Introduction to Astronomy

Posted on Aug 25, 2024 in Geology

Planetary System

A planetary system consists of one or several central stars and planets orbiting around them.

  • Planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
  • Dwarf Planets: Pluto, Eris, Ceres, Makemake, Orcus, Sedna…

Celestial Motion

  • Planets revolve around stars.
  • Satellites revolve around planets.
  • Comets revolve around the Sun. A comet is a ball of gas and dust with a tail.
  • Asteroids orbit within a star system. When entering a planet’s atmosphere, they disintegrate and fall as meteorites.

Galaxies and the Universe

  • Galaxies are formed by multitudes of stars, which may be surrounded by planets.
  • The Solar System is located in the Milky Way galaxy.
  • The universe is a vast collection of galaxies.

Hubble and the Doppler Effect

Galaxies emit light waves of a given wavelength. The most distant galaxies have a larger wavelength, indicating they are moving away from us. This observation supports the theory of the expansion of space.

The Big Bang

The Big Bang, which occurred approximately 14 billion years ago, is the prevailing cosmological model for the universe.

  • All matter and energy were concentrated at a single point and then began to expand rapidly.
  • Subatomic particles came together to form larger particles.
  • For the first 300,000 years, the universe consisted mainly of hydrogen and helium atoms.

Evidence for the Big Bang

  • Cosmic background radiation present throughout the universe.
  • Abundance of hydrogen and helium.

Distances in Space

The distance between stars is measured in light-years.

Stellar Evolution

Stars Like the Sun

  1. Gas Cloud (Hydrogen): The life cycle of a star begins with a cloud of gas, primarily hydrogen.
  2. Star (Hydrogen Fusion; 10 Million Years): The gas cloud collapses under gravity, leading to nuclear fusion of hydrogen in the core and the birth of a star.
  3. Red Giant Star: When the hydrogen in the core is depleted, the star expands into a red giant, fusing hydrogen in its outer layers.
  4. White Dwarf Star: Eventually, the star sheds its outer layers, leaving behind a dense, hot core known as a white dwarf. The star fades as the remaining hydrogen is consumed.

Stars 10 Times Bigger Than the Sun

  1. Gas Cloud: Similar to smaller stars, these stars originate from a massive gas cloud.
  2. Star (Hydrogen Fusion; 2-3 Million Years): The intense gravity causes a faster rate of hydrogen fusion, resulting in a shorter lifespan.
  3. Red Supergiant: As hydrogen depletes, the star expands into a red supergiant, fusing heavier elements in its core.
  4. Supernova: The star explodes in a supernova event, releasing immense energy and scattering heavy elements into space.
  5. Neutron Star: The core collapses further, forming an extremely dense neutron star.
  6. Pulsar: Some neutron stars rotate rapidly, emitting beams of radiation, and are known as pulsars.

Stars 30 Times Larger Than the Sun

  1. Gas Cloud: These massive stars form from enormous gas clouds.
  2. Star (Hydrogen Fusion; 2-3 Million Years): The extremely high mass leads to rapid hydrogen fusion and a short lifespan.
  3. Red Supergiant: The star expands into a red supergiant as it consumes its fuel.
  4. Supernova: A catastrophic supernova explosion marks the end of its life.
  5. Black Hole: The core collapses under its own gravity, forming a black hole, a region of spacetime where gravity is so strong that nothing, not even light, can escape.

Formation of the Solar System

The Solar System formed from a rotating cloud of gas and dust known as a solar nebula. A protoplanetary disk, with the proto-Earth at its center, accumulated particles that eventually coalesced to form the Moon.

Layers of the Earth

The Earth’s internal structure is composed of distinct layers, with denser materials concentrated towards the core.

  • Crust: The outermost layer, divided into oceanic and continental crust.
  • Mantle:
    • Upper Mantle: Includes the asthenosphere, a viscous layer.
    • Lower Mantle: Denser and hotter than the upper mantle.
  • Core:
    • Outer Core: Liquid iron and nickel, responsible for Earth’s magnetic field.
    • Inner Core: Solid iron and nickel due to immense pressure.

Constellations and Astrology

  • A constellation is a group of stars that form a recognizable pattern when viewed from Earth. Imaginary lines connect the stars to create these patterns.
  • Ancient civilizations used constellations for navigation and to track seasons.
  • The zodiac is a belt of the sky divided into twelve equal parts, each named after a constellation. It represents the Sun’s apparent path throughout the year.
  • Astrology attempts to predict human affairs and personality traits based on the positions of celestial objects. However, it lacks scientific validity.
  • Astronomy is the scientific study of celestial objects, their movements, and the universe as a whole.

From Aristotelian to Copernican Thought

  • Aristotle (4th Century BC): Believed in a geocentric model, with Earth at the center of the universe.
  • Democritus (4th Century BC): Proposed that celestial orbits were elliptical and that the universe extended far beyond Earth.
  • Eratosthenes (3rd Century BC): Calculated the Earth’s circumference and demonstrated its spherical shape.
  • Ptolemy (2nd Century AD): Developed a comprehensive geocentric model that remained influential for centuries.
  • Copernicus (16th Century): Proposed the heliocentric model, placing the Sun at the center of the solar system, based on earlier ideas by Aristarchus of Samos (3rd Century BC).
  • Galileo Galilei (17th Century): His observations with the telescope, along with Johannes Kepler’s laws of planetary motion, provided strong evidence for the heliocentric model.
  • Harlow Shapley (20th Century): Demonstrated that the Sun is not at the center of the Milky Way galaxy, but rather situated in its outskirts. This supported the idea of an even larger and more complex universe.

Theory of Plate Tectonics

Developed by Alfred Wegener, and later refined by Harry Hess and Robert Dietz, the theory of plate tectonics explains the movement of Earth’s lithosphere.

  • Tectonic Plates: The Earth’s lithosphere is divided into several large and numerous smaller tectonic plates.
  • Major Plates: North American, South American, Pacific, Eurasian, Indo-Australian, Antarctic.
  • Types of Plates:
    • Continental: Composed mainly of continental crust (e.g., Arabian Plate).
    • Mixed: Contain both continental and oceanic crust (most plates).
    • Oceanic: Made entirely of oceanic crust (e.g., Pacific Plate).
  • Plate Boundaries: The areas where tectonic plates meet are called plate boundaries. There are three main types:
    • Divergent Boundaries: Plates move apart, allowing magma to rise and create new crust. This process is associated with earthquakes, volcanic eruptions, and the formation of mid-ocean ridges.
    • Convergent Boundaries: Plates move towards each other, leading to subduction (one plate sliding beneath the other) or collision.
      • Subduction: Occurs when oceanic lithosphere meets another plate, resulting in deep ocean trenches, volcanic arcs, and powerful earthquakes.
      • Collision: When two continental plates collide, they buckle and uplift, forming mountain ranges. This process is also associated with earthquakes.
    • Transform Boundaries: Plates slide past each other horizontally. These boundaries are characterized by intense seismic activity and are known as transform faults.