States of Matter: https://phet.colorado.edu/sims/html/states-of-matter-basics/latest/states-of-matter-basics_en.html
Phases of the Moon: https://www.youtube.com/watch?v=a-pt_P8_7gM&feature=related
Solar System: https://www.bobthealien.co.uk/sun/index.htm
The Size of the Universe: https://www.youtube.com/watch?v=TXfOzhZGtNw