How old are the children to be immunized?

Tens of thousands of health workers will go house to house over the next three days in an effort to immunize 63 million children under the age of five in sub-Saharan Africa. The campaign is the start of monthly national immunization days during the low season for polio. It’s hoped that vaccinating children now--when the virus is at its weakest--will be the best way of stopping transmission.

Scientists are beginning to nail down the minimum age of the universe, with the latest estimate put at 12.5 billion years. Scientists can determine the age of the universe by fixing the age of the oldest stars in the Galaxy.