President's Corner

A Northern Hemisphere Astronomer in the South
by Michael Watson, President

The southernmost point in Canada is Fish Point Provincial Nature Reserve on Pelee Island, which is halfway across Lake Erie to the United States and 75 km almost due east of Toledo, Ohio.  From this position, at north latitude 41.7 degrees, Canadian starwatchers can see the celestial sphere down to declination 48.3 degrees south, but no further.  This means that almost 17 percent, or one-sixth, of the sky is permanently below the horizon and invisible as seen from that location.  If we consider that decent views require objects in the sky to be at least ten degrees above the horizon, then almost 24 percent of the sky either is invisible or cannot properly be observed from Canada.  (The area of a sphere that is “above” or “below” – or in astronomical terms, north or south of – a particular angle or latitude is often referred to as the “spherical cap”. The formula for the area of a spherical cap is 2 x Pi x R2 x (1- SIN latitude), where R is the radius of the sphere.)

            What does this mean for Canadian astronomers who are homebodies, and never leave the country? A large portion of the sky either is permanently hidden from view by the bulge of planet Earth to the south of us, or is observable only under unfavourable, close-to-the-horizon conditions.  From Canada we can never see the first magnitude stars Rigel Kentaurus and Hadar (Alpha and Beta Centauri), Peacock (Alpha Pavonis), Achernar (Alpha Eridani) and Canopus (Alpha Carinae), as well as the lovely asterism in the constellation Crux known as the Southern Cross and Proxima Centauri, the closest star to us other than the Sun.  Hidden from view too are some famous deep-sky objects that many northerners know only from photographs, including the Large and Small Magellanic Clouds, the wonderful Eta Carinae Nebula (NGC3372), the Southern Pleaides (IC2602), the dwarf galaxy remnant Omega Centauri, and the bright globular star cluster 47 Tucanae.

            At least as frustrating for us northerners is that the centre of the Milky Way, in the constellation Ophiuchus at right ascension 47h 45m, declination -29° 00’, never gets more than 19 degrees above the horizon for southern Ontarians, and never more than 10 degrees up in the sky for skywatchers observing, for example, from the RASC Calgary Centre’s Wilson Coulee Observatory.  The central bulge of our home galaxy is therefore tantalizingly ill-situated for our visual contemplation.

            I had my first opportunity to look skyward from the southern hemisphere in June 1983, when I joined an expedition out of London to observe the very long (5 minutes, 9 seconds) total solar eclipse of June 11 that year from the north coast of the island of Java in Indonesia.  I will never forget my first view of the southern sky the night before the eclipse, when I camped out under the stars at latitude 6.9° south, and saw the central bulge of the Milky Way rising almost straight up from the east-southeastern horizon as the sky darkened.  By midnight, when it was centred on the meridian 67° high in the sky, the Milky Way stretched from horizon to horizon, with the centre almost frighteningly bright above me.  Adrenaline was rushing and my heart was pounding.  For months – even years – I had imagined this view, but the reality overwhelmed me and surpassed anything that I had imagined.

            But there was something else, and it was discombobulating.  I was so used to seeing the familiar star patterns of Scorpius and Sagittarius close to the horizon that I couldn’t recognize them when they were so high in the sky above me.  And the northern constellations of Boötes, Corona Borealis, Hercules, Lyra and Cygnus all seemed upside down to me, since I had to face north to get a good view of them, rather than south as I did in Canada.

            After the eclipse I went to Australia, and for a few nights visited and observed with Tom Cragg, the Chief Night Assistant at the Anglo-Australian Observatory in Coonabarabran, New South Wales. The location is without doubt the darkest observing site that I have ever experienced. The dark green of the surrounding eucalyptus trees prevented any reflection back into the sky from the meagre skyglow. I couldn’t see even the faint outline of my hand in front of my face, let alone my telescope and Schmidt camera, without using a red light.

            From the -31° latitude of the observatory, the centre of the Milky Way was now a little north of the zenith. When I turned around to the north to look up, the familiar teapot shape of the brightest stars in Sagittarius, and the head and tail of the scorpion in Scorpius, vanished; I couldn’t make them out at all. Only when I turned south and craned my neck backward a little to the north did they pop back into view. This taught me a valuable lesson that has remained with me forty years later: We recognize a visual pattern not only by the relative positions of the points of the pattern with respect to each other, but also by the orientation (i.e., angle) of the entire pattern in front of us. And it takes only a few tens of degrees of rotation before a previously familiar pattern becomes difficult for us to spot, bordering on unrecognizable.

            Since that first visit to an antipodal latitude in 1983, good fortune has taken me south of the equator nine more times, and often to the Outback of Australia. Every time, the overwhelming impression that I have is how majestic the Milky Way looks as seen from that vantage point. Only from the south can we see the thin disk of the galaxy on both sides of the central bulge splayed across the sky. When we see it from this perspective, it is so obvious that the Milky Way is the same type of object as are the distant galaxies that we know so well, such as M31 in Andromeda. A long time ago I heard, and I summoned up this memory when writing this column, the theory that if the centre of the Milky Way were located as far north on the celestial sphere as it actually is in the south, then northern hemisphere astronomers would have concluded decades or even centuries earlier that the Milky Way and these other objects were of the same type. The so-called Great Debate of 1920 between Harlow Shapley and Hebert Curtis about the nature of the Milky Way, “spiral nebulae” (as they were called then), and the dimensions of the universe might have been well and truly settled long before.

            My experiences south of the equator have brought me to agree so strongly with the view that every serious astronomer, and even the perhaps less obsessed and more casual stargazer, who lives in the northern hemisphere, should endeavour to travel south of the equator at New Moon at least once in that person’s lifetime to behold the splendour of the celestial sphere from that vantage point. There is so much to see, and in which to revel, away from home.

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Monday, March 18, 2024 - 11:13pm