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Index

  1. CCBY
  2. Last updated
    Jul 23, 2025
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A • B • C • D • E • F • G • H • I • J • K • L • M • N • O • P • Q • R • S • T • U • V • W • Y • Z

A

AbūalRayhān

14.4: Milky Way Galaxy Research

Absolute Zero

4.2: Thermal Radiation

absoluteMagnitude

11.22: The Hertzsprung-Russell Diagram

absorption line spectrum

4.4: Spectra

accessible

InfoPage

accretion

12.13: High-Mass Star Stellar Endings

accretion disk

12.12: Neutron Star and Companion Star Scenario

accretiondisk

12.8: White Dwarfs and Neighbors

ActionReactionLaw

2.11: The Mathematical Finish- Newton

active

13: Galaxies

active galaxies

13.6: Classification of Galaxies
13.10: Active Galaxies

activegalacticnuclei

13.12: Blazars- Quasar-like Object

adaptive optics

10.10: The National Solar Observatory

affordablelearningSolutions

InfoPage

afterglow

12.14: Gamma-Ray Bursts (GRBs)

age of the Universe

12.4: Stellar Evolution

age of Universe

15.7: Recent Data on the Universe

agn

13.2: Galaxies
13.12: Blazars- Quasar-like Object

agriculture

2.2: What Time Is It?

air burst

9.10: The Impact of Meteorites

Alpha Centauri

11.12: How Close are the Close-by Stars?

alternate theories

15.12: Religious or Philosophical Cosmology

alternativeTheories

15.9: Beyond the Big Bang

American Heritage Dictionary

15.12: Religious or Philosophical Cosmology

Anaxagoras

14.4: Milky Way Galaxy Research

ancient

9.3: What do you think?

ancient civilizations

2.2: What Time Is It?
2.3: Ancient Observations

ancient Greece

2.6: Claudius Ptolemy

ancient traditions

1.4: The Constellations

ancientcivilizations

14.1: What do you think?

Andromeda

11.18: Planispheres
13.15: Galactic Groups
14: The Milky Way Galaxy

Andromeda Galaxy

13.3: The History of Studying Galaxies
14.7: Andromeda Galaxy

AndromedaGalaxy

14.10: A Spinning Spiral

angles

11.10: Stellar Distances
11.14: Parsec Vs. Light-Year Measurement

angular resolution

5.1: The Telescope

Angular Sizes

3.3: The Sun and the Moon

Annie Jump Cannon

11.8: Star and Celestial Object Characteristics

anniejumpcannon

11.20: Spectral Type

Apollo11

11.6: Consider this…

Apophis

9.7: Asteroid Classification

apparent brightness

11.15: Stellar and Celestial Object Brightness

Aristotle

9.14: Comets in History
14.4: Milky Way Galaxy Research

artistic maps

11.17: Celestial cartography

asterism

1.5: Other Patterns

asteroid

9.10: The Impact of Meteorites
9.11: Comets

asteroid belt

9.5: Asteroids

asteroids

1.2: Basic Objects in the Universe
6.1: Our Solar System
6.4: The Nebular Theory - Other Important Evidence
7.4: Craters
7.12: Martian Moons
8.3: Rings
9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud
9.4: Minor Bodies
9.5: Asteroids
9.6: Brightest Asteroids Visible from Earth
9.7: Asteroid Classification
9.8: Meteoroids, Meteors, and Meteorites
9.18: The Centaurs- Are they Asteroids or Comets?

astrobiology

6.10: The Circumstellar Habitable Zone
10.1: What do you think?

astrology

2: Historical Astronomy
2.3: Ancient Observations
2.7: Astronomy and Astrology

astronauts

5.10: Hubble Space Telescope

Astronomers

11.18: Planispheres
13.16: Dark Matter

astronomical

1.3: Scale of the Cosmos

astronomical bodies

11.5: Star Clusters

astronomical class

12.3: Stellar Mass

astronomical discoveries

14.7: Andromeda Galaxy

astronomical distance

11.3: Cepheids

astronomical distances

11.14: Parsec Vs. Light-Year Measurement

astronomical events

12.10: High-Mass Stars

astronomical objects

12.7: Planetary Nebula

astronomical observations

13.3: The History of Studying Galaxies

astronomical phenomena

11.4: Cataclysmic Variables
12.4: Stellar Evolution
12.13: High-Mass Star Stellar Endings

astronomical research

15.7: Recent Data on the Universe

astronomical techniques

11.7: The Unknown in Astronomy

astrophotography

5.6: Images from the Telescope

astrophysics

6.5: The Nebular Theory - Proplyds
6.7: The Discovery of Extrasolar Planets
6.12: Extrasolar Planets
9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud
9.2: The Oort Cloud and Kuiper Belt
10.1: What do you think?
10.3: Our Star, the Sun
11.1: Module Introduction
11.2: Variable Stars
11.4: Cataclysmic Variables
11.6: Consider this…
11.15: Stellar and Celestial Object Brightness
11.18: Planispheres
11.19: Star Colors
12.4: Stellar Evolution
12.6: White Dwarf
12.9: Nova, Novae, and Supernova
12.12: Neutron Star and Companion Star Scenario
13.2: Galaxies
13.7: Elliptical Galaxies
13.8: Spiral Galaxies
13.11: Quasar-stellar Objects
14.8: X-Ray and Gamma-Ray of the Milky Way Galaxy
15.8: Issues with the Big Bang

