Urban Astronomy in the Southern Hemisphere

Australian Flag

This week I had the privilege of working for four days in Sydney, Australia and the weather was clear, so I had a chance to experience the daytime and nighttime sky from a wholly new perspective. When you view the sky from south of the equator the sky is viewed in an entirely new light, and the differences in view in the southern hemisphere compared to the northern hemisphere are many.

Daytime: in Sydney, the Sun tracks across the northern half of the sky, not the southern. In San Francisco we know that the southern exposure of a building or garden gets more Sun, but in Sydney the northern exposure gets all the Sun. When you are simply walking around the city the effect is incredibly subtle. But for me as an amateur astronomer, it was disorienting at times. I enjoyed the experience of looking for shadows and light in a new way and had to think through why and how light and shadows appeared as they did. 

Nighttime: this is where the Southern Hemisphere is amazing. At night the entire sky feels new. I was in Sydney all week and had to put up with city lights and a bright Moon, so that afforded me a chance to get introduced to only some of the night sky with just the brighter objects available for viewing. Nighttime urban viewing presented me with four levels of discovery. 

1. Uniquely southern stars and constellations 

The immediate thing one notices in the southern sky is the Southern Cross and the two ‘pointers’ in Centaurus, Alpha Centauri (Rigil Kent) and Beta Centauri (Hadar). This bright grouping is high in the south in May. There are other nearby constellations that are fainter in an urban setting, but the Southern Cross (Crux) and Centaurus are very obvious, and to my eye are the most unusual and captivating objects. The Southern Cross is so special to the region, it is prominently featured on the Australian and New Zealand flags. 

2. Ecliptic / Moon and Planets / Zodiac 

In stark contrast to my view of the sky in San Francisco, the ecliptic traverses not the southern sky but the northern sky from Sydney, and the zodiac constellations on the ecliptic are quite differently positioned. For example, Scorpius and Sagittarius are summer constellations from my home in San Francisco and are low on the horizon, never getting too high in the sky on summer evenings. From Sydney, these two constellations are much higher in the sky and are upside-down from my point of view. The Moon and planets, by virtue of their following the same ecliptic track across the sky, are disorientingly located in the north, again breaking convention and obligating the studied observer to rethink his bearings. 

3. Equatorial constellations viewed from the south 

The region on and near the celestial equator is lined with bright stars and well-known constellations. We normally view this in the northern hemisphere looking toward the south so equatorial constellations such as Orion have a definite ‘up’ and ‘down’ that we expect. When you move to the southern hemisphere, the view of the celestial equator and its constellations in inverted so all of the familiar patterns are no longer so familiar, and you have to be creative to see the same images presented that way. 

4. Uniquely southern objects 

Jewel Box Cluster

Although my experience was an urban one, I did see some special objects. Alpha Centauri itself is a good telescopic object, as it is actually a double star system and at the Sydney Observatory I had a nice view of this through a 14 inch telescope there. Also, the amazing Jewel Box Cluster is a great open cluster that is quite striking through binoculars or a telescope. 

The two things I would have liked to see were the Large and Small Magellanic Clouds, nearby dwarf galaxies that are large and impressive, but easily washed out in the light of the city and a full moon. That will have to wait for my next trip to Australia and for that one, I’ll plan a night out in the country to see the true depths of the southern Milky Way and the Magellanic Clouds. For now, I am extremely satisfied with the chance to have seen the overall change in perspective in the southern hemisphere, and of course the bright stars of Centaurus, the Southern Cross, and the Jewel Box Cluster.