Notes: Ch.1 - Our Place in the Universe

What is our place in the universe?

• Our "cosmic address" would be considered:

•  SOLAR SYSTEM -> PLANET -> LOCAL GROUP/ANDROMETER -> UNIVERSE

• STAR - A large, glowing ball of gas that generates heat and light through nuclear fusion (sun)
• SOLAR SPOTS -  (on stars) are like acne/blemishes on people
• PLANET - A moderately large object that orbits a star; it shines by reflected light. Planets may be rocky; icy, or gaseous in compositionicy.
• MOON (OR SATELLITE) - An object that orbits a planet.
• ASTEROID - A relatively small and rocky object that orbits a star.
• COMET - A relatively small and icy object that orbits a star.
• SOLAR (STAR W/ PLANETS) SYSTEM - A star and all the material that orbits it, including its planets and moons.
  
• NEBULA - An interstellar cloud of gas and or dust.
  
• GALAXY - A great island of stars in space, all held together by gravity and orbiting a common center. (black hole in center of it)
• UNIVERSE -  The sum total of all matter and energy; that is, everything within and between all galaxies.

 How did we come to be?

• The expansion of the universe began with the BIG BANG. The universe continues to expand, but on smaller scales gravity has pulled matter together to make galaxies.

Galaxies as comic Recycling Plants: 

• The early universe contained only TWO chemical elements: HYDROGEN & HEILIUM... all other elements, INCLUDING US (HUMANS), were created by exploding stars within galaxies...from their 'star dust.'

Life Cycles of Stars:

• Many generations of stars have lived & died in the Milky Way! 
• CYCLE:
• 1.) STARS EXPLODE & SCATTER THE ELEMENTS THEY'VE PRODUCED INTO SPACE 2.) STARS ARE BORN IN CLOUDS OF GAS & DUST (PLANETS AS WELL)                  3.) STARS SHINE WITH ENERGY RELEASED BY NUCLEAR FUSION, RESULTS IN MANUFACTURING ALL ELEMENTS HEAVIER THEN HYDROGEN & HELIUM    

Earth & Life:

• Solar System was born 4.5 billion years ago, about 2% of the original hydrogen & helium was converted into heavier elements.

How can we know what the universe was like in the past?

LIGHT YEAR - The distance light can travel in one year: 10 trillion kilometers (6 trillion miles)

• Light travels at a finite speed: 300,000 KM/S
• The farther away we look in the distance, the farther back we look in time.
• At great distances, we see objects as they were when the universe was much younger. 
• NO, we can't see the entire universe. (observable universe)