DEEP-SKY TOUR
We begin explore the celestial treasures in the constellation of Puppis, the Poop Deck
1 NGC 2452
We start low in the constellation of Puppis; NGC 2452 is a planetary nebula 2.4˚ south of mag. +3.3 Asmidiske (Xi (x) Puppis). The nebula is listed at mag. +12.2 and although it can be seen through smaller scopes, requires at least 250mm of aperture to start to see properly as a faint, mostly featureless oval. A 300mm scope shows brighter patches to the north and south of the main nebula. NGC 2452 appears quite large, with an apparent size of 30x20 arcseconds. SEEN IT
2 M93
M93 is a mag. +6.2 open cluster, 1.5˚ northwest of Asmidiske. This low declination Messier is a glorious object; 30 members packed into a 10-arcminute region through a 150mm instrument. Larger instruments reveal an object expanded to an apparent size just over 20 arcminutes; M93 has over 100 members.
Located at a distance of 3,600 lightyears, the cluster mostly consists of blue giant stars with a small number of red giants. Visually the cluster appears wedge-shaped, two brighter stars sit close to the tip of the southwest pointing wedge. SEEN IT
3 NGC 2440
NGC 2440 is listed at mag. +9.4 and is bright enough for a small scope. Sitting in a region of sky devoid of bright stars, one way to locate it is to extend the line from Sirius through mag. +4.3 Iota (i) Canis Majoris for 3.8 times that distance again. Alternatively, head 6.3˚ north of Asmidiske, then drift 1.6˚ west. A 250mm scope shows an elongated 30x20 arcseconds object which loses its stellar appearance around 100x magnification; the central region appears 15 arcseconds across and circular. A 300mm scope at 400x magnification reveals the central area consists of two bright lobes arranged at right angles to the long axis of the now 40x20 arcsecond glow of the main nebula. SEEN IT
4 M46
M46 is the easternmost of two close clusters in northern Puppis, the other being M47. M46 lies 3.4˚ north of NGC 2440, and shines with an integrated magnitude of +6.1; theoretically visible to the naked eye from a good, dark site. This is a rich open cluster roughly 20 arcminutes across. Over 70 stars are visible through a 150mm scope, spread uniformly across the area with no real central condensation. A mag. +5.0 red star, HIP 37379, sits half-a-degree southwest of the centre of M46, and this can be used to navigate to target 5. SEEN IT
5 NGC 2438
The planetary nebula NGC 2438 appears embedded in M46. If you can visualise where the approximate centre of M46 is visually, imagine the line between the mag. +5.0 red star HIP 37379 mentioned earlier, and NGC 2438’s centre. Keep going for around 5 arcminutes to reach the nebula. The distance between HIP 37379 and M46’s centre is 34 arcminutes.
NGC 2438 doesn’t share the same radial velocity as M46 and is thought to be unrelated to the cluster. Its appearance within M46 is simply a line-of-sight effect. In reality, NGC 2438 is a foreground object around 1,370 lightyears away, a little over a quarter of M46’s 4,920-lightyear distance. It shines at mag. +10.8 and has an apparent size of 1.1 arcminutes. SEEN IT
6 M47
Open cluster M47 is 1.3˚ west and a fraction north of M46. At mag. +4.4, it’s an easy naked-eye object. M47 exhibits a good distribution of star brightness. The brightest star lies on the western side and is a double, with components of magnitudes +5.7 and +9.7 separated by 20 arcseconds.
A 150mm instrument shows around 50 stars within a region 30 arcminutes across. Increased aperture ups this number, a 250mm scope revealing about 80 stars.
This lovely Messier was once considered lost. Although cluster NGC 2422 was known, Messier’s coordinate offset from seventh magnitude 2 Puppis, 2.2˚ to the east, pointed to nothing. It took Canadian astronomer TF Morris to realise that the signs on Messier’s offsets were wrong. Switch signs and it’s clear that NGC 2422 is actually M47. SEEN IT