Chapter 1 of G.C. Leong’s Certificate Physical and Human Geography, titled “The Earth and the Universe,” covers fundamental astronomical concepts and the physical characteristics of our planet.
Exploring the Universe
- Stars and Galaxies: Stars are millions of times larger than Earth. They occur in massive clusters called galaxies (or nebulas), with the Milky Way estimated to contain about 100,000 million stars.
- Light Distance: Light from the Sun takes roughly 8 minutes to reach Earth, while light from the nearest star (excluding the Sun) takes about four years.
The Solar System
- Sun: The center of the system, with a surface temperature of 6,000°C and a core reaching 20 million°C. It is roughly 300,000 times larger than Earth.
- Planets: All nine planets (including Pluto, in older editions) revolve around the Sun in elliptical orbits.
- Mercury: Smallest and closest to the Sun.
- Venus: Considered “Earth’s twin” due to similar size, mass, and density.
- Mars: Notable for potential plant life and human exploration interest.
- Jupiter: The largest planet, composed mostly of gases like hydrogen and helium.
- The Moon: Earth’s only natural satellite, revolving eastward around Earth once every 27 days.
The Shape of the Earth
The Earth is not a perfect sphere but a geoid (oblate spheroid), slightly flattened at the poles and bulging at the equator. Proofs of its sphericity include:
- Circumnavigation: Ferdinand Magellan’s voyage (1519–1522) proved no “edge” exists.
- The Circular Horizon: The horizon always appears circular and widens with altitude.
- Ship’s Visibility: A ship’s mast is seen before its hull when approaching the horizon.
- Sunrise and Sunset: Occur at different times globally; if Earth were flat, they would occur simultaneously everywhere.
- Lunar Eclipses: The shadow cast by Earth on the Moon is always an arc of a circle.
Earth’s Movements
- Rotation: Earth rotates from west to east on its axis every 24 hours, causing day and night.
- Revolution: Earth orbits the Sun every 365¼ days (a year), causing the seasons.
- Inclination: The axis is tilted at 66½° to the plane of the ecliptic, leading to varying lengths of day and night and seasonal changes.
Latitude and Longitude
- Latitude: Angular distance north or south of the Equator (0°).
- Longitude: Angular distance east or west of the Prime Meridian (Greenwich), used to calculate Standard Time and the International Date Line