atmosphere

7.5: Planet Mercury
7.6: Planet Venus
7.7: Planet Earth
7.10: Snow on Mars
7.13: Characteristics of the Solar System’s Rocky Planets
8.4: Planet Jupiter
8.6: Planet Saturn
8.8: Saturn’s Satellites
8.9: Planet Uranus
9.19: Pluto
10.11: NASA’s Heliophysics Science Division

atmospheric activity

8.10: Planet Neptune

atmospheric phenomena

9.14: Comets in History

atoms

4.4: Spectra
15.3: Physical Cosmology

atypical stars

11.7: The Unknown in Astronomy

Aurora

10.9: The Dark Side of the Sun

axis

3.4: Seasons and Seasonal Changes

B

Babylonians

2.2: What Time Is It?

background stars

11.11: Everything is Moving

baily's beads

3.6: Eclipses

BarredSpiral

14.2: The Milky Way — Our Home Galaxy

Battle of Hastings

9.14: Comets in History

beliefs

14.1: What do you think?

belt

9: Minor Bodies of the Solar System

Betelgeuse

11.19: Star Colors

Bible

2.4: Contributions to Science

Big Bang

15: Cosmology
15.1: What do you think?
15.3: Physical Cosmology

Big Bang Theory

15.12: Religious or Philosophical Cosmology

big crunch

15.11: Questions Regarding the Eventual Fate of the Universe

Big Dipper

1.5: Other Patterns

BigBang

15.4: The Big Bang in Eras
15.6: Big Bang Evidence
15.8: Issues with the Big Bang
15.9: Beyond the Big Bang

BigBangEvents

15.4: The Big Bang in Eras

BigCrunch

13.16: Dark Matter

binary neutron stars

12.11: Neutron stars

binary star

12.13: High-Mass Star Stellar Endings

Binary Stars

6.9: What We Have Learned about Stellar Systems and Extrasolar Planets?
11.1: Module Introduction
11.4: Cataclysmic Variables
11.8: Star and Celestial Object Characteristics
11.24: Types of Star Systems and Stars

binoculars

5.4: Telescope Optical Types

biology

12.1: Star Life

black dwarfs

12.7: Planetary Nebula

black hole

12.13: High-Mass Star Stellar Endings

blazars

13.10: Active Galaxies
13.12: Blazars- Quasar-like Object

blueshift

4.5: Moving Objects, Spectra, and the Doppler Effect

bodies

9: Minor Bodies of the Solar System

Brahe

2: Historical Astronomy
2.8: The Birth of Modern Astronomy

bright

9.3: What do you think?

brightness

10.3: Our Star, the Sun
11.2: Variable Stars
11.9: Distances to the Stars and other Celestial Objects
11.15: Stellar and Celestial Object Brightness
11.16: Magnitude System
11.18: Planispheres
13.13: Galaxies, Distance, and Age

brightness outburst

11.4: Cataclysmic Variables

brightness variations

11.7: The Unknown in Astronomy

brown dwarf

6.12: Extrasolar Planets

Buddhism

15.13: Views on Creation

C

calculations

11.13: Light-Years

Calculus

2.11: The Mathematical Finish- Newton

calendars

2.2: What Time Is It?

CaliforniaInstituteofTechnology

13.4: Hubble’s Major Contributions

Callisto

8.5: Jupiter’s Satellites

Canis Major

11.19: Star Colors

carbon

12.6: White Dwarf

carbon dioxide

7.6: Planet Venus
9.12: Comet Characteristics

carbon fusion

12.9: Nova, Novae, and Supernova

carbon sphere

12.7: Planetary Nebula

cartographers

11.17: Celestial cartography

Cassini

8.6: Planet Saturn
8.8: Saturn’s Satellites

cataclysmic

11: Stellar Properties

cataclysmic variables

11.2: Variable Stars
11.4: Cataclysmic Variables

CCD

5.6: Images from the Telescope

ccsy3.0

9.13: Images of Comets

celebration

11.6: Consider this…

celestial

1.4: The Constellations
5.5: Telescope Mounts
11: Stellar Properties
11.18: Planispheres

celestial bodies

6.1: Our Solar System

celestial cartography

11.17: Celestial cartography

celestial events

9.17: A Comet Impacts a Planet

celestial mechanics

2.9: Observations of Motion- Brahe, Kepler, and Galilei

celestial objects

9.11: Comets
9.18: The Centaurs- Are they Asteroids or Comets?

celestial observations

2.3: Ancient Observations

Celestial Sphere

3.3: The Sun and the Moon

celestialobjects

9.2: The Oort Cloud and Kuiper Belt
13.7: Elliptical Galaxies
14.1: What do you think?

