Rainbows form when sunlight is refracted (bent) and reflected by raindrops: Blue light refracts at a greater angle than red light, separating the colours. From the ground, you can only see light refracted through drops above you, so you see the familiar semi-circular rainbow. Colin Leonhardt, in a helicopter with the sunset behind him and a rain shower ahead, saw refracted and reflected light from both above and below—forming a full circular rainbow. Australian Weather Calendar/Colin Leonhardt

Australia's largest selling calendar is back again with a series of exquisite photographs that depict the extraordinary diversity of the country's landscape. The calender has gained appreciation over the last few years and continue to grow in popularity.

According to Vicki Middleton, more than 60,000 weather calenders were sold in 2014. In addition, copies of it were posted in more than 80 countries. The striking statistics make the calender one of the most popular and colorful items exported from the country.

"This multi-award-winning calendar provides a platform for the Australian community to connect with their environment through the art of photography, while serving as an educational resource on our unique weather and climate," said Vicki, in a press release. "This year we received more than 800 entries, which made it a really tough job to whittle down to the winning images."

The images showcased in the calender range from a fogbow and a full-circle rainbow to a fallstreak hole and dark clouds over sand dunes. The meteorological explanation provided at the bottom of each photograph aptly compliments that of the Bureau of Meteorology's vision to promote environmental intelligence among Australians.

The Australian Weather Calender is prepared each year by the Bureau with the help of a network of volunteers. The participants are provided with a copy of the calender annually. The calender is a way to recognize the contribution of the volunteers who roam around the country and help the Bureau take a note of the temperature, water and climate data.

The Australian Weather Calendar was first published by the Bureau of Meteorology and the Australian Meteorological and Oceanographic Society in 1985. A copy of the 2016's calender can be purchased from the Bureau shop.