Universe & The Solar System

Ancient Hindu

• Ancient Indians believed the universe had a beginning.

• They imagined a cyclical universe of
  endless creation and destruction.

• A mysterious creator may have started it all—or maybe not.

Ancient Greek

Many believed that the cosmos was neither created nor it is perishable, and that it was timeless and infinite in extent. From these thinkers also came the idea of the universe having a center.

Philolaus

“Earth was the center of the universe” - (first to propose it) but a central fire around it which the sun, moon, and the planets, and other celestial objects revolved uniformly.

Aristarchus

Supported the Geocentric idea but suggested that the central fire was the sun.

Aristotle

Proposed that the center of the cosmic is the Earth. His geocentric cosmology like his philosophical and scientific works in general, dominated all studies and speculations until the 16th century,

Ptolemy

Popularized and advanced the geocentric model wherein heavenly bodies revolved around a stationary Earth placed at the center of the universe. Explained the epicyle, deferent, and eccentric paths (Ptolemic model).

Albert Einstein

In 1919, after he introduced the Theory of General Relativity, he declared a new cosmological view: the universe was a finite and static four dimensional closed sphere. His universe was homogeneous, where matter spread smoothly throughout space.

Big Bang Theory

• Many hypotheses explain the universe’s origin.

• This is the most widely accepted theory today.

• Cosmologists estimate the universe is about 13.7 billion years old.

• The universe’s history is divided into eras.

• Each era marks major changes in the
  universe’s conditions.

• Proposed by Albert Einstein.

The Planck Theory

• The four fundamental forces were once unified as a "super force."

• This idea comes from quantum mechanics and general relativity.

• Matter and energy were equivalent in the early, very hot universe.

• Gravity separated ("froze out") from the super force.

• This separation initiated the shaping of the universe.

• 10-43^ seconds after the Big Bang.

The Grand Unified Theory Era

• The GUT era began when the super force split into gravity and the GUT force (lasting only a fraction of a second).

• Occurred when the universe cooled to about 10²⁹ K.

• The nuclear strong force separated from the GUT force.

• This released huge energy, causing rapid expansion of the universe, inflation.

The Electroweak Theory

• The universe kept expanding and cooling, reaching 10¹⁵ K at 10⁻¹⁰ second old.

• The electromagnetic and weak forces separated from the electroweak force.

• By the end of this era, the four fundamental forces were fully distinct.

The Particle Era

• After the forces separated, ordinary particles began to form.

• There was spontaneous creation and annihilation of particles.

• Photons collided to form matter and antimatter (e.g., electrons, neutrinos, quarks).

• As the universe cooled, quarks combined to form protons and neutrons.

The Era of Nucleosynthesis

• Big Bang nucleosynthesis (BBN) occurred 10 seconds to 20 minutes after the Big Bang.

• During this time, light atomic nuclei formed through nuclear fusion.

• This era determined the abundance of hydrogen, helium, and trace lithium in the universe.

The Era of Nuclei

• he Era of Nuclei lasted from 3 minutes to 380,000 years after the Big Bang.

• The universe was a hot plasma of hydrogen, helium nuclei, and free electrons.

• Ended when the universe cooled enough for electrons to combine with nuclei, forming neutral atoms.

• This made the universe transparent to light.

The Steady State Theory

• The universe has no beginning or end.

• It proposed a constantly expanding universe with a constant average density.

• New matter (mainly hydrogen) is continuously created to fill expanding space.

• The universe appears the same at all times and places.

• This theory is now largely discarded.

The Oscillating Theory

• A cyclical process of expansion and contraction.

• After a Big Bang, the universe expands, then collapses in a Big Crunch.

• A new Big Bang follows, restarting the cycle.

• The process is eternal and repeating, with each cycle having its own beginning and end.

The Big Crunch Theory

• A theoretical future of the universe.

• It suggests the universe will stop expanding and collapse inward.

• Gravity would overpower expansion, leading to contraction.

The Structure of the Universe

• The universe has a hierarchical
  structure, from small to large.

• Planets → stars → solar systems →
  galaxies → clusters →
  superclusters.

• All are connected through a vast
  cosmic web made of
  filaments, sheets, and voids.

• Shaped by dark matter and gravity

Solar System

• Planets and bodies orbiting a star (e.g., our Sun).

• Is located in the Milky Way galaxy.

