Sunday, November 8, 2015

Light Pollution and Skyglow - Some Thoughts

Relaxing under a clear nighttime sky - with millions of twinkling little stars looking at us, is always a tranquil experience. Isn't it?

And bring to mind the grandness and greatness of the universe. Andromeda Galaxy, the nearest galaxy to ours, is around 2.5 million light years far. That means, what we see today is something from 2.5 million years back!! Long before even the first human on Earth!

But..

What is light pollution


By this time, you might have heard a lot about this. If you haven't, light pollution means hampering the natural darkness of the night due to wrongly directed artificial lights. It is often seen as a sky glow above populated areas and cities. Sometimes it looks like a glow in the horizon, making zenith darker than the horizon.


Light Pollution - Sky Glow

Light Pollution - Sky Glow

Notice the glow in the horizon. There is a town in that direction, miles away. Photos were taken from my backyard - just a small example to illustrate sky glow. 

Why does it matter


If you have ever watched the night sky from both a city and from a remote place/village, you know the difference. Not many stars can be viewed from a city, due to the sky glow. That hinders us from experiencing the serenity and peace under a pure night sky.

Light pollution is posing a challenge for astrophotographers and amateur astronomers as well. In fact, I began noticing this seriously when I went out to photograph the Milky Way. That's when I came to know how difficult it has become, to find a good spot for Astrophotography. On a clear Moonless night, the Milky Way should be clearly visible to the naked eyes. But that is not the case in many places, and the reason is sky glow. If the brightness of sky glow is greater than that of the Milky Way, it won't be visible.

Milky Way and Light Pollution

Sky Glow in the bottom right corner

It is also a threat to nocturnal living organisms. Health problems and sleep disorders add to it. Whether the light source is warm or cool is also important. From what I have learned, warm colors are less harmful than cool colors at night.

Solution...


Does that mean we have to stop using lights? No! Because light pollution is caused by light escaping into unwanted areas, mainly sky. So it is actually an energy wastage. So preventing that energy wastage is the solution to light pollution. For example, a street lamp is meant to illuminate the road/street. But if it is pointed (partly or completely) upwards to the sky, it doesn't illuminate the road efficiently and also causes sky glow - that is a waste of energy. So designing and installing the light sources in such a way that it light up only the required areas, is a solution for light pollution too.

Measure the sky quality yourself


You can measure the level of light pollution of the sky above you with a smartphone. Here is the concept behind it:

The brightness of celestial objects as seen from Earth is often represented in terms of Apparent Visual Magnitude. The logarithmic scale extends to both sides of the number scale and inversely related to brightness. That is, the higher the magnification, lower the brightness. 

The star Vega is considered to have nearly zero magnitude. Sun has -26.74, Venus has a maximum of -4.89, Andromeda around 3.5 etc.

Android users can use an app called Loss of the Night to measure the sky quality. The app guide you to locate different stars and asks whether it is visible to you or not. I have used it myself to measure the quality of my home sky. And I got the result around 4. The results may not be very accurate, but it gives an idea. The limiting magnitude (faintest star) for humans is around 6 (if the sky is free of light pollution).

Remember to choose a safe place and Moonless clear night to observe. 

iPhone users also have an application called Dark Sky Meter, but I haven't used it. You can visit International Dark Sky Association website to get more information.

You can also submit the results to Globe at Night website and participate in the citizen scientist program.

Feel free to share your thoughts on the topic...



1 comment:

  1. Same light I used to see when I was in my village with my Grand Parents and populated city far away always glowing and causing light pollution.

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