If you live in a city, light pollution is probably the number one obstacle to your astrophotography.
It likely means you won’t be able to just go into your garden and take Milky Way or deep sky images.
(The number two issue is that you often have to get up in the middle of the night to time your pictures perfectly!).
But what is light pollution and how can we get around it?
1. How does light pollution affect astrophotography?
To photograph the night sky well you need dark skies.
This is why if you want to photograph objects in the night sky, you should plan the day you will shoot to avoid a bright moon.
In the same way, but harder to avoid, you need to overcome the impact of light from urban areas glowing upwards and brightening the skies.
This is what light pollution is and is an effect of human development. It is particularly a problem if you leave in, or near, a city or town.
2. How to overcome light pollution for astrophotography
There are three ways that you can try to minimize the impact of light pollution on night photography:
- Travel to dark skies
- Use light pollution filters
- Lobby to reduce light pollution
We dig into each of these below.
3. Finding dark skies with light pollution maps
If you would like to find dark skies, there are some great online resources:
- This light pollution map by Dark Site Finder is a free resource that allows you to quickly see the best places in the world to find a dark night sky. The map images used below are taken from this website.
- Dark Sky Discovery offers a dark sky map service with details of stargazing events for those based in the UK. It’s a pretty interactive site; you can nominate local places that are good for astronomers.
- The International Dark Sky Association also has a world map showing the positions of locations designated as part of the International Dark Sky Places Program and is a useful resource although it isn’t a comprehensive map of general dark sites.
You may also find a light pollution smartphone app useful when out and about. Here are three of the best:
- SkyLive for those with iPhones has everything you need to plan your star observations. It takes weather, light pollution, and interesting astronomical events into account and much more.
- The Light Pollution Map by Photographer’s Arsenal is available across a range of platforms including Android and provides up-to-date information about light pollution, as well as many other features, such as lunar eclipse alerts and meteor showers. It’s free with an option to upgrade for a fee.
- The Loss of the Night app for the Android OS invites users to take part in a worldwide project that aims to help scientists quantify the problem of light pollution. The app basically works by guiding you to a certain star and asking you if you can see it. Educational and useful, this app gives a high level of user satisfaction and is well worth exploring.
Light pollution map of the USA
As you can see, the more sparsely populated areas of the Mid-West of America have much darker skies than the coastal areas and, in particular, the East Coast.
Light pollution map of the UK
The tightly populated islands of the UK and Ireland mean that truly dark skies are hard to find.
There are areas in Wales and Scotland in particular, but in general, you the farther you get from the big cities of London, Manchester, Liverpool, Birmingham, and Glasgow the better.
Light pollution map of Australia
The contrast between the UK and Australia maps is pretty stark, but Australia is a much, much larger place and with the vast majority of it unpopulated.
If you are around the big cities of Sydney, Melbourne, Brisbane etc, you can see that light pollution would be an issue for you.
4. Light pollution filters for astrophotography (and astronomy)
Light pollution filters are an essential piece of kit if you want to take clearly defined photos of astral objects in the sky or anything at night without the streetlights showing as a horrible glow.
There are many kinds of filter and, basically, their job is to reflect or absorb the wavelengths of light generated by artificial city lighting, while allowing the rest of the visible spectrum to get through to your lens and sensor. This results in a crisper image with much less blurred light.
You can buy different sizes and strength to fit on telescopes or for use with a DSLR camera – and prices to suit all budgets.
5. Lobbying to reduce light pollution in your area
This is where you get your House of Cards on and start influencing.
Honestly though, this may sound daunting and something that you wouldn’t want to do, but it may be as simple as writing to your local representatives to tell them that this is an issue that you care about.
There are really few downsides to turning unnecessary lights off at night – not only for the impact on light pollution but also to reduce energy usage and costs.
This doesn’t mean we all have to sit around in the dark, it’s about taking sensible steps to make light more efficient and less intrusive. We can do this by:
- Lobbying governmental bodies to put light pollution laws into place – these could fine companies who leave office lights on in tower blocks all night, for example;
- Adopting intelligent street lighting solutions that use wireless technology to be controlled from a central management system;
- Joining campaign groups, such as the Astronomical Association’s Campaign for Dark Skies and lobby for light pollution legislation.
There are also simple steps that we can all take:
- Installing reflectors in a garage driveway or garden path rather than a row of lights – and lobbying for the banning of ‘Rottweiler’ lights – 100-watt halogen lights that emit an ultra strong and completely unnecessary glare;
- Only using outdoor lighting when necessary. Lighting operated by motion sensors is a good solution;
- Swapping high wattage bulbs for dimmer ones.
Light pollution FAQs
1. What is light pollution and what are its causes?
Just over a hundred years ago, people in towns and cities could look up at the night skies and clearly observe the wonder of stars on a clear night. Now, millions of children across the world have never had the chance to see the wonders of the Milky Way.
This is because of light pollution.
Light pollution is defined as the unwanted presence of anthropogenic (caused by human activity) light in the night sky. It is an unwanted consequence of outdoor lighting and the increase in human population living in cities over the same length of time.
Different elements include:
- Glare – this is unrestricted brightness that hurts your eyes if you look at it for too long
- Skyglow – this term is used to describe the brightening of the night sky over urban areas and can be a mixture of natural and unnatural light sources
- Light trespass – this refers to light encroaching where it is not wanted or needed
- Clutter – a grouping of lights that collectively generate too much light
This is an inevitable side effect of industrial civilization. Common sources of light pollution include street lights, exterior and interior building lights, commercial offices and properties, and floodlit stadiums.
2. Why is it a problem?
The growing use of man-made light has serious environmental consequences for the natural world – humans, wildlife, and the climate.
It has profoundly negative consequences for nocturnal animals, such as badgers and foxes. Birds that hunt or migrate at night can become disoriented by artificial light. Every year, millions of birds needlessly lose their lives after crashing into tall unnecessarily illuminated office buildings. Countless other species are affected by light pollution, many in ways which we are only just discovering.
Humans are also affected by light pollution, which can have a negative impact on circadian rhythms and generally contributing to sleeping disorders, which can lead to many health-related issues.
Light pollution also affects the ability of astronomers and astrophotographers to observe and study the sky.
Unshielded lights send rays in all directions, including upwards. This makes astral bodies much harder to observe and photograph. Light pollution also plays havoc with spectroscopy, the study of spectra of an object and one of the most important tools for land-based astronomy.
3. When did it become a problem?
Light pollution is a fairly recent problem and was first observed in the early years of the twentieth century, around the time when towns and cities first adopted electric lighting.
However, the effects of early electric and gas lights were negligible compared to the visual assault caused by the sheer number and intensity of modern lights, particularly with the advent of inexpensive LED lighting, which resulted in more lights for less energy.
4. How is it measured?
Light pollution can be measured in several ways, for example, by:
- Taking measurements from the Earth’s surface to calculate night sky brightness;
- Taking aerial measurements to measure direct or reflected luminance;
- Taking measurements from outer space via the International Space Station or satellites.
The Bortle Scale measures Night Sky Brightness by using the limited magnitude of stars for comparison. It uses a scale of 1 to 9, with 9 being the worst.
The Sky Quality Index is another way of measuring Night Sky Brightness and uses a calibrated photometer to produce extremely accurate results.
As well as photometers, astronomical CCD and DSLR cameras are used to capture images of the entire night sky and create a luminance calibrated color map.