This poll is now closed. The most popular question was: "How does gravity work?" You can read the answer on Plus, or listen to the podcast. Thank you for taking part and don't forget to vote in the current poll!

This is the fourth online poll in our series to celebrate the International Year of Astronomy 2009. Choose your favourite question from the list on the right, and we'll put the one that proves most popular to world-leading astronomers and cosmologists, including Astronomer Royal Martin Rees and author and cosmologist John D. Barrow. The poll will remain open for a month and the answer will be published in a Plus article and podcast soon after. If your most burning question is not on this list, then leave a comment on this blog and we'll endeavour to include it in a future poll — there will be three more polls dotted throughout the year.

The most popular questions in the first two polls were What happened before the Big Bang? and Are the constants of nature really constant?. Read the answers by clicking on the links, and discuss them on our blog. The third poll came up with the question "What are dark energy and dark matter?" and we will publish the answer on Plus shortly.

Labels: IYA2009