Unit 1: A Modern View 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 increasingly larger units (e.g., Street, City, Country) to locate a specific point in the universe.
- Locating Earth for aliens requires specifying the minimum information: size, location, and distance within the known universe.
- Our galaxy, the Milky Way, contains roughly 3000 years worth of star counts if you could count one star per second.
- Galaxies are grouped into clusters and superclusters, forming the known universe.
- Common units in astronomy include astronomical units (AU), light-years (ly), and parsecs (pc). Light years and parsecs are units of distance, not time.
Units of Measurement in Astronomy:
- Astronomical unit (AU): measuring distances within our solar system
- Light year (ly): length light travels in one year
- Parsec (pc): another astronomical unit, also a measure of distance
Ramifications of Distance:
- Observing distant objects in the universe reveals a look back in time.
- Sunlight takes 8 minutes to reach Earth, so we see the Sun as it was 8 minutes ago.
- Distanced objects offer a look into the past because the time it takes the light from distant stars and galaxies to reach Earth. The farther away an object is, the longer its light takes to travel, giving us a glimpse into its past.
Scale of the Solar System:
- If the Sun were scaled to the size of a basketball, then the planets would take up very little space. Mercury, the closest planet to the Sun on this scale, would be roughly the size of a <1cm ball-bearing.
Important Distances:
- Precise conversions are provided in the text, relating measurements of various objects to relevant units.
Scientific Notation:
- Scientific notation is used for large and small values in science because it makes expressing these values more easily.
- Powers of 10 are used to represent large or small numbers.
1.2 The History of the Universe:
- Observations show the universe is expanding, implying all the universe's mass started in a single point.
- This beginning, the Big Bang, occurred about 14 billion years ago.
- The term singularity describes the theoretical infinite density of mass in the beginning phase of the universe.
Cosmic Epochs:
- The text displays a timeline, showing major events in the history of the universe, from the Big Bang to the present-day formation of galaxies.
Cosmic Calendar:
- Represents the history of the universe in a simplified year, showing when significant events like the formation of the first stars, planets, life, and human civilization occurred during the year.
1.3 Spaceship Earth:
- A phrase coined by Buckminster Fuller to describe our solar system's journey through spacetime.
- Rotation: spinning of Earth on its axis
- Orbit: Earth's path around the Sun
- Earth tilts on its axis at 23.5°.
- The celestial plane describes how the stars rotate relative to Earth's equator.
- Galaxies move relative to each other. Hubble discovered a relationship.
Raisin Cake Analogy:
- Explaining how objects appear to move away as the universe expands.
- The further away, the faster the object moves relative to the observer.