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Skywatching

Light pollution is the bane of stargazers

Searching for dark skies

The old Royal Greenwich Observatory sits at the top of a hill on the south bank of the Thames, downstream from the centre of London.

Founded in the 17th Century it was set up to improve navigation at sea. The line of zero degrees longitude passes through it. At the time it was built. Greenwich was far out in the country. Then, the telescopes were driven away by the increasing light pollution from a rapidly expanding London to a new location at Herstmonceux, Sussex.

The old building became a museum. The Isaac Newton Telescope, with a 2.4 metre diameter mirror was built at the new site, but the growing light pollution eventually led to the telescope being moved to the Canary Islands, where the skies still dark.

The Dominion Observatory sits close to Carling Avenue in south Ottawa. It was founded in 1902 primarily for time-keeping and navigation. The light pollution from an expanding Ottawa area led to the observatory closing in 1970. In a familiar vein, the David Dunlap Observatory, near Toronto, operated as a front-line research facility from 1935 to 2007, at which point it was closed. Fortunately though it has reopened to provide an opportunity for the public to look at the sky through a large telescope.

Then there is the Plaskett Telescope, with a 1.83 metre mirror, located on a mountain in Saanich, on Vancouver Island, not far from Victoria. It opened just after the First World War. Once again, its value has been degraded by light pollution. Fortunately, it is still doing science and also is used for public observations.

The common thread in all these stories, and many others for which there is not enough space, is that of growing light pollution, which makes it harder to find good sites for telescopes.

The same story applies to radio telescopes. Finding accessible locations remote from our growing cacophony of radio interference is a big issue.

There is another thing—it is usually affordable to locate major astronomical instruments at good sites and these days, to some extent at least, regulate light pollution and radio interference produced around them.

These powers are not available to smaller organizations operating telescopes for research and public use, and even less for the millions of back-yard sky watchers around the world. Light pollution has reached a point where many people have never seen the Milky Way, or anything other than the Moon and the brightest stars and planets.

The cause is most easily seen from space. Images of the night side of Earth taken from the International Space Station show great patches of light marking cities, connected by glowing ribbons of roads.

Western Europe is almost completely lit up and it is easy to see the population distribution in North America. What we are seeing is millions, or billions, of watts of energy being used to pointlessly send light into space.

When we light streets, sending a good fraction of the light in directions other than onto roads, it is wasted energy. How many streetlights are there? Backyard lighting is often needed for security reasons. Lighting up your neighbour's backyard means that in addition to annoying your neighbour, you are wasting money. These days we have the technology to save a colossal amount of energy and avoid dumping into the atmosphere the carbon dioxide we produced generating it.

Getting from my home into town involves driving down a winding hill. The last few hundred metres of road have been equipped with extremely efficient LED streetlights, which send almost all their light down onto the road. All we see from above are illuminated road surfaces.

We have the technology to save money, reduce carbon dioxide production and make it possible to sit in our yards on a summer evening, enjoying the stars.

•••

• After sunset, Venus lies low in the sunset glow, with Jupiter and Saturn low in the south.

• Mercury is low in the predawn sky.

• The Moon will reach its last quarter on Oct. 28.



More Skywatching articles

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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