NDA (I) Shaurya 1.0
The Universe & Solar sytem
➢ What is the Universe?
● The universe is a vast, infinite space containing millions of galaxies.
● It includes all of space, time, matter, and energy, serving as the ultimate backdrop for
the story of existence.
● Understanding the universe involves multiple scientific fields, such as astronomy, physics,
and cosmology.
● The study of the universe covers its origin, structure, evolution, and unsolved mysteries
that still intrigue scientists.
● A star is a celestial body that generates its own heat and light.
● A galaxy is a system consisting of millions of stars.
● The light from the nearest star to the Sun, Proxima Centauri, takes about four years to
reach Earth.
● The scientific study of the universe is known as cosmology.
● A light year is the distance light travels in one year through a vacuum, about 9.46
trillion km. It is a unit of distance, not time, used in astronomy and space geography to
measure vast cosmic distances, such as between stars, galaxies, and other celestial
bodies.
Early Theories on the Origin of the Earth:
, ● Nebular Hypothesis (Kant–Laplace, 1796): Planets formed from a rotating
cloud of gas and dust around the young Sun.
● Revised Nebular Theory (Otto Schmidt & Weizsäcker, 1950): Solar nebula
of hydrogen, helium, and dust condensed through friction and collisions to
form planets.
Modern Theories on the Origin of the Universe:
➢ Big Bang Theory: The universe began ~13.7 billion years ago from an
extremely hot, dense point that exploded and expanded.
➢ Edwin Hubble’s Evidence: Galaxies are moving apart, showing the universe is
expanding.
➢ Stages:
➢ Matter concentrated in a tiny “ball.”
➢ Explosion (Big Bang).
➢ Expansion and cooling — formation of atoms and galaxies.
➢ Alternative Theory: Steady State Theory (Hoyle) — universe remains
constant (less accepted).
Star Formation:
● In the early universe, matter and energy were unevenly distributed, causing
differences in gravitational forces.
● This led to matter clustering together, eventually forming galaxies, which
contain large numbers of stars.
● Galaxies are spread over vast distances measured in light-years, with
diameters ranging from 80,000 to 150,000 light years.
The Universe & Solar sytem
➢ What is the Universe?
● The universe is a vast, infinite space containing millions of galaxies.
● It includes all of space, time, matter, and energy, serving as the ultimate backdrop for
the story of existence.
● Understanding the universe involves multiple scientific fields, such as astronomy, physics,
and cosmology.
● The study of the universe covers its origin, structure, evolution, and unsolved mysteries
that still intrigue scientists.
● A star is a celestial body that generates its own heat and light.
● A galaxy is a system consisting of millions of stars.
● The light from the nearest star to the Sun, Proxima Centauri, takes about four years to
reach Earth.
● The scientific study of the universe is known as cosmology.
● A light year is the distance light travels in one year through a vacuum, about 9.46
trillion km. It is a unit of distance, not time, used in astronomy and space geography to
measure vast cosmic distances, such as between stars, galaxies, and other celestial
bodies.
Early Theories on the Origin of the Earth:
, ● Nebular Hypothesis (Kant–Laplace, 1796): Planets formed from a rotating
cloud of gas and dust around the young Sun.
● Revised Nebular Theory (Otto Schmidt & Weizsäcker, 1950): Solar nebula
of hydrogen, helium, and dust condensed through friction and collisions to
form planets.
Modern Theories on the Origin of the Universe:
➢ Big Bang Theory: The universe began ~13.7 billion years ago from an
extremely hot, dense point that exploded and expanded.
➢ Edwin Hubble’s Evidence: Galaxies are moving apart, showing the universe is
expanding.
➢ Stages:
➢ Matter concentrated in a tiny “ball.”
➢ Explosion (Big Bang).
➢ Expansion and cooling — formation of atoms and galaxies.
➢ Alternative Theory: Steady State Theory (Hoyle) — universe remains
constant (less accepted).
Star Formation:
● In the early universe, matter and energy were unevenly distributed, causing
differences in gravitational forces.
● This led to matter clustering together, eventually forming galaxies, which
contain large numbers of stars.
● Galaxies are spread over vast distances measured in light-years, with
diameters ranging from 80,000 to 150,000 light years.
