Starry-eyed in the Southern Hemisphere


A city of almost 7 million people with an attendant level of light pollution isn’t the optimum place to take in the night sky, but I can’t stop doing that here anyway. Because for the first time in my 52 years on this planet, I don’t see the same stars and constellations when I look up after dark.

The Southern Cross hangs in the sky over a building on Rio de Janeiro's waterfront, with Rigil Kentaurus (Alpha Centauri) and Hadar (Beta Centauri) visible below and pointing up at the Southern Cross.

The obvious attraction above is the Southern Cross, a constellation iconic enough to figure in the flags of Brazil, Australia, New Zealand and other Southern Hemisphere nations. I first spot it as a slumped triangle, and after a few minutes for my eyes to adjust I can make out its fourth-brightest star and then the fifth that completes the constellation formally known as Crux.

There’s also the closest star system visible to the unaided eye–which I knew as Alpha Centauri AB as a younger space nerd but now see in my phone’s sky-map app as Rigil Kentaurus.

(Until writing this post, I did not realize how complex stellar nomenclature can get or how it had changed recently as the International Astronomical Union has worked to get more systematic about it.)

The 4.3 light years and change separating our sun from that binary star might as well be walking distance in our galaxy; the closest star visible in the Northern Hemisphere, Sirius, is twice as far away. Meanwhile, Beta Centauri, the triple system visible as a bright star near Rigil Kentaurus (and through which you can visualize a line pointing to the top of Crux) is another 386 light years distant.

I’ve seen less of the brightest star in this hemisphere because Canopus sits lower in the sky here. Above the sky, however, Canopus is unmissable enough to serve as a reference point for star trackers on spacecraft that have helped steer some of them out of the solar system.

Looking up at night far from home on this trip (note: expenses covered by Web Summit in return for my moderating two panels at the new Rio edition of their conference) takes me back to doing the same thing at home in rural New Jersey decades ago, where a clear summer night would treat me to a sky full of stars, with the Milky Way a glowing path arcing overhead behind them. That sight is one thing I still miss about country life, and it remains something I look forward to seeing anew when I have an overnight stay somewhere far from city lights.