Celsius

4.2: Thermal Radiation

Centaurus A

13.10: Active Galaxies

centralbulge

13.8: Spiral Galaxies

Cepheid variables

11.2: Variable Stars

Cepheids

11: Stellar Properties
11.3: Cepheids

Cepheidvariables

13.4: Hubble’s Major Contributions

Ceres

6.3: What is a Planet?
9.5: Asteroids
9.6: Brightest Asteroids Visible from Earth

chain reaction

10.2: Fission and Fusion

Characteristics

8.2: Gas Giant Planets
8.9: Planet Uranus
11: Stellar Properties
14.2: The Milky Way — Our Home Galaxy

charged particles

10.6: Solar Regions

Charon

6.3: What is a Planet?

charts

11.18: Planispheres

Chelyabinsk

9.10: The Impact of Meteorites

Chichén Itzá

2.3: Ancient Observations

children

11.1: Module Introduction

Chinese astronomy

2.3: Ancient Observations

Chiron

9.18: The Centaurs- Are they Asteroids or Comets?

Christian

2.4: Contributions to Science

Christian Huygens

8.7: Saturn’s Rings

chromosphere

10.7: Major Solar Features

circumstellar

6.10: The Circumstellar Habitable Zone

civilization

1.4: The Constellations

clear skies

14.1: What do you think?

cloud

9: Minor Bodies of the Solar System

clouds

7.9: Planet Mars

Clyde Tombaugh

9.19: Pluto

cold dark matter

15.7: Recent Data on the Universe

ColdDarkMatter

13.17: WIMPs and String Theory

collaboration

InfoPage

collision

9.7: Asteroid Classification
14.10: A Spinning Spiral

color

11.21: Sample Spectral Types
12.8: White Dwarfs and Neighbors

colorindex

11.23: The Four Hertzsprung-Russell Diagram Stellar Groups

colors

4.1: Looking at a rainbow, what do you see?
11.20: Spectral Type

colorTemperature

11.22: The Hertzsprung-Russell Diagram

coma

9.12: Comet Characteristics

comet

9.17: A Comet Impacts a Planet
9.20: Eris

comet appearances

9.15: Scientific Advances

comet discovery

9.11: Comets

comet nucleus

9.12: Comet Characteristics

comet observation

9.16: Halley’s Comet

comet observations

2.3: Ancient Observations

comet orbits

9.11: Comets

comet tail

9.12: Comet Characteristics

comets

1.2: Basic Objects in the Universe
6.1: Our Solar System
6.4: The Nebular Theory - Other Important Evidence
7.4: Craters
9.2: The Oort Cloud and Kuiper Belt
9.3: What do you think?
9.4: Minor Bodies
9.9: Meteorites
9.11: Comets
9.12: Comet Characteristics
9.14: Comets in History
9.15: Scientific Advances
9.18: The Centaurs- Are they Asteroids or Comets?

community

InfoPage

companion stars

12.12: Neutron Star and Companion Star Scenario

comparative planetology

7.2: Comparing Planets

comparing planets

7: The Rocky Planets

computersimulation

6.5: The Nebular Theory - Proplyds

concave mirror

5.3: Telescopic Observations

constellation

1.5: Other Patterns

constellations

1.1: Module Introduction
1.4: The Constellations
3.3: The Sun and the Moon

contemporary exploration

1.1: Module Introduction

continuous spectrum

4.4: Spectra

Controversy

13.5: Hubble’s Law

convection

10.6: Solar Regions

convectionzones

12.5: Low-Mass Stars

convective zone

10.6: Solar Regions

Copernican model

2.9: Observations of Motion- Brahe, Kepler, and Galilei

CopernicanRevolution

2.8: The Birth of Modern Astronomy

Copernicus

2.8: The Birth of Modern Astronomy

core

10.4: How the Sun Works
10.6: Solar Regions

core collapse

12.10: High-Mass Stars

corona

3.6: Eclipses
10.7: Major Solar Features

Coronal Mass Ejections

10.9: The Dark Side of the Sun

cosmic

5.7: Space-Based Telescopes

cosmic microwave background

15.11: Questions Regarding the Eventual Fate of the Universe

cosmic observations

14.7: Andromeda Galaxy

cosmic rays

12.9: Nova, Novae, and Supernova

CosmicDust

14.3: Milky Way Galaxy Satellites

CosmicExpansion

15.5: The Planck Era

cosmicexploration

9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud

CosmicMicrowaveBackground

15.6: Big Bang Evidence

CosmicVelocity

13.5: Hubble’s Law

cosmogony

15.2: In the beginning…

CosmologicalRedshift

15.6: Big Bang Evidence

cosmology

14.5: Galileo Galilei, First to See the Milky Way Galaxy
14.6: The Milky Way Galaxy’s Shape
15: Cosmology
15.1: What do you think?
15.2: In the beginning…
15.3: Physical Cosmology
15.4: The Big Bang in Eras
15.7: Recent Data on the Universe
15.8: Issues with the Big Bang
15.9: Beyond the Big Bang
15.13: Views on Creation

cosmos

11.6: Consider this…

crater sizes

7.4: Craters

craters

7.3: Rocky Planets
7.4: Craters
7.5: Planet Mercury
7.8: Earth’s Moon
7.12: Martian Moons
9.17: A Comet Impacts a Planet

creation

15: Cosmology
15.1: What do you think?
15.2: In the beginning…
15.12: Religious or Philosophical Cosmology
15.13: Views on Creation

crescent

3.5: The Moon in our Skies

critical density

15.11: Questions Regarding the Eventual Fate of the Universe

cyanogen gas

9.16: Halley’s Comet

cycle

10: The Sun

D

damage

9.10: The Impact of Meteorites

Daoism

15.13: Views on Creation

dark energy

15.11: Questions Regarding the Eventual Fate of the Universe

dark matter

13: Galaxies
15.7: Recent Data on the Universe
15.11: Questions Regarding the Eventual Fate of the Universe

