Liz Bonnin presents a Horizon special about a rare and beautiful event in our solar system, one that we should all be able to see for ourselves - the transit of Venus across the face of the sun. It will start just before midnight of the 5th of June, and won't happen again for more than a century.

To celebrate its 50th birthday, Horizon invites the public to play a role in tackling the greatest challenges facing science today. This special episode of Horizon launches the £10 million Longitude Prize 2014 - a prize developed by Nesta, with Technology Strategy Board as funding partner, to find solutions to a new scientific challenge.

Over the last few years, our weather in Britain has become more extreme.

Last winter was the wettest ever recorded, as deadly storms battered the country for weeks on end. But previous winters have seen bitter lows of -22, as Britain was plunged into a deep freeze.

What everyone wants to know now is: why is our weather getting more extreme, can we expect to see more of it in the future, and has it got anything to do with climate change?

In this episode of Horizon, physicist Dr Helen Czerski and meteorologist John Hammond make sense of Britain's recent extreme weather and discover that there is one thing that connects all our recent extreme winters - the jet stream, an invisible river of air that powers along 10 km above us. What's worrying is that recently it has been behaving rather strangely.

Scientists are now trying to understand what is behind these changes in the jet stream. Helen and John find out if extreme winters are something we may all have to get used to in the future.

The Horizon team have gathered together a team of scientists and doctors to investigate the incredible, natural material that is growing out of our heads - our hair. With access to the research laboratories of some of the world's leading hair care companies, including L'Oreal and ghd, the team explore the latest cutting-edge research and technology designed to push the boundaries of hair and hair care.

Each one of us has a unique head of hair - an average of 150,000 individual hair strands growing approximately one centimetre every month. Over your lifetime, that is over 800 miles. The time and effort we put into styling, sculpting and maintaining this precious material has created a global hair care market worth a staggering £60 billion pounds. With such high stakes, it is inevitable that when developing hair-care products, science and business operate hand in hand. The team reveal how this industry science compares to the rigorous academic standards that they are used to.

These investigations also reveal why we care so much about our hair, and whether or not it is worth splashing out on expensive shampoos. They uncover the magic ingredients found in conditioners and lay bare the secrets of the shiny, glossy hair seen in the adverts.