Earth And The Solar SystemCopy

O Level / IGCSE Physics Cheat Sheet – 6.1 The Earth and the Solar System

6.1.1 The Earth

Basic Astronomical Facts:

• Earth is a planet that orbits the Sun once every ≈ 365 days.
• Earth’s orbit is elliptical but almost circular.
• Earth rotates on its axis once every ≈ 24 hours.
  • Tilt of axis causes seasons.
• The Moon orbits Earth in ≈ 27.3 days (~1 month).
• Light from the Sun takes ≈ 500 seconds (8 minutes 20 seconds) to reach Earth.

Average Orbital Speed Equation:
v = 2πr / T

Where:

• v = orbital speed (m/s)
• r = average radius of orbit (m)
• T = orbital period (s)

Used to calculate the speed of orbiting objects such as Earth around the Sun.

6.1.2 The Solar System

Components of the Solar System:

• One star: The Sun.
• Eight planets (in order from the Sun):
  1. Mercury
  2. Venus
  3. Earth
  4. Mars
  5. Jupiter
  6. Saturn
  7. Uranus
  8. Neptune
• Minor planets:
  • Dwarf planets (e.g., Pluto)
  • Asteroids in the asteroid belt (between Mars and Jupiter)
• Moons: Natural satellites that orbit planets.
• Smaller bodies:
  • Comets (icy bodies with elliptical orbits)
  • Other natural satellites

Planetary Data Interpretation:

• Data can include:
  • Orbital distance (AU or km)
  • Orbital period (days/years)
  • Density (kg/m³)
  • Surface temperature (°C or K)
  • Gravitational field strength (N/kg)

Gravitational Field Strength (g):

• Increases with the mass of the planet.
• Decreases with distance from the planet.

Mass and Gravity of the Sun:

• Sun contains ≈ 99.8% of the Solar System’s total mass.
• Sun’s gravitational field strength is greater than that of any planet.

Orbits and Gravitational Force:

• The Sun’s gravity provides the centripetal force keeping planets in orbit.
• As distance from the Sun increases:
  • Gravitational pull decreases
  • Orbital speed of planets decreases