Stars and Constellations Exploring the Universe’s
Guiding Lights
• Stars are massive, luminous spheres of hot gases (mainly
Introduction hydrogen and helium) held together by gravity.
to Stars
• A star’s lifecycle is determined by its mass, nuclear fusion
converts hydrogen to helium, releasing energy that makes
the star shine.
Formation
of Stars
Stars form from clouds of dust and
gas called nebulae. Gravity pulls
particles together, increasing
pressure and temperature until
nuclear fusion begins.
The process follows Jeans
Instability Criterion, where a cloud
collapses if its internal pressure
can’t resist gravitational forces.
Classification of Stars
• 📌 Basic: Stars are classified by
temperature and brightness into the
Hertzsprung-Russell (H-R) Diagram
categories: O, B, A, F, G, K, M (from
hottest to coolest).
📌 Advanced: Spectral classification also
considers ionization levels, with the Sun
being a G2V-type main-sequence
star.
Types of Stars
White Dwarfs (small, Neutron Stars
Main Sequence Red Giants (old,
hot remnants of dead (super-dense
Stars (like the Sun) expanded stars)
stars) collapsed cores)
Chandrasekhar
Tolman-
Limit (1.4 Solar
Black Holes Oppenheimer-
Masses): Determines
(collapsed massive Stellar remnants Volkoff (TOV) Limit:
whether a star
stars with immense depend on mass: Determines if a
becomes a white
gravity) neutron star collapses
dwarf or undergoes a
into a black hole.
supernova.
Nebula → 2. Protostar → 3. Main
Sequence → 4. Red Giant → 5.
White Dwarf / Supernova → 6.
Neutron Star or Black Hole
Life Cycle Fusion process differs: Low-
mass stars (PP Chain reaction),
of a Star high-mass stars (CNO cycle).
Core collapses due to electron
degeneracy pressure in white
dwarfs or neutron degeneracy
pressure in neutron stars.
What Are
Constellation
s?
• Constellations are patterns
of stars forming
recognizable shapes, often
named after mythological
figures.
Constellations are not real
star groupings; they appear
close due to perspective but
can be light-years apart.
Major Constellations & Their Myths
Orion (The Hunter) – Greek mythology, represents a warrior.
Ursa Major & Ursa Minor (Big and Little Bears) – Contains the North
Star (Polaris).
Cassiopeia – Named after a vain queen in Greek mythology.
Leo – Represents a lion from Greek mythology.
Ancient civilizations used constellations for navigation and agricultural
cycles.
Zodiac Constellations
The Zodiac consists of 12 Due to precession of the equinoxes,
constellations along the Sun’s apparent the Zodiac positions shift
path (ecliptic), including Aries, Taurus, approximately every 26,000 years.
Gemini, etc.
How Stars and Constellations
Help in Astronomy
Used for navigation (e.g., Basis for early calendars Astrometry: Measuring Standard Candles:
sailors using Polaris). and timekeeping. star positions to understand Cepheid variables and
galaxy structure. supernovae help measure
cosmic distances.
Exoplanets and Star Systems
Some stars have planetary
systems (like our Sun),
called exoplanetary Exoplanets are detected
systems. using:
Radial Velocity Method:
Transit Method:
Detecting star “wobbles”
Observing brightness dips.
due to gravitational pull.
Fun Facts & Trivia
• The Sun is 4.6 billion years old and will turn into a red giant in 5 billion years.
• The brightest star in the night sky is Sirius in Canis Major.
• Some stars orbit each other in binary systems.
• A binary system refers to a star system where two stars orbit around a common center
of mass. These stars are gravitationally bound to each other, and they can either be
visible from Earth as two distinct stars or may be too close together to resolve separately.
• Betelgeuse in Orion is expected to explode as a supernova in the next 100,000 years.
• Neutrinos from the Sun pass through Earth every second in huge numbers.
Conclusion
• Stars and constellations shape our understanding of
the universe, from ancient myths to modern
astrophysics.
• "We are all made of star stuff" – Carl Sagan 🌟
