Big Bang theory – Origin of the Universe v. Big Bang marks the beginning of the universe • Occurred about 15 billion years ago • All matter and space was created v. Not a huge explosion that hurled matter in all directions. Technically, there was no “bang” v. Technically, matter is not moving outward in all directions. Reality: space expands
Raisin bread analogy of an expanding universe
Origin of the Universe
The structure of the Universe A galaxy is a collection of billions of stars held together by gravity The universe contains billions of galaxies and each galaxy contains billions of stars. Our galaxy is a spiral galaxy called the Milky Way
What makes objects in space keep moving? 1. Gravity -- a force of attraction between objects Greater mass = greater gravity Greater distance = less gravity Weight is a measure of the pull of gravity Is weight the same as mass? NO! Weight changes due to gravity; mass stays the same 2. Inertia -- an object in motion stays in motion and an object at rest stays at rest, unless acted on by a different force
What would life be like without gravity?
Rotation vs. Revolution Rotation: an object spinning on its axis Revolution: an object orbiting around another object or point in space
Two forces keep objects moving in space: 1. gravity – the force of attraction between objects with mass 2. inertia – an object will continue doing what it’s doing unless acted on by a different force
Gravity pulls gases and dust in space together to form planets, moons, and stars
Where do stars come from? Stars form in nebulae where gases condense and nuclear fusion reactions generate tons of energy
Betelgeuse Orion Nebula Rigel
Not all stars in a constellations are actually near each other All stars are not alike in size, color, or brightness
Stars are very different from each other, depending on their mass and place in their life cycle HIGH MASS STARS LOW MASS STARS
Our Sun is actually a very average star in the middle of it’s life cycle. . medium brightness , temperature, and size Stars form in gas nebulas They enter the main sequence at various points depending on how much mass they collect The Sun (and our solar system) is about 5 billion years old.
Stars get their energy from nuclear fusion