Dark skies

Ken Tapping, August 28 2013

In the sky this week…

  • Venus and Saturn lie low in the west after sunset.
  • Jupiter rises about 2 a.m. and Mars about 3 a.m.
  • The Moon will reach Last Quarter on the 28th.

If you have ever been out in the wilderness, far from city lights, you will remember what those night skies looked like. There were so many stars it was hard to pick out familiar constellations, there was a manmade satellite crossing the sky every few minutes, and the Milky Way was amazing. You will have noticed that with your fully dark-adapted eyes, the sky looked dark grey rather than black, and your view had a rather grainy look, indicating it was dark enough for your eyes to work at the limit of their sensitivity, which does not happen often. With the exception of artificial satellites, that must be how our ancestors saw the night sky. This must have encouraged them to arrange the stars into constellations and to put their mythology in the sky. Almost all the world’s civilizations did this.

Sadly, the almost spiritual experience of enjoying a truly clear, dark, night sky is getting more difficult. The problem is us. The way we light our cities is incredibly wasteful of energy, because we happily generate light and send it upwards, where it lights nothing useful. It gives photographs of the Earth a sad beauty. The wasted light scatters off haze and dust in the atmosphere, making the sky glow and obliterating all but the brightest stars. There is a growing consciousness among communities in the western world that we can enjoy darker skies while saving money, through intelligent use of light. However, that will never yield the crystalline darkness we get by being far from streetlights.

Professional astronomers solve this problem by carefully sitting instruments on remote sites or the tops of mountains, using the clouds below to block out the lights. Unfortunately, amateur astronomers and those who just want to enjoy the sky do not have access to such locations. The more dedicated will drive for hours to get well away from cities and the housing developments expanding out from them. Many of those with families and modern career pressures may not have the time to do this. A more easily accessible option is needed.

Today, our searches for planets orbiting other stars suggest all stars have planets. If we assume just three planets per star on average, then there are 90 billion planets out there orbiting Sun-like stars. If we believe our Solar System is typical, there could be almost 10 billion Earth-like planets in the Milky Way, suitable for life as we know it.

A solution being implemented in Canada and some other countries is to set up “Dark Sky Reserves”. The idea is to pick really good, dark locations that are not too far from the communities who will enjoy them, and set up planning regulations that prevent the encroachment of street and other lights. The idea is to search out good, dark locations and then preserve them.

In many countries, high population densities can make it impossible. For example, in Britain today there are few truly dark locations. In Canada we are a lot better off. There is a lot of country and the population is small. Even with most of us living close to the US border it is possible to find nearby dark locations that can be preserved. There are dark sky reserves scattered across Canada, even in the relatively highly-populated areas in Ontario, not far from Toronto. Further from population centres it is easier to set up dark sky reserves and to make them larger. A dramatic example is the Wood Buffalo National Park, which stretches between Northern Alberta and the North-West Territories. On 2 August it was declared a Dark Sky Reserve. This reserve is bigger than Switzerland, and the second largest in the world. The biggest is in Greenland.

However, for many of us, enjoying the night sky takes place in our backyards or within a few kilometres of home. Fortunately, innovations in lighting technology and economic considerations are leading to better ways to put light where we want it, not squirting it in all directions.

If you are one of the few who have never tried it, there is nothing quite like lying in a sleeping bag, looking up at a truly clear, dark sky – mosquitoes permitting of course.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

Telephone: 250-497-2300
Fax: 250-497-2355

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