A Ring of Night

The original project

The idea to send a light signal around the Earth to mark the 50-th anniversary of Einstein's death (http://www.wyp2005.at/glob1-light.htm) is nothing bad, in principle.

Even if its simplest interpretation could be, that upon vast amounts of light which pollute the present night environment, the organisers propose to add just more of it, creating a wave of new lights spreading as a circle from Princeton.

The organisers claim that the amount of light may be insignificant in terms of further pollution, both by its amount and thanks to its short duration, and they are true. They don't specify the duration; I hope they will stress that it should be below one minute (even seconds may do), if it's not a huge 10-min firework as a tribute to Einstein.

Of course, all man-made light at outdoor night environment is pollution, and more light is more pollution. What are the options?

Let's think about light signals

All signals over large distances are transmitted either by sound or by light (within the reach of the arm, we can touch the neighbour to alert him, pebbles can be tossed further away, an arrow or a bullet is a signal which can be obtained from still larger distances).

In daytime, written texts, flags, balloons are common; smoke signals have been used ever since the humans mastered the fire; over shorter distances, gestures work excellently. Light signals can be seen over much longer distances when using telescopes to watch them. Even strong light flashes can be used, whenever you have a flat glossy surface by which you can reflect the sun rays.

At night, black smoke signals can be used against the bright horizon sky in many cases -- in fact, in all those, when the sky stands out as much brighter than the distant landscape. Of course, the fire itself can be much more conspicuous, when the sender and the observer have a direct visibility to each other. In a natural night environment, devoid of lights, any land-based star, even much fainter than the bright ones in the heavens, is easily detected. The signal can be made very directional, e.g. by having a fire inside a building, visible just through the door opened a bit for short moments (today's technologies offer much more directional lights).

Tiny amounts of light suffice for signalling at night. Stars midway between the bright and faint ones are conspicuous enough: and they illuminate your eyes no more than by 10^-7 lx. Seeing such a light point on a distant slope is enough to get a signal. With hand-held binoculars, ten times less light suffices very well. A yellow LED (or a candle, both have some 1 cd luminous intensity) can be easily seen over 10 km if the air is clean and you know very well where to look. At 1 km, you would immediately notice a candlelight even without a telescope -- as it is fully twice brighter than the Polar Star. For seeing light at 10 km so well, you need 100 cd (a bare 100W incandescent or a 20W CFL is surely enough, but a hand-held torch with a narrow beam can do the same job). For seeing an artificial landscape star at 100 km, at least 100 000 cd are needed, with very clean air (at least nine tenths of light are lost from the beam over such a distance; let's note that to see over 100 km over the curved Earth, both the sender and the observer have to be some 300 m over the landscape between them -- or just one of them at 1 km above the landscape). Narrow beam is needed to get enough luminous intensity: 200W incandescent collimated to 5 degrees with efficiency of 50 per cent should do.

In a strongly light-polluted environment, these luminous intensities still suffice, just the attention of the observer has to be devoted to the very point where the signal is to appear, and there should be no other, much stronger light points in the very same direction.

Signalling by light in the polluted night environment is complicated by the fact, that there are so many glaring lights everywhere around, which present no useful signal at all. Every sailor knows that: pilot lights have been strong enough over the last century (and modest at the same time, not spoiling the dark adaptation very much). But finding a decent pilot light at the entry to the port is not easy since the HID sources became common. Around a pilot light, there are often dozens of much stronger, non-signal lights, made in such a stupid way, that most of their output misses their proper target. Accidents, even casualties, due to people overlooking a pilot (traffic) light among another lights are a consequence, both on sea and inland waters, and many more on the roads. Signals are lost in the noise.

A tribute to Einstein

All common lights we see over large distances are a noise. Both the directly visible light points (bad luminaires) and the light domes over the lit areas. To send a signal, we have to get something what would be perceived even within this noise, something really ``loud''. Well, do we?

No, we don't. There is another option: reduce the noise.

The long-term goal should be to avoid light wherever and whenever it's possible. The International Dark Sky Association is on this track. But what about the April 18-19, 2005, could we achieve something before that?

Yes, we can. For sending a signal, we can reduce the noise in the selected direction at least, to make a tiny signalling light visible. It could mean, that one, three, or a dozen bad luminaires get a proper shielding, to become invisible and unpolluting when seen from a distance. One week of effort could do to accomplish that. Such a small, but nice step toward sustainability would be a good tribute to Einstein.

But there is another, much easier and cheaper possibility. Switching on some special light is one possibility to send a signal. For signalling, any modulation of light can be used. Switching off some light or lights, which would otherwise shine all the night through, is another possibility, even better apparent in the light-polluted environment! Instead of spreading a wave of some-more-light over the Earth, we can celebrate Einstein by sending a impulse of switched-off lights over the ever-lit urbanised landscape...

We celebrate memories of great people who just passed away by a minute of silence. Let's celebrate Einstein by at least a minute of absence of light noise. As a minimum, let's switch off the public lighting, and ask all private persons to do the same with their lights. Let's switch off the lights at homes and go outdoors, to enjoy the evening. Instead of a forced blackout, let's organise a short-timed voluntary one.

Such a signal could be visible over 100 km: a city light-dome is sometimes apparent so far away when observed from rural environment. Another city could follow when it sees that the villages in between, noticing the short return of true night sky in the first city's direction, switch their lights off in their turn.

Such a spectacle would be visible even from the universe: a ring of unpolluted night landscape spreading from Princeton...

Even if the minimum duration of the dark impulse is some two minutes only (for HPS lamps), any nation could prefer to let it last longer, say half an hour. Within that time, the eyes would adapt to dark and the true glory of the heavens would emerge.

Well, at the evening of the very anniversary, the starry heavens won't attain its full splendour. The waxing Moon, two days after the first quarter, will dominate the sky.

The advantage is there will be enough light (with clear skies, 0.03 lx at least) to be able to leave outdoor lighting off for a good while. Still, hundreds of stars would be visible, if the Moon would remain the only source of glare and skyglow.

If the sky would be overcast with no stars visible, it would be a good occasion for a decent firework. With no disturbing streetlamps anywhere, even modest effects would be impressive. Of course, a minute of silence and darkness before and after such a show would make the occasion a much better festival.

True Enlightment

Physics had damaged the world (by offering so much cheap outdoor light, not caring about its use) a lot already. Many children have never seen the Milky Way at all, not to speak about enjoying it with all its delicate dark nebulae and clear spots where wee see far through our Galaxy disk.

Enlightment of the mankind shouldn't be made by adding more light, but by enabling the people to witness the Lights of Nature once again. Milky Way will be scarcely visible low in the sky that evening, but at least the Big Dipper would stand out in zenith and even the Little Dipper would be easy to see, with its faint stars between Polaris and Kochab, which have disappeared in cities decades ago. It would be a good memory:
thanks to Einstein, I've seen the Little Dipper on my own eyes!

The enlightment could go further: letting the lights off all the rest of the night. It could be a night of good sleep (darkness is a necessity for it), contemplation, listening the sounds of night nature, admiring the heavens. Remembering the past Einstein's world and times.