DarkMatter

13.2: Galaxies
13.16: Dark Matter
13.17: WIMPs and String Theory

dataCollection

15.10: What is Next for the Big Bang Theory?

daylight

3.4: Seasons and Seasonal Changes

deep sky objects

13.3: The History of Studying Galaxies

Deimos

7.12: Martian Moons

Democritus

14.4: Milky Way Galaxy Research

dense

12.6: White Dwarf

density

12.2: Stellar Birth

dependence

10.1: What do you think?

deuterium

10.5: A “Quick Guide” to Solar Fusion—The Proton-Proton Cycle

diagram

11.10: Stellar Distances

diamond ring

3.6: Eclipses

digital camera

5.6: Images from the Telescope

directions

3.2: Our Night Sky

discovery

6: Solar System Formation and Other Stellar Systems
8.9: Planet Uranus
8.10: Planet Neptune
9.20: Eris

diskshaped

13.8: Spiral Galaxies

distance

11.9: Distances to the Stars and other Celestial Objects
11.10: Stellar Distances
11.12: How Close are the Close-by Stars?
11.13: Light-Years
11.14: Parsec Vs. Light-Year Measurement
13: Galaxies

distance from sun

7.2: Comparing Planets

distances

1.3: Scale of the Cosmos
11: Stellar Properties

DistanceVelocity

13.5: Hubble’s Law

diurnalmotion

3.1: Motions of Objects

divination

9.14: Comets in History

DopplerEffect

4.5: Moving Objects, Spectra, and the Doppler Effect

DrGeoffMarcy

6.7: The Discovery of Extrasolar Planets

Dunn Solar Telescope

10.10: The National Solar Observatory

dust

12.7: Planetary Nebula

dust and gas

6.2: The Nebular Theory

dust storms

7.10: Snow on Mars

dwarf galaxies

13.15: Galactic Groups

dwarf planet

6.3: What is a Planet?

dwarf planets

6.4: The Nebular Theory - Other Important Evidence
9.4: Minor Bodies

DwarfPlanet

9.6: Brightest Asteroids Visible from Earth

dwarfplanets

9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud

Dysnomia

9.20: Eris

E

early telescopes

5: Telescope and Observing

early Universe

13.9: Irregular Galaxies

Earth

1.3: Scale of the Cosmos
2.5: The Wanderers
2.6: Claudius Ptolemy
2.7: Astronomy and Astrology
3.1: Motions of Objects
3.2: Our Night Sky
3.4: Seasons and Seasonal Changes
3.5: The Moon in our Skies
6.10: The Circumstellar Habitable Zone
7.1: What do you think?
7.7: Planet Earth
7.8: Earth’s Moon
7.9: Planet Mars
7.13: Characteristics of the Solar System’s Rocky Planets
9.8: Meteoroids, Meteors, and Meteorites
10.1: What do you think?
10.11: NASA’s Heliophysics Science Division
11.10: Stellar Distances
11.12: How Close are the Close-by Stars?
15.10: What is Next for the Big Bang Theory?

Earth maps

11.17: Celestial cartography

Earth orbit

5.9: Space-based Telescope

Earth Position

14: The Milky Way Galaxy

earth's moon

7: The Rocky Planets

east

3.2: Our Night Sky

eclipse

3.6: Eclipses
10.8: Studying the Sun

eclipse cycles

2.2: What Time Is It?

eclipses

3: Motions of the Moon, Sun, and Stars

Eclipsing Binary Star

11.24: Types of Star Systems and Stars

Ecliptic

3.3: The Sun and the Moon

Edmund Halley

9.15: Scientific Advances

Edwin Hubble

13.6: Classification of Galaxies
13.18: Gravitational Lensing
14.7: Andromeda Galaxy