• It lies in a minor spiral arm called the
  Orion Arm or Orion Spur.

• This arm is between the Sagittarius
  and Perseus arms.

• The Solar System is about 27,000
  light-years from the galaxy’s center.

Galaxy

A massive system of billions of
stars, gas, and dust held by gravity.

Universe

The largest scale, containing all galaxies and everything in them.

The Milky Way

• Our home galaxy, a barred spiral galaxy.

• Contains hundreds of billions of stars, including the Sun.

• Named after the milky band of light seen in the night sky.

• Appears as a band due to the combined light of stars and gas clouds.

• Roughly 100,000 light-years wide.

• Has a supermassive black hole at its center.

The Nebular Theory

(Formation of Stars and Planetary Systems)

• Explains how stars and planetary systems form.

• Begins with a nebula — a large cloud of gas and dust.

• The nebula collapses under gravity and
  flattens into a disk.

• A star (sun) forms at the center, with planets
  orbiting around it.

Planet Formation

(The Nebular Theory)
Within the protoplanetary disk, particles collide and clump together through a process called accretion, eventually forming planetesimals and then planets.

Temperature Zones

(The Nebular Theory)
Closer to the protostar, it's hotter, leading to the formation of rocky planets (like Earth), while further out, it's cooler, allowing for the formation of gas giants (like Jupiter).

Sun

• The central star of our solar system.

• Its gravity keeps all planets and objects in orbit.

• This star’s interaction with Earth affects: seasons, ocean currents, weather, and climate

• There are billions of stars like this one in the Milky Way galaxy.

The Inner (Terrestrial) Planets

• Mercury, Venus, Earth, and Mars.

• Have rocky compositions and solid surfaces.

• Located closer to the Sun.

• Made mostly of silicate rocks and metals, unlike the gas giants.

Outer (Gas/Ice Giants) Planets

• Jupiter, Saturn, Uranus, and Neptune.

• Also called gas giants (Jupiter, Saturn) and ice giants (Uranus, Neptune).

• Much larger and more massive than the inner planets.

• Composed mainly of hydrogen and helium (gas giants), and hydrogen, helium, and ices (ice giants).

The Moons

• There are over 200 moons (natural satellites) in the solar system.

  Planets with moons:

• Earth – 1 moon

• Mars – 2 moons

• Jupiter – at least 92 moons

• Saturn – 82 moons

• Uranus – 27 moons

• Neptune – 14 moons

• Some dwarf planets, like Pluto, also have moons.

Asteroids

• Rocky, airless remnants from the early solar system.

• Mostly found in the asteroid belt between Mars and Jupiter.

• Vary in size — from a few meters to hundreds of kilometers.

• Total mass of all ___ is less than Earth’s Moon.

Comets

• Icy, small bodies made of ice, dust, and rock ("dirty snowballs").

• They are remnants from the early solar system.

• Mostly found in the Kuiper Belt (short-period comets) and Oort Cloud (long-period comets).

Dwarf Planets

Ceres, Pluto, Haumea, Makemake, and Eris. Ceres is located in the asteroid belt, while the other four are in the Kuiper Belt, a region beyond Neptune.

Liquid Water (Earth)

Covers about 70% of the planet, is essential for all known life forms and plays a critical role in Earth's climate and geological processes.

Atmosphere (Earth)

Composed of nitrogen and oxygen, with a mix of other gases like carbon dioxide and water vapor. This regulates temperature, protects from harmful solar radiation, and provides the necessary gases for life.

Climate (Earth)

Earth's axial tilt and distance from the sun create a relatively stable ___, allowing for the evolution and survival of complex life forms. The presence of liquid water, a moderate greenhouse effect, and a stable orbit contribute to this stability.

Goldilocks Zone

This zone, is defined by a specific distance from a star where temperatures are just right – not too hot, not too cold – for liquid water to exist on a planet's surface. Earth's orbital position, atmospheric composition, and other factors contribute to its ability to sustain life.

Magnetic Field (Earth)

Earth's molten iron core generates a that deflects harmful solar and cosmic radiation. This protection is crucial for shielding life from dangerous radiation. Unlike other inner planets, Earth possesses a _ generated by the movement of molten iron in its outer core, a process called the geodynamo.

Presence of Life (Earth)

Earth is currently the only known planet to harbor this. The unique combination of factors mentioned above has allowed for the development and evolution of a vast array of life forms.