ASTRONOMY

Theories about the Origin of the Universe and Solar System, Kinds of Galaxies Phases/ Life Cycle of a Star, Famous Stars and Constellation, Comets and Asteroids, Quasars and Pulsars + Blazars and Seyferts, Planets of the Solar System, Sun: The layers and different activities, Characteristics/ Notes about the Moon + Phases of the Moon, Tides, Lunar and Solar Eclipse

Big Bang Theory

The prevailing theory that the universe originated from an extremely hot and dense singularity about 13.8 billion years ago

Steady State Theory

A now largely rejected theory suggesting that the universe has no beginning or end and continuously creates new matter as it expands

Oscillating Universe Theory

Suggests that the universe undergoes endless cycles of expansion and contraction

Inflation Theory

An extension of the Big Bang that proposes a rapid exponential expansion of space in the first moments of the universe

Nebular Hypothesis

Explains the origin of the solar system as forming from a rotating cloud of gas and dust (nebula) that collapsed under gravity

Protoplanet Hypothesis

States that planets formed from collisions and accretion of planetesimals within a protoplanetary disk

Capture Theory

Suggests that planets and other celestial bodies were captured by the sun's gravitational pull

Binary Star Hypothesis

Proposes that the solar system formed as a result of interaction between two stars, one being the sun

Spiral Galaxy

Has a central bulge with arms that spiral outward; includes the Milky Way

Elliptical Galaxy

Shaped like a flattened sphere; contains mostly older stars and little gas or dust

Irregular Galaxy

No definite shape; often result of galaxy collisions or gravitational interactions

Barred Spiral Galaxy

A spiral galaxy with a central bar-shaped structure of stars

Life Cycle of a Low-Mass Star

Nebula → Protostar → Main Sequence Star → Red Giant → Planetary Nebula → White Dwarf → Black Dwarf

Life Cycle of a High-Mass Star

Nebula → Protostar → Main Sequence Star → Red Supergiant → Supernova → Neutron Star or Black Hole

Nebula

A vast cloud of dust and gas; the birthplace of stars

Protostar

A contracting cloud of gas and dust with enough mass to form a star

Main Sequence Star

The longest phase in a star’s life where hydrogen fusion occurs in the core

Red Giant

An expanded, cooler star that occurs after hydrogen in the core is exhausted

Supernova

A massive explosion of a dying massive star

Neutron Star

The dense core left behind after a supernova of a medium to high-mass star

Black Hole

An extremely dense object with gravity so strong that not even light can escape

White Dwarf

A small, dense, hot remnant of a low-mass star after the planetary nebula phase

Sirius

The brightest star in the night sky, located in the constellation Canis Major

Betelgeuse

A red supergiant star in the constellation Orion

Polaris

Also known as the North Star; located nearly directly above Earth’s north pole

Rigel

A blue supergiant star in the constellation Orion

Alpha Centauri

The closest star system to Earth, after the sun

Orion

A prominent constellation known as "The Hunter"

Ursa Major

A constellation known for containing the Big Dipper

Ursa Minor

A constellation containing Polaris (the North Star)

Cassiopeia

A W-shaped constellation in the northern sky

Scorpius

A bright, summer constellation known for the star Antares

Taurus

A constellation with the bright star Aldebaran; associated with the Pleiades cluster

Comets

Icy celestial bodies from the outer solar system that develop tails when near the sun due to sublimation

Parts of a Comet

Nucleus (solid core), Coma (glowing gas and dust), Ion Tail (gas), Dust Tail (particles)

Asteroids

Rocky objects mostly found in the asteroid belt between Mars and Jupiter

Meteoroid

A small piece of an asteroid or comet that travels through space

Meteor

The streak of light when a meteoroid enters Earth's atmosphere (shooting star)

Meteorite

A meteoroid that survives its passage through Earth’s atmosphere and lands on the surface

Quasars

Extremely luminous and active galactic nuclei powered by supermassive black holes; among the most distant objects

Pulsars

Highly magnetized, rotating neutron stars that emit beams of electromagnetic radiation

Blazars

A type of quasar with a relativistic jet pointed directly toward Earth; very energetic

Seyfert Galaxies

A class of galaxies with bright nuclei that show strong emission lines from highly ionized gas

