Sand and Stars

Pyxis, the Instrument that Changed the World

Pyxis’ three bright stars in a line symbolize a truly historic instrument that changed the world

15 March 2022

Pyxis may be small and faint, but what a mighty instrument its line of three fourth magnitude stars represent – the mariner’s compass. Prior to the invention of the compass it was better to be a penguin than a seafaring navigator. Sailors relied on the sun or stars, but put humans in a deep fog and they go in circles, hopelessly lost. Getting hopelessly lost in treacherous seas in a deep fog was a terrible danger, often with disastrous consequences. On the other hand, Fiordland penguins, found in the waters of Antarctica around the Southern Islands, navigate treacherous seas safely up to 6,800km on the round trip from their breeding site in New Zealand. 

Although the history of the compass started more than 2000 years ago during the Han dynasty (202 BC – 220 AD), it was not used for navigation, but for geomancy and fortune-telling by the Chinese. The first reference to the use of the compass in navigation was by the Chinese around AD 1100 in the book, Phing-Chou Kho T’an, which included information about sailing ships and customs at sea.  The so-called “south-pointing fish” was a wooden fish with a magnetized iron needle within it, that floated in a bowl of water. (The south was the preferred direction of the Taoist trigrams. It was the direction of the sky, while the north was considered inauspicious.) Later, a dry compass version evolved in the shape of a turtle. Lodestone was embedded in its carved wooden body and balanced on a bamboo needle, which allowed it to rotate freely.

A Chinese south-pointing fish

Alexander Neckam (1157-1217), an English theologian and poet, produced the earliest European account of the compass. In his De utensilibus (On instruments, 1190) he noted how a ship, among its other stores, must have a needle placed above a magnet (mounted on a pivot), which would revolve until its point looked north, and guide sailors in murky weather or on starless nights. 

Without the invention of the compass, we wouldn’t have had the Age of Discovery which yielded unprecedented discoveries between the 1400s and 1600s and forged interactions between Europe, Asia, and the New World that forever altered the course of history. 

A box compass that once belonged to Christopher Columbus. Image credit US Naval Institue

As a child in the 1960s a compass played an enormous part in my childhood age of discovery… my father took us children on wonderful adventures into the most remote parts of  Mozambique, navigating by his trusty compass. I can remember when I learnt how to navigate with a compass. I was eight years old and my father took my brother and I on a hell of a trek through the mangrove swamps and tidal flats in Sofala Mozambique to find the ruins of a 16th century Portuguese fort. He taught me how to navigate using his compass and all these decades later I can still remember the thrill and awe of holding in my hand the little device that always pointed north. 

All that remains of the fort are these crumbling stone remnants, ravaged by sea, sand, wind and time and disappearing into a shifting sandbar…

Image credit Jules Frémeaux Wikimedia Commons
Image credit Jules Frémeaux Wikimedia Commons

When Lacaille split the huge and magnificent ship Argo Navis into Carina, Puppis  and Vela, he appropriated the stars that had been catalogued by Ptolemy as lying in the mast of the ship and invented Pyxis. However, Pyxis isn’t part of the dismantled ship; Lacaille showed it separately from Argo on his map and in his catalogue. His original depiction of it was published in 1756 under the French name la Boussole, and in the notes accompanying the chart he described it as ‘le Compas de mer’. On the second edition of his chart in 1763 Lacaille Latinized its name to Pixis Nautica (sic), which was subsequently shortened, with amended spelling, to just Pyxis. (Interestingly, in 1844 John Herschel suggested renaming Pyxis as Malus, the Mast, which would have returned the stars to the dismantled ship but the new name, thank goodness, was never accepted.)

Pyxis on Chart XVIII of the Uranographia of Johann Bode (1801)

Small, faint and seemingly insignificant these few stars symbolize a truly historic instrument that changed the world and holds so much meaning and significance for many different reasons. And one can never get lost literally or figuratively with a compass at hand. 

