Descriptive Astronomy 101
Origin of the Universe & Solar System

Origin of the Universe

Vesto Slipher, 1912
Lowell Observatory (Lowell Observatory web page link)
Observations of distant galaxies
Determined that they were moving relative to us
M31 - The Andromeda Galaxy is approaching at 300 km/s
Observed 41 galaxies moving away at speeds of 1800 km/s

How was this rate of retreat or approach determined?

Based on variations in the wavelengths of light (radiation)
Each color is part of the visible spectrum
Image of the visible spectrum of light

Galaxy produces specific wavelengths of radiation - ex. yellow light
If the galaxy is not moving relative to us, we see yellow light
If the galaxy is moving towards us, we see the light as blue
If the galaxy is moving away from us, we see the light as red
This is the Doppler Shift or Doppler Effect

Edwin Hubble and Milton Humason

Determined the distance to galaxies
Standard Candle
Determined that the farther away the galaxy is, the faster away from us it is moving.

Standard Model of the Big Bang

Expansion of the universe
Everything is moving away from everything else
Results from the expansion of space itself
Initial conditions of very high density
300,000 years after initial expansion the first stable atoms form
Hydrogen (H) - Most abundant - 92%
Helium (He) and Lithium (Li) - Least abundant

The Early Universe

Galaxies form as large clouds of hydrogen and helium separated from other clouds
Stars form as smaller clouds of hydrogen and helium separated from other clouds within the forming galaxies
Population II stars - low metal stars, mostly H and He
Population II stars burn their nuclear fuel
- The most massive go Supernova
Contraction of these gases into Population I stars - metal-rich stars
Population I stars form from Population II materials
Population I live then die - Supernova
Becomes gas cloud again
Present generation of stars - Population I

Formation of the Solar System: The Solar Nebula

Approximately 5 billion years ago, gas and interstellar dust which came from nearby stellar explosions (Population II stars) began condensing to form a solar nebula
Nebula is defined as an interstellar cloud of gas or dust
Any theory that explains the formation of the Solar System must account for the characteristics of the Solar System

General Characteristics

All the planets revolve around the Sun in the same direction
All the planets lie in a common plane - the plane of the Ecliptic
The orbits of the planets are nearly circular
Most planets have axes of rotation that are nearly perpendicular to the ecliptic
The Sun has a relatively slow rotation
Inner planets are made of rocks and metals
Outer planets are made of gases and ices

Nebular Theory

Contraction of the Solar Nebula gases was primarily due to gravity
Contraction of the nebula results in rotation
Most material falls into the sun - 90%
Build up of sufficient mass starts nuclear reactions
The Sun lights up
Blast of energy clears the Solar System of left over gas and dust

Outer Regions of the Solar Nebula

Outer regions of solar nebula are cooler than the central regions
Liquid and solid particles form and begin clumping together due to collisions, gravity and static electricity
High temperature material forms solid material in the inner Solar System - metals and silicates
Low temp. material forms solids in the outer Solar System - ices (water, methane, ammonia)

Homogeneous Accretion

Small material collides forming larger material
Planetesimals form as collisions continue (asteroids, meteoroids and comets)
Large planetesimals collide with each other
Formation of a protoplanet results from continued collision
Heating occurs in the protoplanet due to: ?
Differentiation occurs
Differentiation is the separation of materials due to density differences
Planet Earth develops with a core of iron and nickel, and a crust of silicates as differentiation continues

Inhomogeneous Accretion

The iron and nickel core of the planet condensed first from the Solar Nebula
These materials solidify at higher temp. and would be the first solids to form
Iron and magnesium silicates condensed next
Aluminum and potassium silicates, water and gases condenses last
Differentiated Planet Earth forms

Homogeneous or Inhomogeneous?