File:Null spherical space (special relativity).jpg
Wikipedia for Schools...
Wikipedia for Schools was collected by SOS Children's Villages. SOS Childrens Villages is an international children's charity, providing a good home and loving family to thousands of children who have lost their parents. We also work with communities to help vulnerable families stay together and raise children in the best possible environment. Sponsoring a child is a great way to help children who need your support.