Astronomy Unit 1: Scale of the Universe

Study Notes

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.