The year 2009 was International Year of Astronomy, and to celebrate, asked you what you'd most like to know about your Universe in a series of online polls. The project, kindly supported by the Royal Astronomical Society, came up with seven questions, which we put to world-leading astronomers and cosmologists. Below are their answers in seven articles, as well as some podcasts.
What is dark matter?
Martin Rees, Astronomer Royal and Professor of Cosmology and Astrophysics at the University of Cambridge, explores the mysterious substance that makes up 25% of the Universe.
What is dark energy?
It's what makes the Universe expand faster and faster. Find out more with John D. Barrow.
How long is a day?
We put the question to Nicholas Mee and here is his answer. And it's not 24 hours!