3: The Universe Last updated Jan 14, 2021 Save as PDF 2.6: Summary 3.1: Introduction to the Universe Page ID12749 ( \newcommand{\kernel}{\mathrm{null}\,}\) 3.2: Video- The History of Our World in 18 Minutes3.3: Expanding Universe3.4: Formation of the Universe3.5: Dark Matter and Dark Energy3.6: Star Systems3.7: Types of Galaxies3.8: Milky Way Galaxy3.9: Star Energy3.10: Star Classification3.11: Measuring Distant Stars