Useful Article: Urban Astronomy - Seeing the Skies in Light Polluted Areas
- Filed under: Astronomy
- Date: Oct 17,2008
Urban Astronomy - Seeing the Skies in Light Polluted Areas
The sheer, overwhelming amount of light pollution from a city can lead many of its inhabitants to believe that there is no way they can view anything from urban areas. Its not just residents who feel this way, I’ve even talked expert astronomy authors who have told me that there was no reason to get a telescope larger than 3″ diameter for city use as the light pollution would make that extra aperture useless.
The real truth of the matter is a bit different: While city astronomical viewing is hardly ideal, it is far and away from the futile effort that many ‘experts’ would have you believe. In fact, there are a few tricks you can do that may actually give you a decent viewing experience:
Look Up!
Its a sad fact of life in the city: People rarely actually look up! And when they do, it is usually to admire some brightly lit building. But if you get in the habit of looking up in the sky at night you will start to notice that on clear nights there are objects in the sky that can be seen, and there’s more than just the Moon up in the sky! Getting into this habit will also let you spot the ideal nights for viewing. Of course, make certain you are not looking up at a tall building or street light first!
Get Away from the City Center
The center area of any city is where its light are brightest and its building are tallest. Getting just a mile or two, or even just a few blocks away from brightest buildings can result in some surprisingly excellent views of the night sky. I myself have been able to naked-eye view the Orion Nebula (with averted vision) from both the Ferry Docks in Manhattan, as well as in Northeast Philadelphia!
Get High!
The vast majority of light pollution in a city comes from its street lights. The trend in cities is to add more street lamps instead of removing them, so don’t expect them to go away anytime soon. But the good news is that most of street lights’ light is pointing down (and sadly, being reflected back up, but that’s another story). If you can get above these lights (which usually reach the third floor in most cities) by going on roof of a tall house or deck high above the ground you will avoid a large portion of the light pollution the city produces. Decks and roofs are not ideal for astronomy. Most decks are wood and prone to bouncing when you walk on them, your telescope image will shake accordingly if someone is moving around on your deck. In addition, not all roof decks have access that is easy to bring a telescope up to. Your mileage may vary.
Pick Your Nights Wisely
If you want a chance to see more than just the Moon and Planets, you will need to be choosy about which nights you want to do city observing. In addition to clouds, haze is a frequent factor in the night skies over cities in the warmer months and will spoil most viewing. The best nights for viewing will probably be in the Fall/Winter months.
Adapt your Eyes!
Amateur astronomers write volumes on getting their eyes to adapt to nighttime so that they can get the most out of their telescope viewing. They are, of course, assuming that you are working with excellent dark skies far away from any light pollution, but don’t let that fact put you off letting your eyes adapt. All too many urban astronomers walk out of their lit buildings and glance immediately up into the sky, without allowing their eyes any night adaptation whatsoever. This is not a good way to assess the night sky; instead give your eyes a few minutes to adapt to conditions. To do this avoid looking at any lights. You can sit in a chair and look up at the sky and you can actually see the effects: More and more stars will seem to ‘appear’. Its not that the city sky is improving, its just your eyes adapting to the night.
Choose Your Targets Wisely
Even with all these hints, you should be be judicious in what you want to view in the urban night sky. Trying to view Magnitiude 15-20 (the higher the magnitude, the fainter the object) objects is a daunting task even in the darkest skies and so should probably be avoided. Targets you should consider instead would be:
The Moon: The moon is utterly unaffected by light pollution. In fact, even in the city you might consider using a Moon Filter as the light can be quite bright through a telescope. Keep in mind that the best time to view the Moon is when it is waxing or waning, not when it is full. Why? Because when the Moon is full the light is shining right down of the surface and so you get few shadows to show you details.
The Planets: Jupiter, Saturn, Mars and Venus are also little affected by light pollution. You can enjoy the rings of Saturn as well the moons & bands of Jupiter with any decent telescope. Venus and Mars can also be enjoyed, however the former is very bright and shows only its crescent shape, wheras viewing the latter is often dependent on how close it is to Earth.
Brighter Deep Sky Objects: You won’t get magnificent images of nebulea and galaxies, but you still enjoy them with a decent telescope. The Orion Nebula is one of the easiest objects to find in the night sky, while the Andromeda Galaxy can it least be partially seen on clear nights from the city. Make certain you have a decent star chart or Planisphere to pick your viewing targets.
In Conclusion
Urban astronomy will never match finding true dark skies far out in the country, but don’t let naysayers tell you that you “Can’t see anything in the city”. You most certainly can!
About the author
Matt Kriebel is the owner of the telescope & science store Spectrum Scientifics. Spectrum Scientifics is your source for telescopes, microscopes, binoculars, science toys, weather instruments, robots, and much, much more.
Spectrum Scientifics: Telescopes, Science Toys, and Science Fun! www.spectrum-scientifics.com.
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