Space Physics

• Universe


  • Galaxy
  • Stars
  • Planets
• The Universe consists of billions of galaxies
• Our Galaxy


  The Milky Way (It consists of billions of stars)
• Our solar system is part of the Milky Way
• Day and Night


  The Earth spinning on its axis, making one complete rotation in 24 hours
• The Earth


  • One of the eight planets of the Solar system
• Causes of different Seasons

  • The rotation of the Earth around the Sun
  • The tilt of the Earth's axis (23.5°) to the plane of its path around the Sun
  • The different daylight hours and the angle of the sun between summer and winter
• Moons


  Natural Satellites
• Gravity of the Moon

  1/6 from the gravity of Earth, as it has 1/6 from its mass (g=1.64 N/kg)
• Phases of the Moon

  1. New Moon (fully dark)

  2. Waxing Crescent

  3. Half Moon

  4. Waxing Gibbous

  5. Full Moon

  6. Waning Gibbous

  7. Half Moon

  8. Waning Crescent

  9. New Moon
• Contents of the Solar System

  • The Sun (it's a star that represents more than 99% of the mass of the solar system)
  • Eight planets
  • Natural and artificial satellites
  • Dwarf planets (ex: Pluto)
  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune
• Types of planets


  • 4 inner rocky planets
  • 4 outer gaseous giants
• Planets


  • Orbiting the Sun due to the gravitational force of the sun
  • Closer planets experience higher gravitational force, more curved path, faster rotation, shorter time period, higher surface temperature
  • 4 inner rocky planets have higher density than 4 outer gaseous planets
  • 4 outer gaseous planets have larger mass than 4 inner rocky planets
• Comets


  • They orbit the sun due to gravity in very elliptical orbits
  • They have long orbital periods
  • They have tails of gas and dust
• As the comet gets closer to the sun

  Its speed increases
• Reason for increase in comet speed

  As gravitational force increases, law of conservation of energy: as GPE decreases so KE has to increase to keep total amount of energy constant
• Asteroids


  • Minor planets made of rocks, metals and minerals that orbit the sun
  • They are larger in numbers than comets
  • Belt of asteroids between mars and Jupiter
• Origin of the Solar System (Accretion Model)

  1. Gravity pulls the material (Hydrogen) from Interstellar clouds forming Nebula

  2. Spinning of material forming flat Accretion Disc

  3. As material attracted towards the centre forming Protostar, GPE converts to KE and then Heat Energy, so Fusion starts

  4. Heavy materials pulled towards the centre by Gravity, while lighter materials pushed away by Solar Wind

  5. Solar system formed (4 Rocky planets + 4 Gaseous planets)
• Gravitational Force between two masses m1 & m2

  Inversely proportional to the distance squared
• The Milky Way


  Spiral Galaxy (contains billions of stars)
• Light year


  1 light year = 9.5 x 10 15 m
• The Sun


  • Medium sized star consisting mainly of hydrogen and helium (75% Hydrogen + 24% Helium + 1% other elements as oxygen and carbon)
  • Produces energy by nuclear fusion of hydrogen into helium
  • Fusion needs high temperature to provide high KE (speed) for atoms to Fuse and overcome repulsive forces between positive nuclei
  • Emits radiations mainly in the form of Infrared, Visible light and Ultraviolet
  • Inside the Sun, the matter exists in the form of Plasma (completely ionized gas/positive ions + electrons)
• Types of stars


  • Small stars ("Small and Medium" like the Sun and up to 8 times larger than our Sun)
  • Giant (Large) stars (more than 8 times larger than our Sun)
• Life Cycle of Small Stars

  1. Nebula: cloud of hydrogen gas and dust

  2. Protostar: young star gathering its mass from interstellar cloud or a Nebula

  3. Main sequence (stable) star: As the protostar's temperature increases, nuclear fusion starts to take place in the core of the star (H+H = He), at this point the outward force due to expansion (Radiation Pressure) = the inward gravitational force

  4. Red giant: New fusion reactions occur around the core (Fusion of He atoms)

  5. Planetary Nebula

  6. White Dwarf -> Black Dwarf
• Life Cycle of Giant Stars

  1. Nebula cloud of hydrogen gas and dust

  2. Protostar: a young star gathering its mass from interstellar cloud or a Nebula

  3. Main sequence (stable) star: As the protostar's temperature increases, nuclear fusion starts to take place in the core of the star (H + H = He), at this point the outward force due to expansion (Radiation Pressure) = the inward gravitational force

  4. Red Supergiant: A new series of fusion reactions occur around the core (Fusion of He atoms)

  5. Supernova: Explosion of a massive star forming nebula containing heavier elements

  6. Neutron Star or Black hole
• The Big Bang theory


  Explosion of a point with very high temperature and density, causing the universe to expand
• Age of Solar system = 4.5 billion years
• Age of Universe (Big Bang) 14 billion years
• Doppler Effect


  • Difference between the source frequency and the observed frequency due to relative motion between the source and the observer
  • Approaching: Frequency ↑ Wavelength↓
  • Receding (moving away): Frequency ↓ Wavelength ↑
• Evidence for the big bang theory


  • Red shift of distant galaxies: light from surrounding galaxies is red-shifted as they are moving away from the Earth, further galaxies are moving faster than nearby galaxies
  • Cosmic microwave background radiation (CMBR): Microwave radiations observed at all points in space around the Earth, radiation was produced when the Universe was formed, radiation expanded into Microwave region of electromagnetic spectrum (as wavelength increases)
• Red shift


  observed wavelength is longer and shifted towards the red end of the spectrum, as the surrounding galaxies are receding from the Earth
• How Speed and Distance of a distant galaxy are measured

  1. Speed: using the change in wavelength due to the redshift of its color

  2. Distance: using the brightness of the supernova happening in this galaxy
• Hubble's law


  The speed of recession of the galaxy "v" is directly proportional to its distance "d" away, v=H. d
• The Hubble constant (H₂)

  Defined as the ratio of the speed at which the galaxy is moving away from the Earth to its distance from the Earth, Ho=2.2x10-18 per second
• The age of the universe = 1/Ho = 1/(2.2x10-18) = 4.5x10¹7 s = 1.4 × 10 10 years (14 billion years)