Observing Pyxis

16″ f/5 Dobs; 150x, 228x and 333x 

Pyxis Globular Cluster

RA 09 07 57.7   Dec -37 14 17   Mag 12.9   Size 4′ 

The Pyxis globular clusters is barely visible in this image as a slight increase in the faintest stars at the centre of the field. DSS image

Discovered by Weinberger in 1995, the Pyxis Globular Cluster lies a staggering 130,000 light-years from Earth. In a 1995 paper, astronomers Irwin,  Demers and Kunkel wrote, “The Pyxis cluster appears to be somewhat younger than the majority of halo Galactic globulars, is of intermediate metallicity, and lies some 42 kpc from the Galactic center. An intriguing possibility is that Pyxis is a detached member of the cluster system of the Magellanic Clouds, since it lies in the plane of their orbit and at a similar distance. With this in mind, it is of note that the color-magnitude diagram of Pyxis is similar to that of the outer halo LMC cluster, ESO 121–SC03 (Mateo, Hodge, & Schommer 1986), which has an anomalous age relative to other LMC clusters and has been postulated to be a captured SMC cluster. A radial velocity is urgently needed to examine the possibility of Pyxis being a Magellanic Cloud cluster captured by the Galactic halo.” 

What a fascinating globular cluster to observe. But alas, not even so much as a hint of it. But then, one look at the image and I hadn’t expected to see anything… but I looked nonetheless; it’s always nice to know one’s eye is passing over a truly fascinating object that is remaining steadfastly invisible.

T Pyxidis – Recurring Nova 

RA 09 04 41.5   Dec -32 22 47   Mag 15.5    

T Pyxidis. DSS image

T Pyxidis is one of the few known recurrent nova and presently holds the record for the greatest number of observed outbursts with five recorded to date. There are currently only ten recurrent novae known. T Pyxidis was observed erupting in 1890, 1902, 1920, 1944, 1966 and 2011. In these outbursts, T Pyx took about 20 days to reach 7th magnitude or so and remained 8th mag or brighter for about two months, before returning to its normal 14th magnitude state. Every night Pyxis is visible in the sky I cast a binocular look in T Pyxidis’ direction; what a joy it would be to catch this recurrent nova going into outburst or better yet, ending its life as a Type 1a supernova!

NGC 2627 – Open Cluster

RA 08 37 14.2   Dec -29 57 07  Mag 8.4   Size 10.4′ 

NGC 2627. DSS image

This is a lovely cluster – rich in stars with the lovely haze of unresolved stars and set in a background itself rich in stars. Around 60 mag 11-15 stars are resolved in a 10’x5′ region elongated E-W. The cluster lies 4′ SW of a mag 5 star.

NGC 2658 – Open Cluster

RA 08 43 28.3   Dec -32 39 43   Mag 9.2   Size 7.3′ 

NGC 2658. DSS image

Another pretty cluster with around 30 mag 12 and fainter stars resolved in a 10′ area, set against the glow of unresolved stars. Three mag 11 stars are off the south, southeast and east side and there’s what looks like a double or perhaps small knot of stars on the northern side.

NGC 2613 – Galaxy

RA 08 33 22.8   Dec -22 58 25   Mag 10.4   Size 7.59′ x 1.7′   SB 12.9   PA 113°

NGC 2613. Image credit ESO/IDA/Danish 1.5 m/R. Gendler, J.-E. Ovaldsen, C. Thöne and C. Féron

This edge-on galaxy is the brightest galaxy in Pyxis.  And it is certainly a pretty galaxy, not least because it lies immersed in a beautiful field of stars. It appears as a beautiful fairly bright, fairly large, silky grey glow oriented WNW-ESE. It brightens somewhat to the centre and its silky glow on the edges fade away rapidly into the starry background. A mag 12 star lies at the west edge of the halo.

I was musing while looking at this galaxy how infrequently I look at a galaxy not as small and beautiful glow in the sky but as a large aggregate of stars, gas, dust, planets, rocks, dark matter, and perhaps weird and wonderful life forms… existing by the hundreds of billions throughout the observable universe.

