head nebulae vision. (A quick note to new members - for some reason which escapes me, this Society has permanently linked me with the Horse Head Nebula in Orion. This is evident in the design of the John Morland Nebulous Prize shield on display in our library at Don's Dome). Anyway here are some objects I managed to have a look at:

For the nova buff, T Pyx (9h 05m, -32 degrees) is a recurrent nova. It has undergone 5 eruptions, 1890, 1902, 1920, 1944, 1966. It is normally magnitude 14, but during an eruption it brightens to magnitude 6 - 7 . I had a look for this in my 12.5" and did not see anything obvious.

Burnham 205 (RA 8h 33.1m, Dec. -24o 36') is difficult to split at ½ a second separation. I am not sure I did it at 290X, it looked elongated (maybe). The components are even, mag. 6.9 and 7.0.

Burnham 208 (8h 39.1m, -22o 40') is easier (not easy) as separation is 1 second, components are uneven at 5.3 and 6.6 mag. Don't be afraid of high power for this.

Beta Pyxidis (8h 40.1m, -35 18' 30") looked like a bright yellow/orange in my 12.5". I thought I saw a faint double at 290X (6 mm Plossl) but I think it was an optical illusion.

One further double, h 4188 (9h 03.3m, -33o 36'). Forget the others, this is the one! Fairly wide at 13", components are 6.7 and 7.4 mag., pale yellow colour. What sets off this pair is a beautiful field of fainter stars. If you must, try and split the fainter of the two - I did not want to spoil the view so I did not attempt it.

NGC 2618 (9h 16m, -36o 38'). This is a star cluster with a planetary nebula in it (not to be confused with the more impressive M46 in Puppis, a star cluster with a planetary nebula in front of it) and about 10 000 light years away. I had some difficulty in finding it, but managed to star hop from Eta to Gamma Pyxidis with a very low power eyepiece (50 mm Plossl) and then come to this faint starry field. Switching on my Horse Head vision, slowly something loomed into view - a cluster only 7' across with a faint round smudge in the middle. I increased the power to 115X (15 mm Teleview wide angle eyepiece) which brings it out nicely. I tried all my filters on it and I thought the Deep Sky was the best, UHC if you want to favour the planetary nebula. If you want the nebula and nothing but the nebula, then the OIII filter is for you.

NGC 2613 (8h 33.4m, -22o 10.4') is a 10.4 magnitude edge-on spiral galaxy of 4' in length, about 60 million light years away. Same as above, I star hopped the opposite way (Gamma to Eta and did a 45-degree turn to the north). I came to a starry field, looked around and noticed this small spindle smudge looming in. Again 115X bought it out well, the Deep Sky filter helped a bit (but that could be a matter of opinion).

Overall I enjoyed looking around this constellation. It offers more of a challenge than a lot of others, and does come up with some quite nice objects. However I would suggest you do not bother your neighbour with these, or someone you are trying to convince of the glories of the Southern Sky.