Have you ever thought about the importance of darkness?
We often take it for granted, but the night plays a vital role in our world. International Dark Sky Week 2025 is from 21st to 28th April, and on the blog this month we cover an important question: have you ever thought about the importance of darkness?
Dark skies are relevant to everyone, and Dark Sky Week promotes responsible lighting for protecting wildlife and ecosystems, human health, and the cultural heritage of the night sky.
National Dark Sky Week started in 2003 to raise awareness about light pollution and its impact on our night sky. With an early focus on encouraging people to turn off unnecessary lights to experience.
In the more than two decades since, it’s evolved from a simple call to observe the stars to a campaign to protect the night sky and mitigate the harmful effects of light pollution.
Growing global awareness of light pollution and its effects has helped broaden the event’s focus, expanding it to an international level. International Dark Sky Week is about more than just appreciating the night sky.
International Dark Sky Week tackles wildlife and ecosystems, human health, energy use and climate change, and promotes responsible lighting.
Why you should care about International Dark Sky Week
Light pollution negatively impacts wildlife
For billions of years, life on Earth has evolved under the predictable rhythm of day and night. Artificial light at night disrupts their natural behaviours, circadian rhythms, and predator-prey relationships.
For some animals, artificial light extends their perceived day length, while for others, it shortens it. This confusion causes mistimed activities, including foraging, breeding, and migration.
The recovery of threatened species is threatened by artificial light at night. Sea turtle hatchlings are guided by their instinct to move towards the brightest horizon, which would normally be the ocean. Artificial lights can draw them away from the ocean, and even those that make it to the ocean can be misdirected back towards shore.
How does artificial light at night affect your health?
International Dark Sky Week Darkness highlights the importance of darkness for our own health.
Chris Peterson, engagement manager for International Dark Sky Week says “over the past 100 years, humans have transformed the night, erasing the natural darkness with which we evolved.”
Darkness is essential for maintaining healthy circadian rhythms. These natural biological rhythms regulate various bodily functions, including hormone release, body temperature, and even cell repair.
Artificial light at night, even dim light, messes with melatonin production, making it harder to fall asleep and impacting sleep quality. Melatonin also has other important functions, including regulating blood pressure and body temperature.
Light Pollution Makes it Harder to See the Stars
A recent study, based on data from the Globe at Night community science project, shows light pollution is increasing by 10% every year. This is an exponential increase, meaning that the light pollution is 110% of the previous year’s level.
Astronomers measure light pollution with a simple scale called the Bortle Scale. Amateur astronomer John Bortle designed the scale for anyone to use and understand easily, regardless of equipment. Using visible objects as a yardstick for brightness, the Bortle scale measures how bright the night sky is in a location.
At the top end of the scale is Bortle 8/9, which is the sky in a major city like Perth. The entire sky is lit and only the very brightest objects, like planets, the Moon, and some bright stars, are visible.
In the middle of the scale, at Bortle 5, you have a suburban sky. You’re away from the CBD, but while you can see the Milky Way and the Magellanic Clouds overhead, you can see light pollution in most directions.
Astro Tourism towns typically provide typical truly dark sky sites Bortle 2 on the scale. According to skyandtelescope.org,, the Milky Way is highly structured to the unaided eye, and its brightest parts look like veined marble when viewed with ordinary binoculars.
Bortle 1 is an excellent dark sky site, and the darkest sky possible. At this end of the scale, the vast number of stars you can see in the night sky makes recognising familiar constellations harder.
Go outside this International Dark Sky Week and look at the sky. What can you see? Where does your location fit on the Bortle scale? You can report this data to Globe At Night and help them track dark skies.
What can you do to help?
Start with checking how you can improve your home’s lighting: read the Australasian DarkSky Alliance guide to Best Practice Lighting Principles for more info.
Here are a few other quick tips for tackling light pollution.
- Start with darkness: ask if you really need a light. Only add light if it has a specific purpose, and limit it to a location and set time.
- Turn off lights when you leave the room, and turn them out when you leave the house or office.
- Use curtains, shutters and blinds at night to keep light indoors.
- Shield outdoor lighting: flat lights or shielded lights direct light to the ground, not up into the sky.
- Warm-coloured light is better than white or blue light. Better for our sleep cycles, native animals, and reducing light pollution. For humans, orange is a better light colour than red for seeing in the dark.
You can make a difference tackling artificial light at night
Join the Australasian Dark Sky Alliance’s campaign to ask local councils to show they care about the environment, day and night, and take the International Dark Sky Week pledge to protect the night here.
Jay Chesters
Jay Chesters is a wordsmith with a little bit of a thing for the stars. As a cosmic storyteller with a love for astronomy and space that's out of this world, Jay’s always eager to share his knowledge and passions.
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