EdwinHubble

13.4: Hubble’s Major Contributions

Einstein

13.18: Gravitational Lensing

electric power grid

10.9: The Dark Side of the Sun

electromagnetic

12.14: Gamma-Ray Bursts (GRBs)

electromagnetic radiation

4.3: The Electromagnetic Spectrum
12.11: Neutron stars

electromagnetic spectrum

4.3: The Electromagnetic Spectrum
5.4: Telescope Optical Types

ElectromagneticForce

15.5: The Planck Era

ElectromagneticForces

13.17: WIMPs and String Theory

electromagneticSpectrum

4.5: Moving Objects, Spectra, and the Doppler Effect

elements

4.4: Spectra

elliptical

13: Galaxies

elliptical galaxies

13.6: Classification of Galaxies
13.9: Irregular Galaxies
13.14: The Ages of Galaxies and What that Reveals

elliptical orbits

2.9: Observations of Motion- Brahe, Kepler, and Galilei

ellipticalgalaxies

13.7: Elliptical Galaxies

emission line spectrum

4.4: Spectra

Encarta Dictionary

15.12: Religious or Philosophical Cosmology

Enceladus

8.8: Saturn’s Satellites

Endeavour

5.10: Hubble Space Telescope

energy

10.2: Fission and Fusion
10.4: How the Sun Works
10.5: A “Quick Guide” to Solar Fusion—The Proton-Proton Cycle
13.12: Blazars- Quasar-like Object

energy bursts

12.12: Neutron Star and Companion Star Scenario

energy output

10.3: Our Star, the Sun
11.7: The Unknown in Astronomy

energy release

12.10: High-Mass Stars

energy transport

10.6: Solar Regions

environmental

5.8: Light Pollution

epicycles

2.6: Claudius Ptolemy

equatorial

5.5: Telescope Mounts

equinox

3.4: Seasons and Seasonal Changes

Eras

15.4: The Big Bang in Eras

Eris

6.3: What is a Planet?
9.20: Eris

Eros

9.6: Brightest Asteroids Visible from Earth

erosion

7.6: Planet Venus

ESA

13.9: Irregular Galaxies

ESO

12.4: Stellar Evolution

Europa

8.5: Jupiter’s Satellites

European Southern Observatory

12.4: Stellar Evolution

event horizon

12.13: High-Mass Star Stellar Endings

events

15.1: What do you think?

evidence

6: Solar System Formation and Other Stellar Systems
15: Cosmology
15.1: What do you think?

evolution

15.2: In the beginning…

evolutionary behavior

11.8: Star and Celestial Object Characteristics

existence

15.12: Religious or Philosophical Cosmology

exoplanets

6.6: Systems and Extrasolar Planets
6.7: The Discovery of Extrasolar Planets
6.8: The Kepler Mission
6.10: The Circumstellar Habitable Zone
6.11: Some Interesting Exoplanets
6.12: Extrasolar Planets
7.3: Rocky Planets

ExpandingUniverse

13.5: Hubble’s Law

expansion

13.13: Galaxies, Distance, and Age
13.16: Dark Matter
15.3: Physical Cosmology
15.6: Big Bang Evidence
15.11: Questions Regarding the Eventual Fate of the Universe

exploration

14.10: A Spinning Spiral
15.1: What do you think?

explosions

12.14: Gamma-Ray Bursts (GRBs)

extrasolarplanets

6.6: Systems and Extrasolar Planets

extraterrestrial

5.9: Space-based Telescope

extremophiles

6.10: The Circumstellar Habitable Zone

eyepiece

5.1: The Telescope
5.4: Telescope Optical Types

G

galactic clusters

13.18: Gravitational Lensing

galactic distance

13.13: Galaxies, Distance, and Age

galactic distance indicator

11.3: Cepheids

galactic types

13.9: Irregular Galaxies

GalacticCenter

14.3: Milky Way Galaxy Satellites

Galaxies

1.1: Module Introduction
1.2: Basic Objects in the Universe
12.14: Gamma-Ray Bursts (GRBs)
13: Galaxies
13.1: What do you think?
13.3: The History of Studying Galaxies
13.4: Hubble’s Major Contributions
13.6: Classification of Galaxies
13.7: Elliptical Galaxies
13.8: Spiral Galaxies
13.9: Irregular Galaxies
13.13: Galaxies, Distance, and Age
13.15: Galactic Groups
15.3: Physical Cosmology
15.4: The Big Bang in Eras

Galaxy

11.13: Light-Years
12.9: Nova, Novae, and Supernova
12.10: High-Mass Stars
13.2: Galaxies
13.16: Dark Matter
14: The Milky Way Galaxy
14.2: The Milky Way — Our Home Galaxy
14.3: Milky Way Galaxy Satellites
14.8: X-Ray and Gamma-Ray of the Milky Way Galaxy
14.10: A Spinning Spiral

galaxy evolution

13.6: Classification of Galaxies

galaxy formation

13.14: The Ages of Galaxies and What that Reveals

galaxy groups

13.15: Galactic Groups

galaxy research

14.7: Andromeda Galaxy

GalaxyCenter

14.9: Earth’s Position within the Milky Way Galaxy

galaxyclassification

13.7: Elliptical Galaxies

galaxycollision

13.11: Quasar-stellar Objects

galaxytypes

13.8: Spiral Galaxies

Galilean Satellites

5.3: Telescopic Observations
8.5: Jupiter’s Satellites

Galilei

2: Historical Astronomy

Galileo

2.8: The Birth of Modern Astronomy
2.10: Observations of the Heavens- Galileo
5.2: Early Telescopes
5.3: Telescopic Observations
14.5: Galileo Galilei, First to See the Milky Way Galaxy

Galileo Galilei

8.7: Saturn’s Rings
14: The Milky Way Galaxy

gamma

5.7: Space-Based Telescopes

gamma rays

12.11: Neutron stars

gammaRay

15.10: What is Next for the Big Bang Theory?

