Navigating By The Stars

On Monday night much of the inner north on Melbourne suffered a blackout that went on for around six hours. I had to ride from Brunswick to Preston and back and it was a very odd experience. While for the majority of the way houses, shops, street and even traffic lights were out there were patches that were lit up as if nothing was happening. For example crossing Sydney Road was nerveracking without traffic lights, but Lygon Street was fine (at least where I crossed) and even on Sydney Road there were blocks of 5-10 shops that still had power while those on either side were in darkness. Cudos btw to Jewell, which when I came back was serving dinner by candlelight benefiting from the fact they have a wood fired oven.

When my housemate got home we chatted about the experience and she commented how bright the stars were with the local lights out, even though the city centre was unaffected. I mentioned that I had got lost at one point on the return journey and, getting an ambiguous indication from the maps on my phone had navigated by the stars.

She was extraordinarily impressed with this, as if it was a sign of my great talents as an astronomer. Err no. I have a friend whose father was a navigator for the RAF during the second world war, and when the navigation equipment was shot out over Germany he won a medal for bringing the plane home navigating by the stars. Now that is impressive. In an urban environment where you know the streets are running largely east-west and north-south, and just need to know which is which, navigating by the stars is exceptionally easy, as long as they are out.

The Southern Cross looked magnificent Monday night without competition from city lights, but it is bright enough that, even under terrible light pollution conditions you can pretty much always see it if it is clear (and night time). For precision navigation you may wish to find the south celestial pole. There are several ways to do this. The most commonly used way is to draw a line from the “head” to the “foot” of the Southern Cross and keep going four and a half times this length. Since it is hard to estimate four and a half multiples of a celestial length without equipment some people prefer to look for the point where a line
drawn along the length of the cross would intersect a line using two other stars. Wikipedia
suggests a line bisecting the pointers, but in summer I tend to use a line from Sirius to Canopus, the two brightest stars in the sky.

Southern Cross, Pointers and Milky Way by Phil Hart.

However, when you only need very rough directions because the street layout largely guides your way, you don’t need to be able to find Canopus or even recognise the pointers. Just look for the Southern Cross. If you’re in the Southern Hemisphere and not in Antarctica it will be broadly to the south.

There are quite a few reasons why I run astronomy nights – to raise money for good causes, to catch up with friends, because I like talking about science. An additional reason is that I think it is sad how disconnected many urban dwellers have become from the skies. Living in the city means you don’t see the stars in their stunning glory, but that is no reason to neglect them entirely. I wonder how many of the people wearing southern cross tattoos could even find the southern cross in the sky.

Astronomy as a hobby has brought me a lot of pleasure over the years. Maybe it won’t be the same for you. But one of its great features is that it is something you don’t need to delve into too deeply to start finding value. There is no need to feel inadequate if you can’t recognise 88 IAU recognised constellations, let alone any of the Aboriginal ones or those from other cultures. I certainly can’t. But the Southern Cross, Orion and Scorpio are a very easy place to start. And you never know – one day when your phone isn’t working it might come in handy.

Note: The image above is by the exceptional Melbourne astrophotographer Phil Hart. I have had the pleasure of meeting Phil on a number of occassions and am hoping it is ok to use this image here. This and many of Phil’s other images are available as high resolution prints here.