Finding dark night skies was easy only two or three decades ago, but lately extravagant and excessive outdoor lighting has spoiled the skies over most of Europe. Light pollution is widespread and increasing rapidly, making it more and more difficult to find good skies to enjoy celestial phenomena like the upcoming Quadrantid meteor shower. Let us take a look at where we still can find good night skies.
The widespread expansion and proliferation of outdoor lighting has degraded the night skies to the extent, where few people actually ever get to experience truly dark night skies. Dark night skies have become rare, in fact several European countries have virtually no dark night skies anymore.
There is a common misconception, that light pollution extends about as far as you can see the actual lights, e.g. you only need to get out of direct sight of lights to escape light pollution. Unfortunately, this is not so. The sky is brightened dramatically by scattered light from lights out of direct sight. In fact, even poorly designed or applied lights can cause brightening of the sky overhead through scattering even tens of kilometers away. Light sources that emit light at low angles can cause light pollution over a hundred kilometers away.
Where to find dark skies?
Get as far away from urban centers as possible. If you can get some altitude as well, that will also help. Use the light pollution map below to find your observing spots.
Find the closest dark skies with Light Pollution Map.
So how good is your sky?
How do you know how good your sky actually is? The sky at your place looks good, you can maybe even see some Milky Way – there are ways to measure the sky brightness using specialized equipment from handheld sky brightness meters to measurements using CCD cameras. But there is another way of estimating how dark your sky is, without the use of any equipment. Veteran astronomer John Bortle, an amateur astronomer with over six decades of experience, has formed the Bortle dark sky scale. It ranks the night sky by the visibility of the Milky way and other celestial objects and the extent of light pollution [slightly edited]:
Summer Milky Way under a Bortle Class 2 sky in Crestone, Colorado. Note the green natural airglow. Photo: Jure Atanackov.
- Class 1 – Excellent dark-sky site: the zodiacal light, Gegenschein, and zodiacal band are all visible — the zodiacal light to a striking degree, and the zodiacal band spanning the entire sky. The Scorpius and Sagittarius region of the Milky Way casts obvious diffuse shadows on the ground. The presence of Jupiter or Venus in the sky seems to degrade dark adaptation. Airglow (a very faint, naturally occurring glow most evident within about 15° of the horizon) is readily apparent. If you are observing on a grass-covered field bordered by trees, your telescope, companions, and vehicle are almost totally invisible. This is an observer’s Nirvana!
- Class 2 – Typical truly dark site: airglow may be weakly apparent along the horizon. M33 is rather easily seen with direct vision. The summer Milky Way is highly structured to the unaided eye, and its brightest parts look like veined marble when viewed with ordinary binoculars. The zodiacal light is still bright enough to cast weak shadows just before dawn and after dusk, and its color can be seen as distinctly yellowish when compared with the blue-white of the Milky Way. Any clouds in the sky are visible only as dark holes or voids in the starry background. You can see your telescope and surroundings only vaguely, except where they project against the sky.
- Class 3 – Rural sky: some indication of light pollution is evident along the horizon. Clouds may appear faintly illuminated in the brightest parts of the sky near the horizon but are dark overhead. The Milky Way still appears complex. The zodiacal light is striking in spring and autumn (when it extends 60° above the horizon after dusk and before dawn) and its color is at least weakly indicated.
- Class 4 – Rural/suburban transition: fairly obvious light-pollution domes are apparent over population centers in several directions. The zodiacal light is clearly evident but doesn’t even extend halfway to the zenith at the beginning or end of twilight. The Milky Way well above the horizon is still impressive but lacks all but the most obvious structure.
- Class 5 – Suburban sky: only hints of the zodiacal light are seen on the best spring and autumn nights. The Milky Way is very weak or invisible near the horizon and looks rather washed out overhead. Light sources are evident in most if not all directions. Over most or all of the sky, clouds are quite noticeably brighter than the sky itself.
- Class 6 – Bright suburban sky: no trace of the zodiacal light can be seen, even on the best nights. Any indications of the Milky Way are apparent only toward the zenith. The sky within 35° of the horizon glows grayish white. Clouds anywhere in the sky appear fairly bright.
- Class 7 – Suburban/urban transition: the entire sky background has a vague, grayish white hue. Strong light sources are evident in all directions. The Milky Way is totally invisible or nearly so. Clouds are brilliantly lit.
- Class 8 – City sky: the sky glows whitish gray or orangish, and you can read newspaper headlines without difficulty. Some of the stars making up the familiar constellation patterns are difficult to see or are absent entirely.
- Class 9 – Inner city sky: the entire sky is brightly lit, even at the zenith. Many stars making up familiar constellation figures are invisible, and dim constellations such as Cancer and Pisces are not seen at all.
Autumn morning Zodiacal light in a Bortle class 3 sky in western Slovenia. Photo: Jure Atanackov.
Light pollution is a much bigger problem than ‘just’ destroyed night skies!
Light pollution is a much larger problem than ‘just’ the loss of naturally dark night skies. It has important effects and consequences also in health, traffic safety, biodiversity and energy consumption. More on this soon.