Khan Academy Static

Stellar parallax can be used for "nearby" stars, but what if we want to measure further out? Well this tutorial will expose you to a class of stars that helps us do this. Cepheids are large, bright, variable stars that are visible in other galaxies. We know how bright they should be and can gauge how far they are by how bright they look to us.

10665_Cepheid_variables_1.html

10666_Why_cepheids_pulsate.html

10667_Why_gravity_gets_so_strong_near_dense_objects.html