P8

• What pulls dust and gas together in space?

  Gravity
• What is a nebula?

  A cloud of dust and gas in space
• What are all naturally occurring elements produced by?

  Fusion in stars
• How are elements heavier than iron formed?

  By supernovae
• What happens to a star as it becomes a main sequence star?

  It gets denser and temperature rises
• What starts in a star's core during hydrogen fusion?

  Outward pressure from fusion
• What balances the inward force of gravity in a star?

  Outward pressure from fusion
• What is a red supergiant?

  A star larger than the Sun
• What happens when hydrogen nuclei begin to run out in a star?

  The star begins to evolve
• What is a red giant?

  A star the size of the Sun
• What do smaller stars fuse up to?

  Heavier elements up to iron
• What is a neutron star?

  A dense remnant of a massive star
• What is a white dwarf?

  A small, dense star remnant
• What can massive stars become after a supernova?

  A black hole
• What is a black dwarf?

  A cold, dead remnant of a star
• What do supernovae eject into the universe?

  Elements that can form new planets
• What is our solar system a part of?

  The Milky Way galaxy
• What does our solar system contain?

  Sun, planets, moons, and satellites
• How do planets orbit the Sun?

  In elliptical paths
• What are artificial satellites?

  Man-made objects in orbit
• What keeps planets and satellites in circular orbits?

  Gravitational force
• What happens to an object's direction in a circular orbit?

  It constantly changes
• What does a constant change in direction mean for an object's velocity?

  Its velocity constantly changes
• What remains constant for an object in a circular orbit?

  Its speed
• What happens if the speed of an object in a stable orbit changes?

  The radius of the orbit changes
• What is the relationship between orbit radius and speed?

  Smaller radius means faster travel
• What is the speed of an object in a circular orbit at $42 \text{ km/s}$?


  $42 \text{ km/s}$
• What is the speed of an object in a circular orbit at $30 \text{ km/s}$?


  $30 \text{ km/s}$
• What is red-shift?

  An increase in light wavelength
• When is red-shift observed?

  When a galaxy moves away from Earth
• What happens to the speed of distant galaxies?

  They move away faster
• What does greater red-shift indicate?

  A greater distance from Earth
• What does red-shift provide evidence for?

  The universe is expanding
• What does the Big Bang theory propose?

  All matter was in a dense, hot space
• What does the expansion of space support?

  The Big Bang theory
• What is one mystery of the universe?

  Why distant galaxies recede at increasing speeds
• What is another mystery of the universe?

  Dark matter
• What is the third mystery of the universe?

  Dark energy
• What misconception is mentioned about dark energy?

  It is confused with solar energy