With her stories about how to urinate in space, and photographs of floating chocolates and jelly babies, a Nasa astronaut kept hundreds of schoolgirls spellbound yesterday. Catherine Coleman, who has been an astronaut since 1992, has participated in several space missions, including spending 159 days in orbit on the International Space Station.Speaking at Wynberg Girls' High School, in Cape Town yesterday, she said science, technology and maths were not just for boys.Coleman explained that being in a low-gravity environment changed everything and made every aspect of life a science experiment."Without all that gravity we get to see what liquids really want to do - what shape the drops want to take. We also see how differently fire behaves in space because the flame on a candle back home looks different to a flame up there. And as for crystal growth, crystals are more perfect up there so we discover more about how they form."Nasa chief scientist Ellen Stofan told the high school pupils that only about 20% of the scientists in her field were women."We lose girls interested in maths and science all along the way, from school onwards. Sometimes it feels like women have to be twice as good to be taken half as seriously."Stofan is an expert on the geology of Venus, Mars, Saturn's moon Titan, and Earth.She and Coleman are in South Africa as part of a delegation to the recent SciFest Africa festival in Grahamstown...