Astronomy Unit 1: Scale of the Universe

Unit 1: A Modern View of the Universe

• 1.1 The Scale of the Universe

  • A "Cosmic Address" would need progressively larger units (e.g., street, city, country) to locate an object.
  • To locate Earth, a detailed address is required, encompassing various levels of scale.
  • The minimum information needed includes units such as astronomical unit (AU), light-years (ly), and parsecs (pc).
  • Our galaxy, the Milky Way, contains roughly 3000 years' worth of stars if counted at one per second.
  • Galaxies form groups, and larger groups form clusters.
  • Superclusters are collections of clusters and isolated galaxies to make the known universe.
  • Units (or dimensions) are important for disseminating data across disciplines in astronomy, such as AU, light-years, and parsecs.
  • The scale of the solar system can be visualized by comparing the Sun to a basketball, and the size of other planets to objects in relation to the basketball (e.g., Earth would be much smaller).
  • The further into the universe we look, the further back in time we are observing, due to the time it takes for light to travel.

• 1.2 The History of the Universe

  • All astronomical observations indicate an expanding universe (increasing distances between objects).
  • This suggests that at one point, all universe mass resided in the same point in space.
  • This starting point is called the Big Bang, and it happened approximately 14 billion years ago.
  • The concept of singularity signifies a point of infinite density.
  • Density is defined as mass divided by volume (p = mass/volume).
  • Scientific notation is a more efficient way to express very large and small numbers in science.

• 1.3 Spaceship Earth

  • The Earth orbits the Sun and rotates on its axis.
  • The Earth's axial tilt is 23.5 degrees.
  • The ecliptic plane is the plane of the Earth's orbit around the Sun. The celestial plane defines the apparent daily motion of the stars centered on Earth's equator.
  • The Sun travels within the galaxy and relates to other stars.
  • The motion of galaxies relative to each other reflects both rotation and expansion.
  • The raisin-cake analogy can explain the expansion of the universe where the expansion creates distances between nearby objects.
  • The further away an object is, the younger it appears - as the light takes time to reach us.

• Cosmic Calendar

  • If the Big Bang occurred on January 1 at midnight, milestones (events) are compared in an analogy.
  • A 1-year timeline of events like the formation of planets, first life, etc.