NGC 2818 – Open Cluster and Planetary Nebula

RA 09 16 10.6   Dec -36 37 26    Size 9.4′

NGC 2188. DSS image
NGC 2818A. Image credit Hubble

NGC 2818 is an open cluster and NGC 2181A is a superimposed planetary nebula. It would be grand to observe an open cluster with the ghost of one of its members lying among its stars, but in a 2007 paper, astronomers Daniel Majaess, David Turner and David Lane concluded that the evidence implied a spatial coincidence rather than a physical association for NGC 2818, and places the planetary nebula in the foreground. 

But what a lovely line of sight pair of objects! The fairly rich but faintish open cluster appears as ~40 resolved mag 12-15 stars set against the soft haze of  unresolved stars. But the background sparkle certainly makes a lovely backdrop for the PN which lies on its western side. It appears as moderately bright and irregularly shaped – around 1.0’x0.8′ in size – and elongated roughly N-S. It responds very well to the UHC filter and its edges are crisp, with it appearing brightest along its south and southwest edges. The center is slightly darker but the darker centre isn’t well defined; it just darkens towards the centre. No sign of a central star.

IC 2469 – Galaxy

RA 09 23 00.9   Dec -32 26 58   Mag 11.2   Size 4.7’x1.0′   SB 12.6   PA 37° 

IC 2469. DSS image

This edge-on galaxy appears moderately bright and very elongated SW-NE. It is sharply concentrated with a bright core. fades out beautifully to tips that just disappear into the starry background. A mag 12 star is superimposed on the SW end. 

NGC 2663 – Galaxy

RA 08 45 08.1   Dec -33 47 41   Mag 12.3   Size 3.7′x2.5′   SB 3.2   PA 110° 

NGC 2663. DSS image

This galaxy lies in a gorgeously rich star field – there really is something to be said for seeing the faint glow of a distant galaxy against a plethora of sparkling Milky Way stars! The galaxy appears fairly faint, moderately large and elongated WNW-ESE. It has a beautiful core which is evenly concentrated down to a non-stellar nucleus, and its halo is a soft haze that dissolves into its starr background. 

NGC 2883 – Galaxy

RA 09 25 17.5   Dec -34 06 11   Mag 13.1   Size 2.8’x0.9   SB 13.6   PA 176°

NGC 2883. DSS image

This galaxy appears faint, moderately large, and elongated N-S. Its glow is very interesting – appearing irregular and oddly mottled as if the galaxy is somewhat discombobulated! Averted vision shows three very faint stars superimposed on its glow.

NGC 2717 – Galaxy

RA 08 57 01.0   Dec -24 40 25   Mag 12.3   Size 2.1’x1.5′   SB 13.5   PA 10°

NGC 2717; ESO 496-22 lower left. DSS image

This galaxy appears as a moderately bright and fairly small oval oriented SSW-NNE. It has a beautifully bright core, 30″ ãnd a stellar nucleus. Its halo is the gauziest glow that simply fades away into the surrounding sky. A mag 11 star lies 2.1′ ENE of centre. Lovely field of stars… and the galaxy ESO 496-22 lies ~5′ SSE.

NGC 2888 – Galaxy

RA 09 26 19.6   Dec -28 02 06   Mag 12.6   Size 1.4’x1.0′   SB 13.0   PA = 158°

NGC 2888. DSS image

This galaxy appears faint, small, very slightly elongated NNW-SSE, with an even glow that brightens somewhat to the centre.

NGC 2821 – Galaxy

RA 09 16 47.9   Dec -26 48 58  Mag 13.0   Size 2.0’x0.4′   SB 12.8   PA 100° 

NGC 2821. DSS image

This galaxy appears as a faint and fairly small streak of pale light elongated E-W. It is a smooth glow with the very slightest brightening to the centre.  A mag 13 star is attached to the glow just NW of the centre.

NGC 2772 – Galaxy

RA 09 07 41.8   Dec -23 37 17  Mag 13.4   Size 1.5’x0.9′   SB 13.6   PA = 163°

NGC 2772. DSS image

I really do love an edge-on galaxy; there is something so indescribably elegant about them. This galaxy appears fairly faint, moderately bright and elongated NNW-SSE. It has a beautifully smooth and even bulging core and much fainter extensions that fade rapidly into the surrounding sky. The galaxy lies in a very pretty star field.

Copyright © Susan Young 2022