Ganymede

8.5: Jupiter’s Satellites

gas

12.2: Stellar Birth
12.7: Planetary Nebula

gas giant

8.4: Planet Jupiter

gas giant planets

8: The Gas Giant Planets

Gas Giants

6.4: The Nebular Theory - Other Important Evidence
6.12: Extrasolar Planets
7.2: Comparing Planets
7.3: Rocky Planets
8.1: What do you think?
8.6: Planet Saturn
8.11: Gas Giant Planets and Select Satellites Overviews
9.18: The Centaurs- Are they Asteroids or Comets?

gasdustdiscs

6.5: The Nebular Theory - Proplyds

gasgiants

8.2: Gas Giant Planets
8.3: Rings

General Theory of Relativity

13.18: Gravitational Lensing

Geocentric

2.6: Claudius Ptolemy
2.8: The Birth of Modern Astronomy

geology

7.5: Planet Mercury
7.7: Planet Earth

geospace

10.11: NASA’s Heliophysics Science Division

geysers

8.8: Saturn’s Satellites

Giant Impact Theory

7.8: Earth’s Moon

Giants

11.23: The Four Hertzsprung-Russell Diagram Stellar Groups

gibbous

3.5: The Moon in our Skies

Giotto

9.16: Halley’s Comet

Giovanni Cassini

8.7: Saturn’s Rings

Giovanni Schiaparelli

7.11: A Martian Controversy

Gliese 229B

6.12: Extrasolar Planets

Gliese 581

6.11: Some Interesting Exoplanets

global climate

10.9: The Dark Side of the Sun

globular clusters

11.5: Star Clusters
13.14: The Ages of Galaxies and What that Reveals

Goldilocks

6.10: The Circumstellar Habitable Zone

GPS

5.5: Telescope Mounts

GrandUnificationTheory

15.5: The Planck Era

granulation

10.7: Major Solar Features

graphPlotting

11.22: The Hertzsprung-Russell Diagram

gravitational

13.2: Galaxies

gravitational binding

11.5: Star Clusters

gravitational influence

2.7: Astronomy and Astrology

gravitational lensing

12.13: High-Mass Star Stellar Endings
13.18: Gravitational Lensing

GravitationalEffects

13.16: Dark Matter

GravitationalForce

2.11: The Mathematical Finish- Newton

gravitationalforces

13.17: WIMPs and String Theory
14.6: The Milky Way Galaxy’s Shape

gravitationally bound

13.15: Galactic Groups

Gravity

6.3: What is a Planet?
8.3: Rings
12.6: White Dwarf
15.5: The Planck Era

GRB

12.14: Gamma-Ray Bursts (GRBs)

Great Dark Spot

8.10: Planet Neptune

Great Red Spot

8.4: Planet Jupiter

Greek

2.5: The Wanderers

H

H.G. Wells

7.11: A Martian Controversy

habitable

6: Solar System Formation and Other Stellar Systems
6.10: The Circumstellar Habitable Zone

habitable zone

7.7: Planet Earth

Hades

9.19: Pluto

Halley’s Comet

9.14: Comets in History
9.15: Scientific Advances

Halley's Comet

9.16: Halley’s Comet

HarlowShapley

13.5: Hubble’s Law

Harvard University

11.19: Star Colors

HD80606b

6.11: Some Interesting Exoplanets

heavens

14.1: What do you think?

Heber Curtis

14.7: Andromeda Galaxy

heliocentric

2.8: The Birth of Modern Astronomy
2.10: Observations of the Heavens- Galileo

Heliocentric Solar System

2.9: Observations of Motion- Brahe, Kepler, and Galilei

Heliophysics

10.11: NASA’s Heliophysics Science Division

heliosphere

10.11: NASA’s Heliophysics Science Division

Helium

8.6: Planet Saturn
10.5: A “Quick Guide” to Solar Fusion—The Proton-Proton Cycle
12.1: Star Life
12.5: Low-Mass Stars
12.6: White Dwarf
13.14: The Ages of Galaxies and What that Reveals
15.6: Big Bang Evidence

HertzsprungRussell

11.23: The Four Hertzsprung-Russell Diagram Stellar Groups

HertzsprungRussellDiagram

11.22: The Hertzsprung-Russell Diagram

high pressure

7.6: Planet Venus

Hinduism

15.13: Views on Creation

Hipparchus

11.16: Magnitude System

historical

1.4: The Constellations

historical records

2.4: Contributions to Science
9.16: Halley’s Comet

history

2.10: Observations of the Heavens- Galileo
5.2: Early Telescopes
7.11: A Martian Controversy
9.3: What do you think?
9.14: Comets in History
14.4: Milky Way Galaxy Research
14.5: Galileo Galilei, First to See the Milky Way Galaxy

history of cartography

11.17: Celestial cartography

historyofscience

14.6: The Milky Way Galaxy’s Shape

Hoag’s Object

13.10: Active Galaxies

hostgalaxy

13.12: Blazars- Quasar-like Object

HRDiagram

11.22: The Hertzsprung-Russell Diagram
11.23: The Four Hertzsprung-Russell Diagram Stellar Groups