Terrestrial Planets

The four inner planets: Mercury, Venus, Earth, and Mars; rocky and dense

Gas Giants

The large outer planets: Jupiter and Saturn; composed mainly of hydrogen and helium

Ice Giants

Uranus and Neptune; planets with icy components and thick atmospheres

Mercury

Closest planet to the sun; has no atmosphere and extreme temperature variations

Venus

Second planet from the sun; thick CO₂ atmosphere causes a strong greenhouse effect

Earth

The third planet; only known planet to support life, with water and oxygen-rich atmosphere

Mars

Fourth planet; known as the Red Planet; has the largest volcano and dust storms

Jupiter

The largest planet; has a Great Red Spot and dozens of moons including Ganymede

Saturn

Known for its extensive ring system; second-largest planet in the solar system

Uranus

Tilted on its side; has a pale blue color due to methane in the atmosphere

Neptune

Farthest planet; known for strong winds and deep blue color; has the moon Triton

Sun

The central star of our solar system; provides light and energy through nuclear fusion

Core

The innermost layer of the sun where nuclear fusion occurs, producing energy

Radiative Zone

The layer where energy moves outward from the core via radiation

Convective Zone

The outer layer of the sun’s interior where heat is transferred by convection

Photosphere

The visible surface of the sun; emits the sunlight we see

Chromosphere

The layer above the photosphere; appears reddish during solar eclipses

Corona

The outermost layer of the sun's atmosphere; extends millions of kilometers into space

Solar Flares

Sudden, intense bursts of radiation from the sun’s surface

Sunspots

Dark, cooler regions on the photosphere caused by magnetic activity

Coronal Mass Ejections (CMEs)

Massive bursts of solar wind and magnetic fields released into space

Solar Wind

A stream of charged particles emitted by the sun that affects space weather and Earth’s magnetosphere

Moon

The Earth's only natural satellite; 1/6 of Earth’s gravity; no atmosphere; surface covered in craters, maria, and highlands

Rotation and Revolution of the Moon

Both take about 27.3 days, causing the same side to always face Earth (synchronous rotation)

Moon’s Gravity

Causes tides on Earth; weaker than Earth's due to smaller mass

Phases of the Moon

Caused by the changing position of the Moon relative to the Earth and Sun; completes a cycle in ~29.5 days

New Moon

The moon is between Earth and Sun; the side facing Earth is not illuminated

Waxing Crescent

Thin crescent of light appears on the right; increasing illumination

First Quarter

Half of the moon is visible (right side); 1/4 through the cycle

Waxing Gibbous

More than half is lit on the right side; approaching full moon

Full Moon

The entire face of the moon is illuminated; Earth is between Moon and Sun

Waning Gibbous

Light decreases; still more than half lit, but now on the left

Last Quarter

Half of the moon is visible (left side); 3/4 through the cycle

Waning Crescent

Thin crescent of light on the left; decreasing illumination

Tides

The rise and fall of ocean levels due to gravitational pull of the Moon (mainly) and Sun

High Tide

Occurs on the sides of Earth closest to and farthest from the Moon due to gravitational pull and inertia

Low Tide

Occurs at 90° angles from the Moon; water is pulled away from these regions

Spring Tide

Higher high tides and lower low tides; occurs during full and new moons (Sun and Moon aligned)

Neap Tide

Lower high tides and higher low tides; occurs during first and last quarters (Sun and Moon at right angles)

Solar Eclipse

Occurs when the Moon passes between the Earth and Sun; blocks sunlight from reaching Earth

Lunar Eclipse

Occurs when Earth passes between the Sun and Moon; Earth's shadow falls on the Moon

Total Solar Eclipse

The Moon completely covers the Sun as viewed from Earth

Partial Solar Eclipse

Only part of the Sun is obscured by the Moon

Total Lunar Eclipse

The Moon passes entirely into Earth's umbra (darkest shadow)

Partial Lunar Eclipse

Only part of the Moon passes through Earth's umbra

Penumbra

The lighter outer shadow of Earth or Moon; causes partial eclipses

Umbra

The darkest inner shadow; causes total eclipses

Eclipse Season

Periods (~twice a year) when the Sun, Earth, and Moon align to allow eclipses