Introducing the Shitty Sky Index™ [Astronomy]

WARNING: This is not about medicine. It is at least somewhat IT/data related though!

I’m an amateur astronomer. I like to take photos of things up in the night sky. It makes me feel totally insignificant as well as being something pretty to look at.

M42 - Orion Nebula - Compiled rough.jpg
M42 – The Orion Nebula. A picture wot I dun and took.

The problem with the UK is that it’s a pretty crap location for Astronomy. There are three leading reasons for this:

1) Cloud cover:
Our Cloud Fraction in the UK ranges from 65% in the summer to 90% in the winter. This is a measure of how thick the clouds are overhead on average. Clouds block out light. If you want to take photos of dim objects like nebulae, you need skies with almost no cloud.

Go on, take a look at how miserable the average weather is in your location.

2) Light pollution:
We are habitually throwing loads of light into the night sky. Most of this comes from poorly designed street lamps, but homes, cars and fires all contribute too. The UK’s high population density and general habit of living in scattered towns means lots of our land is glowing with our lights.

Things are getting better as more neighbourhoods install smart LED lighting which is designed to illuminate downwards only, can automatically dim at certain hours, and can brighten only when someone is walking near.

Paradoxically, those horrible orange sodium discharge street lamps of the 20th Century are possible to filter out using specially designed telescope filters, but they are only part of the total pollution. People who image using narrowband filters can punch through light pollution to some extent, but it still hits the contrast of the images.

When I want to look at dim objects from across the galaxy, or indeed at other galaxies, I need a night sky free from sky glow to stand a chance of seeing them, let alone photographing them.

3) Atmospheric Turbulence:
If you have ever looked out a window which had a hot radiator in front of it, you’ll have seen the visible distortion caused by currents of air. The same thing applies to our atmosphere. If the air is turbulent (windy high up) or there are warm fronts of air clashing with cold ones, we get visual distortion. This is what makes stars appear to jiggle about which is what we see as twinkling with the naked eye.

The UK is sat right on the edge of an ocean, with a warming beam of water (the Gulf Stream) keeping things mild at ground level (and cloudy, and wet), while the jet stream meanders overhead dragging in cooler air from the North Atlantic. Put the two together, and you’ve got the perfect mashup of temperatures to jiggle the ever loving crap out of the atmosphere.

When I take photos of dim things, I need to do long exposures (usually 5 seconds – 10 minutes). Jiggling atmospheric distortion blurs and buggers the image sharpness up.

It amazes me how Astronomy is a multi-million pound annual market in the UK despite this.

So, where might one find a suitable location for Astronomy?…

The Shitty Sky Index

Seeing as though we’ve had 14 cloudy nights in a row, I’ve been stuck indoors. So I decided to do some number crunching. I started with some public data sources:

These data sources show satellite captured measurements of cloud cover (averaged across a month), and night time light pollution (averaged across 10 years).

I created a composite map of the Cloud Fraction plus the Light Pollution using Google Earth. I then adjusted the overlay transparency to give a reasonable blend of the cloud cover versus the light pollution.

The result is a 2D colour-scaled map of how crap the skies are in locations across the world.


Dark blue locations rarely have any clouds. Whiter colours mean lots of thick cloud. The redder the colour, the more light pollution, the bluer the colour, the less light pollution.

> High res images on Flickr
BrooksShittySkyIndex - W Europe
Western Europe – Cloudy and swamped in light pollution.  Look at Belgium… Are they trying to pretend there’s no wider universe or something?

Rest of Europe:

BrooksShittySkyIndex - CW Europe.jpg
Rest of Europe – Someone has just barfed right across central Europe, then tried to hide the evidence with layers of clouds.

Middle East:

BrooksShittySkyIndex - Middle East.jpg
Middle East – Nothing keeps the clouds away like a scorched desert miles from the sea. It also keeps humans away by the looks of things. Israel & Palestine seem to overindulge in light however.

North, East & West Africa:

BrooksShittySkyIndex - N Africa.jpg
North, East & West Africa – Cloudless skies until you reach the tropics & Congo basin. The coasts of Nigeria and Gabon are alight with oil industry activity.

Southern Africa:

BrooksShittySkyIndex - S Africa.jpg
Southern Africa – JoBurg is a photonic mess. Namibia and the Kalahari region of South Africa are incredibly cloud-free. The Congo Basin rainforest makes its own cloudy weather.

South & Central Asia:

BrooksShittySkyIndex - S Asia India
Southern & Central Asia – A light belt rages from Islamabad down to New Delhi. Bangladesh, Thailand and Singapore all fond of lights too. Singapore is the most light polluted country on Earth, but that’s because the whole country is a city. South Pakistan, West India, and Chinese Tibet are very cloud free.

East Asia:

BrooksShittySkyIndex - E Asia
East Asia – Hong Kong, Shanghai, Beijing are all hot centres of light pollution. Chongqing seems to be a cloud magnet. Japan is carpeted in artificial lights. Note the stark contrast in light pollution between the hermit kingdom (North Korea), and South Korea.


BrooksShittySkyIndex - Oceana.jpg
Oceania – If you drive 400 miles out of Perth, you’ll find some proper dark and cloud-free skies. Plus kangaroos. The middle of Queensland is also nice and dark and fairly cloudless. The darkest sky I’ve ever seen was in the Atherton Tablelands there.

North America:

BrooksShittySkyIndex - N America
North America – Eastern USA is a light-polluted mess, much like Europe, except for the East strip of West Virginia*. California is bright along its coast. Colorado has some good spots outside of Denver. Spot Houston and Phoenix, I bet you can’t! For some reason there’s no light pollution data for North Canada.

* Interestingly, this region is in the United States National Radio Quiet Zone where radio transmissions are strictly limited to permit radio astronomy. The area houses the Green Bank radio telescope, plus military radio listening posts. Low light pollution, low-to-moderate cloud cover and decent elevation (2500-3000m) make the East half of West Virginia the best spot in Eastern USA for Astronomy.

Central America & Caribbean:

BrooksShittySkyIndex - C America
Central America & Caribbean – Mexico has mostly clear skies, spoilt by the huge splodge of central light glow in Mexico City. Maracaibo, Venezuela is pretty light polluted. What’s not shown is the Catatumbo lightning which rages for 180 nights a year just South of there. That’s natural though, and really rather cool.

South America:

BrooksShittySkyIndex - S America
South America – Once again the rainforest effect means everything above the Amazon is cloudy. The Andies form a weather barrier ridge, making Chile’s skies supremely clear. Unsurprisingly, high up on the Chilean Andes is exactly where you’ll find the European Southern Observatory.

So, in summary, if you had the freedom to choose where to build an observatory go for:

  1. Chilean Andes (the mountains get you above much of the atmosphere anyway)
  2. Tibet plateau (4500m up, again above much of the atmospheric soup
  3. Kalahari Desert (Namibia / W South Africa)
  4. 500km North of Perth, Australia
  5. West India (NW Gujarat region)

And places where you’ll be fighting both clouds and light pollution:

  1. Brussels, Belgium
  2. Stockholm, Sweden
  3. Singapore
  4. Glasgow, Scotland
  5. London, England
  6. Boston, USA
  7. New York, USA

When I next get the chance, I’ll do a proper recalculated KML file combining some weighted amount of the Cloud Fraction and Light Pollution.

> View high resultion images on Flickr


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