HST

5.10: Hubble Space Telescope

Hubble

5.7: Space-Based Telescopes
13: Galaxies
13.9: Irregular Galaxies
13.11: Quasar-stellar Objects

Hubble Constant

13.13: Galaxies, Distance, and Age

Hubble Galactic Tuning Fork

13.6: Classification of Galaxies

Hubble Sequence

13.6: Classification of Galaxies

Hubble Space Telescope

5: Telescope and Observing
5.9: Space-based Telescope
9.17: A Comet Impacts a Planet
13.3: The History of Studying Galaxies

Hubble's Law

13.13: Galaxies, Distance, and Age

HubbleGalacticTuningFork

13.4: Hubble’s Major Contributions

HubbleLaw

13.5: Hubble’s Law

HubblesLaw

13.4: Hubble’s Major Contributions

HubbleSpaceTelescope

5.10: Hubble Space Telescope
6.5: The Nebular Theory - Proplyds
12.8: White Dwarfs and Neighbors
15.10: What is Next for the Big Bang Theory?

Hydrogen

8.6: Planet Saturn
12.1: Star Life
12.5: Low-Mass Stars
13.14: The Ages of Galaxies and What that Reveals
15.6: Big Bang Evidence

hypothesis

2.1: The Study of Science

I

IAU

9.20: Eris

ice

7.9: Planet Mars
7.10: Snow on Mars
8.7: Saturn’s Rings

Ice Giant

8.9: Planet Uranus
8.10: Planet Neptune

icyBodies

9.2: The Oort Cloud and Kuiper Belt

image viewing

5.6: Images from the Telescope

images

5: Telescope and Observing
5.10: Hubble Space Telescope

ImmanuelKant

14.6: The Milky Way Galaxy’s Shape

impact

7.4: Craters
9.17: A Comet Impacts a Planet

Impact Craters

7.6: Planet Venus
7.10: Snow on Mars
7.13: Characteristics of the Solar System’s Rocky Planets

impact hazard

9.7: Asteroid Classification

impacts

9.10: The Impact of Meteorites

incandescent

4.2: Thermal Radiation

Inflation

15.5: The Planck Era

infrared

4.3: The Electromagnetic Spectrum
5.4: Telescope Optical Types
5.7: Space-Based Telescopes
15.10: What is Next for the Big Bang Theory?

InfraredObserving

14.3: Milky Way Galaxy Satellites

infraredRadiation

4.5: Moving Objects, Spectra, and the Doppler Effect

instruments

5.1: The Telescope

intelligent life

6.9: What We Have Learned about Stellar Systems and Extrasolar Planets?

interactive

InfoPage

intergalactic gas

13.14: The Ages of Galaxies and What that Reveals

interstellar cloud

6.2: The Nebular Theory

interstellar medium

12.1: Star Life
12.2: Stellar Birth

InterstellarMedium

13.2: Galaxies
14.9: Earth’s Position within the Milky Way Galaxy

introduction

3: Motions of the Moon, Sun, and Stars
6: Solar System Formation and Other Stellar Systems
9: Minor Bodies of the Solar System
10: The Sun
11: Stellar Properties

invention

5.2: Early Telescopes

Inverse Square Law

11.3: Cepheids
11.15: Stellar and Celestial Object Brightness

Io

8.5: Jupiter’s Satellites

ionosphere

10.11: NASA’s Heliophysics Science Division

Iris

9.6: Brightest Asteroids Visible from Earth

iron

9.9: Meteorites

iron meteorites

9.9: Meteorites

irregular

13: Galaxies

irregular galaxies

13.6: Classification of Galaxies
13.9: Irregular Galaxies

Isaac Newton

9.15: Scientific Advances

IsaacNewton

2.11: The Mathematical Finish- Newton

Islam

15.13: Views on Creation

Islamic contributions

2.4: Contributions to Science

isotopes

10.2: Fission and Fusion

L

Large Magellanic Cloud

13.3: The History of Studying Galaxies

LargeMagellanicCloud

14.3: Milky Way Galaxy Satellites

latitude

3.2: Our Night Sky

launch

5.9: Space-based Telescope

Law of Universal Gravitation

9.15: Scientific Advances

LawsOfMotion

2.11: The Mathematical Finish- Newton

LED lamps

5.8: Light Pollution

legends

4.1: Looking at a rainbow, what do you see?

Lemaître

13.5: Hubble’s Law

lens

5.2: Early Telescopes

lenticularspiral

13.8: Spiral Galaxies

LibreTexts

InfoPage

life

6.10: The Circumstellar Habitable Zone
6.11: Some Interesting Exoplanets
10.1: What do you think?
12.3: Stellar Mass

light

4.1: Looking at a rainbow, what do you see?
4.5: Moving Objects, Spectra, and the Doppler Effect
5.1: The Telescope
5.3: Telescopic Observations
11.24: Types of Star Systems and Stars

light bending

13.18: Gravitational Lensing

light bulbs

11.15: Stellar and Celestial Object Brightness

light measurement

5.6: Images from the Telescope

light pollution

5: Telescope and Observing
5.8: Light Pollution
14.1: What do you think?

