Earth and Space: Earth-Sun Relationships

Course Context and Objectives

This lecture introduces Earth-Sun relationships as the foundation for understanding physical geography.
It is a required course for students also enrolled in human geography and the geography minor.
Objectives:
- Understand the Earth's context within the universe.
- Understand the Earth-Sun relationship, including planetary motion, radiation, and seasonal differences on Earth's surface.

The Universe

Definition: The known universe refers to all known matter and energy existing in space and time.
- Matter: A physical substance that occupies space and has mass.
- Mass: A measure of inertia or the strength of gravitational attraction. It quantifies the amount of physical substance in an object.
  - Crucial Distinction: Mass is not the same as weight.
    - Example: An astronaut in space has mass (takes up space, is substantial) but has little weight. On Earth, her mass remains the same, but her weight would change (she would have weight).
- Energy will be discussed further with solar radiation.
The Big Bang Theory:
- This theory describes the creation of the universe as we know it.
- It is based on Albert Einstein's theory of relativity.
- Summary: Approximately $13.7$ billion years ago, everything was concentrated in a single point, which then exploded. The universe is still expanding outward.
- Things at the edges of the expanding universe are moving away faster than things at the center. This is because objects with mass are gravitationally attracted to one another, and objects at the edges have fewer other massive objects to attract them.
Key Vocabulary Terms:
- Density: (Briefly mentioned) The heaviness of a substance, e.g., a car sinks in water due to its density.
- Temperature: A measure of hotness or coldness, reflecting the amount of kinetic energy of the atoms that make up a substance.
  - Example: Air temperature reflects the kinetic energy (vibration) of air molecules.
Dimensions of the Universe:
- The Big Bang explosion has certain dimensions, thought of as having a radius.
- The radius of the observable universe is roughly $47$ billion light-years across.
Light-Year Explained:
- A light-year is the distance light can travel in one Earth year.
- Light travels at approximately $300,000 ext{ km/s}$ .
- Therefore, one light-year is roughly $9.5$ trillion kilometers.
- Distances in Solar System Context:
  - Earth is approximately $8$ light-minutes away from the Sun (light takes $8$ minutes to reach us).
  - It would take roughly $1.87$ light-years to reach the edge of our solar system.
  - Metaphor/Example: Distances between planets are immense; for perspective, if planets were scaled down and the sun was at one point, Neptune might be in a distant town (e.g., Sackville if originating from here).

The Milky Way Galaxy

Definition: Our galaxy, the Milky Way, is a collection of stars (like our Sun), interstellar gases, dust, and other space matter held together by gravity.
Gravity in Space vs. Earth:
- On Earth: Gravity causes objects to fall to the ground.
- In Space: Gravity is the attractive force between objects with mass.
  - Factors influencing gravitational pull:
    - Mass: Larger masses exert stronger gravitational pull.
    - Proximity: Closer objects have stronger gravitational attraction.
    - Example: Mercury, Venus, and Earth are closer to the Sun and experience stronger gravitational attraction compared to distant planets like Neptune and Pluto.
Galaxy Formation:
- Galaxies began forming around $13.6$ billion years ago, after the Big Bang.
- As primordial matter from the explosion expanded, some elements remained close and large, attracting one another gravitationally.
- These masses started to rotate around each other, leading to decreasing temperatures and condensation of heavier particles towards the centers, forming galaxies and solar systems.

Our Solar System

Location: Our solar system resides in one of the spiral arms of the Milky Way galaxy.
Structure: It is centered around our Sun, with planets and other celestial bodies orbiting it.
The Sun:
- Mass: The Sun has the vast majority of the solar system's mass (approximately $99.86$ %).
- Temperature: Very hot (stated as $15.8$ degrees; context implies this is a simplified or misstated temperature, as core temperature is millions of Kelvin).
- Energy Emission: It emits light and heat that travels through space as solar wind.
- Light Travel Time: Sunlight reaches Earth in approximately $8$ minutes.
- Variations in Intensity: Solar intensity is affected by:
  - Sunspots: Darker, cooler areas on the Sun's surface that are regions of intense magnetic field activity. They can form cycles and, during intense periods, affect technological systems on Earth.
  - Solar Flares: (Briefly mentioned).
- State of Matter: The Sun is composed of plasma.
  - Four States of Matter:
    1. Solid: Particles tightly bound (e.g., rock).
    2. Liquid: Particles connected but can flow (e.g., water).
    3. Gas: Particles separated and move freely (e.g., air).
    4. Plasma: A moldable, almost