A Stargazers Guide-ish to the bortle scale
I took this three second image on my phone when I visited Perthshire near Meikleour Estates. Yeah, I know it's not an APOD winning image, but the skies were absolutely incredible. The only time I experienced close to Bortle 1 skies!
Stargazing is more than just looking up at the sky—it’s about experiencing the vastness of our universe, and connecting with something far beyond our daily lives. Whether you're a seasoned astrophotographer or someone who's just discovered the delights of the night sky, there's one challenge we all face, besides clouds, that is.
This is a simple but effective way to understand how light pollution affects what we can see when we look to our skies and beyond.
In this guide, I'll break down what the Bortle scale is, how light pollution impacts stargazing, and where you can find the best dark skies in the UK and beyond. Let’s do this!
So, what is the Bortle Scale?
The Bortle scale is essentially a tool that helps stargazers rate the quality of the night sky based on the amount of light pollution that is present. Created by astronomer John E. Bortle, it uses a simple scale from 1 to 9 —1 being the darkest skies you can find here on Earth, and 9 being the most light-polluted areas, where only the brightest stars can cut through the artificial glow caused by street lamps and other artificial lighting in areas. In Bortle 9 skies it is, at most, a tea towel of the most recognised asterisms or constellations.
Here’s a quick explanation:
Bortle Class 1 (Perfectly Dark Skies): The Holy Grail for astrophotographers and stargazers. Absolutely no light pollution. The Milky Way glows bright, and even faint celestial objects are visible to the naked eye; Andromeda galaxy, Orion Nebula and maybe Bodes Galaxy to name a few.
Bortle Class 2 (Near Perfect): Still incredibly dark, though you might notice a faint glow from distant towns. Excellent for observing deep-sky objects.
Bortle Class 3 (Rural Sky): You’re starting to see a bit of light pollution, but the Milky Way is still clear, and plenty of stars are visible.
Bortle Class 4 (Rural/Suburban Transition - where I live): Some light pollution is more noticeable, and the Milky Way fades ever so slightly but with a little more patience Orion Nebula is still visible to the naked eye.
Bortle Class 5 (Suburban Sky): This is where light pollution begins to hinder stargazing—fewer stars are visible, and the Milky Way becomes harder to spot.
Bortle Class 6 (Bright Suburban Sky): Only the brightest stars are visible now, and light domes from nearby towns or cities are obvious.
Bortle Class 7 (Urban Sky): Stars are few and far between. The night sky has a noticeable glow from streetlights, buildings, and other urban sources.
Bortle Class 8 (City Sky): The stars have nearly almost all but disappeared, and only the brightest constelations can now be seen.
Bortle Class 9 (Inner-City Sky): The sky is completely overrun by artificial light. It’s difficult to see anything beyond the Moon, a planet or two, and maybe the odd star.
How Light Pollution Affects Stargazing
Light pollution is the bane of stargazer's and astrophotographer's lives. It’s caused by the overuse of artificial light—streetlights, cars, billboards, and even the glow from our homes. This light scatters in the atmosphere, washing out the natural night sky and making it hard to see any or most celestial objects, especially fainter ones like distant galaxies or nebulae.
Light pollution can mean the difference between seeing a 'sky full of stars' or just a handful of the brightest ones. A teatowel of the most obvious constellations at most!
If you’re an astrophotographer, it can ruin your images by washing out the finer details and reducing the contrast between stars and the surrounding space. But in saying this, more modern light polution filters will help mitigate most of the ligh pollution these days. I used to use light pollution filters available from Optolong as an example.
Stargazing in the UK: The best places to look up
If you’re based in the UK, you’re probably already aware that light pollution can be a huge challenge—especially in urban areas like Glasgow, Edinburgh, London, Birmingham, or Manchester. In these city environments (which tend to fall into Bortle Class 7-9), your view of the night sky will be massively impaired and the Milky Way will be nearly impossible to spot. But don’t worry—there are still plenty of incredible places to enjoy the stars across the UK!
Here are some of the top dark-sky locations in the UK where light pollution is at a minimal. Some of these I have visited, some I have not. Maybe one day I can get to the Atacama!
There are some amazing Dark Sky reserves in and around Scotland and the rest of the UK. I have been to one near Dalmellington which used to have The Scottish Dark Sky Observatory (which sadly was raized to the ground by vandals a few years ago), and there is a fantastic dark sky area near Perth In Scotland and I swear I couldn't even visually navigate my around the night sky, there were so many stars visible. There are amazing dark skies in and around Galloway Forest in Newton Stewart and the further up towards the North of Scotland, the darker it gets.
Here is a dark sky map from the website Go Stargazing
Exmoor National Park (Bortle Class 3): One of the UK’s first Dark Sky Reserves, Exmoor offers stunning views of the Milky Way and plenty of deep-sky objects. It’s perfect for a weekend escape away from those pesky city lights.
Northumberland National Park (Bortle Class 2)**: If you’re looking for some of the darkest skies in the UK, Northumberland is the place to be. The park is part of Europe’s largest Dark Sky Park, making it ideal for astrophotography and deep-sky observation.
The Lake District (Bortle Class 3): A Dark Sky area known for its low light pollution and incredible views of the Milky Way on a clear night.
These locations are perfect for anyone in the UK who wants to experience the true beauty of the night sky without the disturbance of light pollution.
Going Further Afield?
If you’re feeling adventurous and want to take your stargazing to the next level, there are some truly breathtaking locations around the world where light pollution is virtually non-existent. I haven't been to any of these, but I know people who have. Jealous!
Atacama Desert, Chile (Bortle Class 1): With some of the clearest and darkest skies on the planet, the Atacama Desert is a haven for astronomers and astrophotographers. The Milky Way here is so vivid, it feels like you can reach out and touch it.
Mauna Kea, Hawaii (Bortle Class 1): At over 13,000 feet above sea level, Mauna Kea offers an extraordinary view of the stars, galaxies, and nebulae, with almost no light pollution at all.
Namib Desert, Namibia (Bortle Class 1): Another world-class stargazing destination which boasts pristine skies and a remarkable view of the Milky Way.
Jasper National Park, Canada (Bortle Class 2): Designated as a Dark Sky Reserve, Jasper is perfect for those wanting to experience the full glory of the Northern Hemisphere’s night sky.
Fighting Light Pollution:
While light pollution might seem inevitable, there are steps we can take to help to reduce its impact. Many cities and towns are adopting dark-sky-friendly lighting, which minimizes unnecessary light by using shielded fixtures and directing light where it’s needed, and I think my local council have adopted at least a bit of this. You can also make a difference by reducing outdoor lighting at home and supporting efforts to limit light pollution in your community. Take note, my good neighbour.
For stargazers and astrophotographers, the simplest, but perhaps not the easiest solution, is to travel to a dark-sky location whenever possible. If you can’t escape the city lights, using light pollution filters with your telescope or camera can help cut through some of the artificial glow and improve your viewing experience. Some of the light pollution filters have enabled some of these amazing astronomers and astrophotographers to grab some of these amazing deep sky objects using their telescopes and cameras.
By choosing the right location—whether in Scotland or the UK or somewhere further afield—you can maximise your chances of seeing the night sky in all of its beauty and glory.
Clear skies and happy stargazing!
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