EARTH Hour is about to go beyond the Earth, with the International Space Station crew promising to turn off or dim non-essential lights on March 31.
Dutch astronaut Andre Kuipers will also provide live commentary from the space station, which orbits the Earth 15 times a day at altitudes of between 300 and 400 kilometres, as lights go off around the globe at 8.30pm local time.
Back on the planet, the event continues to expand, with Iraq, Bhutan and New Caledonia newly signing up to participate. About 1.3 billion people are expected to take part in the push to address climate change and promote sustainable use of resources.
''We have been getting enormous pick-up in the most unexpected places, like the Philippines, Malaysia, Brazil,'' said Dermot O'Gorman, the chief executive of event organiser WWF Australia.
''What we are seeing is citizens who are seeing environmental problems first-hand, and then seeing they can link in to be part of a global movement.''
So far, governments in 116 countries have said they will participate in Earth Hour this year, six years after the first event was held in Sydney. The total is still short of the 135 nations that joined in last year, but the organisers expect the number to surpass the 2011 event in the next two weeks.
To ''sign up'' for Earth Hour, a government body within a nation must agree to participate in the event, and to show its support by dimming lights on public buildings and monuments.
Mostly, this has happened because individuals wanted to participate and had asked government authorities why they were not joining in, WWF Australia said.
Among the well-known, and usually well-lit, buildings that will turn off their lights are the Eiffel Tower in Paris, Times Square and the Las Vegas strip in the US and Burj Khalifa in Dubai, the world's tallest skyscraper.
Some famous faces have aligned themselves with the cause, including former US vice-president Al Gore, cricketer Sachin Tendulkar and model Miranda Kerr.
In Australia, the number of businesses and groups committing to the event is growing.
''We've got about 2000 businesses, organisations and councils signed up so far, which is more than the same time last year,'' spokeswoman Marni Ryan said.
Earth Hour is supported by Fairfax Media, publisher of the Herald.