Space: Universe, Galaxies, Stars, and the Solar System

Universe

  • The Universe contains all space, matter, energy, and time.
  • It is home to at least 100 billion galaxies and is approximately 13.8 billion years old based on measurements of the oldest stars and the expansion rate of the universe.

Galaxies

  • Galaxies are vast collections of gas, dust, stars, and their solar systems, bound by gravity.
  • The Milky Way is our galaxy, containing the Sun and at least 100 billion stars. The diameter of the Milky Way is about 100,000 light-years.

Stars

  • A star is a body in space made of gas that generates its own light (e.g., the Sun).
  • The Sun consists mainly of hydrogen (91%) and helium (9%) and radiates energy across infrared, visible, and UV regions of the electromagnetic spectrum.

Solar System

  • The Solar System consists of one star (the Sun), eight planets in the following order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
  • Additionally, it contains minor planets, dwarf planets (e.g., Pluto), moons, comets, and asteroids.
  • The four inner planets (Mercury, Venus, Earth, Mars) are rocky and small, while the outer planets (Jupiter, Saturn, Uranus, Neptune) are gaseous and large.

Light-Year

  • Astronomical distances are measured in light-years, where 1 light-year equals the distance traveled by light in one year, approximately 9.5imes10159.5 imes 10^{15} meters.

Earth

  • Earth rotates on its tilted axis (approx. 24 hours for a complete rotation), resulting in day and night.
  • It orbits the Sun once every approximately 365 days, and the Moon orbits Earth approximately every month, causing the cyclical phases of the Moon.

Definitions

  • Planet: A large body made of rock or gas that orbits a star and does not emit light.
  • Dwarf Planet: Similar to a planet but smaller and orbits a star.
  • Moon: A rocky body orbiting a planet, also called a natural satellite.
  • Orbit: A regular, repeating path one object in space takes around another, typically elliptical.

Major Components of the Solar System:

  • Asteroids: Small rocky objects, remnants from the Solar System's formation, primarily found in the asteroid belt between Mars and Jupiter.
  • Comets: Bodies of dust and ice that orbit the Sun.
  • Meteors: Pieces of rock or dust that create streaks of light when entering Earth's atmosphere.
  • Meteorites: Fragments of meteors that reach Earth's surface.

Planetary Characteristics**

  • Mercury: Smallest planet, surface temperature varies significantly.
  • Venus: Hottest planet, thick atmosphere mainly composed of carbon dioxide.
  • Earth: Supports life, with a balanced atmosphere.
  • Mars: Known for its potential for past life, has two moons.
  • Jupiter: Largest planet with a gaseous surface and many moons.
  • Saturn: Known for its prominent rings, composed largely of gas.
  • Uranus: Ice giant, with a blue color from methane in the atmosphere, has rings and numerous moons.
  • Neptune: Farthest planet, known for its strong winds and deep blue color.

Moon Phases**

  1. New Moon: Moon is between Earth and the Sun, not visible from Earth.
  2. Waxing Crescent: A small sliver of the Moon becomes visible.
  3. First Quarter: Half of the Moon is visible.
  4. Waxing Gibbous: More than half is visible.
  5. Full Moon: Entire face of the Moon is illuminated.
  6. Waning Gibbous: More than half is still visible but decreasing.
  7. Last Quarter: Half is visible but opposite to the First Quarter.
  8. Waning Crescent: The last sliver visible before the New Moon again.

Light Travel Time

  • Light travels at approximately 3imes1083 imes 10^8 m/s. For example:
    • Time for light to reach Mercury is approximately 3.4 minutes.
    • Time taken for sunlight to reach Neptune can be similarly calculated based on its distance from the Sun.