lightning

8.4: Planet Jupiter

lightyear

11.14: Parsec Vs. Light-Year Measurement

Lipperhey

5.2: Early Telescopes

Little Dipper

1.5: Other Patterns

Local Group

13.15: Galactic Groups

LocalGroup

14.2: The Milky Way — Our Home Galaxy

logic

2.1: The Study of Science

longitude

3.2: Our Night Sky

longPeriodComets

9.2: The Oort Cloud and Kuiper Belt

Lowell Observatory

7.11: A Martian Controversy
9.19: Pluto

lowmassstars

12.5: Low-Mass Stars

lullabies

11.1: Module Introduction

luminosity

11.2: Variable Stars
11.3: Cepheids
11.8: Star and Celestial Object Characteristics
11.15: Stellar and Celestial Object Brightness
11.23: The Four Hertzsprung-Russell Diagram Stellar Groups
13.13: Galaxies, Distance, and Age

luminousobjects

13.11: Quasar-stellar Objects

lunar

3.5: The Moon in our Skies
7.8: Earth’s Moon

lunar calendars

2.2: What Time Is It?

lunar eclipse

3.6: Eclipses

lunar meteorites

9.9: Meteorites

lunar phases

2.2: What Time Is It?

M

M82

13.10: Active Galaxies

magnetic field

8.4: Planet Jupiter
10.6: Solar Regions

magnification

5.2: Early Telescopes
5.6: Images from the Telescope

magnitude

11.16: Magnitude System
11.18: Planispheres

Main Asteroid Belt

9.7: Asteroid Classification

MainSequence

11.23: The Four Hertzsprung-Russell Diagram Stellar Groups

maps

11.18: Planispheres

mars

1.3: Scale of the Cosmos
2.5: The Wanderers
7.1: What do you think?
7.9: Planet Mars
7.10: Snow on Mars
7.11: A Martian Controversy
7.12: Martian Moons
7.13: Characteristics of the Solar System’s Rocky Planets
8.3: Rings
9.5: Asteroids
10.1: What do you think?

Martian canals

7.11: A Martian Controversy

Martian meteorites

9.9: Meteorites

mass

6.3: What is a Planet?
12.3: Stellar Mass
12.13: High-Mass Star Stellar Endings
13.16: Dark Matter
14.10: A Spinning Spiral

massive objects

13.18: Gravitational Lensing

massive stars

10.5: A “Quick Guide” to Solar Fusion—The Proton-Proton Cycle
11.3: Cepheids
12.11: Neutron stars

mathematical prediction

8.10: Planet Neptune

Mathematics

2.11: The Mathematical Finish- Newton

matter composition

15.7: Recent Data on the Universe

matter transfer

11.4: Cataclysmic Variables

Mayan observatory

2.3: Ancient Observations

measurement

11.9: Distances to the Stars and other Celestial Objects
11.13: Light-Years

measurements

3.3: The Sun and the Moon
11.11: Everything is Moving
11.14: Parsec Vs. Light-Year Measurement

Mercury

1.3: Scale of the Cosmos
2.5: The Wanderers
7.1: What do you think?
7.5: Planet Mercury
7.13: Characteristics of the Solar System’s Rocky Planets

Messier Objects

13.3: The History of Studying Galaxies

meteor shower

9.12: Comet Characteristics

meteor showers

2.3: Ancient Observations
9.8: Meteoroids, Meteors, and Meteorites

meteorite recovery

9.10: The Impact of Meteorites

meteorites

6.1: Our Solar System
6.4: The Nebular Theory - Other Important Evidence
9.8: Meteoroids, Meteors, and Meteorites
9.9: Meteorites
9.10: The Impact of Meteorites

meteoroids

9.4: Minor Bodies
9.8: Meteoroids, Meteors, and Meteorites

meteors

9.8: Meteoroids, Meteors, and Meteorites
9.17: A Comet Impacts a Planet

methane

8.8: Saturn’s Satellites
8.9: Planet Uranus

microlensing

13.18: Gravitational Lensing

microprocessor

5.5: Telescope Mounts

Mike Reynolds

11.12: How Close are the Close-by Stars?

MikeBrown

9.20: Eris

Milky Way

5.8: Light Pollution
6.10: The Circumstellar Habitable Zone
11.13: Light-Years
13.3: The History of Studying Galaxies
13.14: The Ages of Galaxies and What that Reveals
13.15: Galactic Groups
14: The Milky Way Galaxy
14.1: What do you think?
14.5: Galileo Galilei, First to See the Milky Way Galaxy

Milky Way Galaxy

14.7: Andromeda Galaxy

MilkyWay

13.2: Galaxies
13.4: Hubble’s Major Contributions
13.16: Dark Matter
14.2: The Milky Way — Our Home Galaxy
14.3: Milky Way Galaxy Satellites
14.4: Milky Way Galaxy Research
14.8: X-Ray and Gamma-Ray of the Milky Way Galaxy
14.9: Earth’s Position within the Milky Way Galaxy
14.10: A Spinning Spiral

MilkyWayGalaxy

14.6: The Milky Way Galaxy’s Shape

minor

9: Minor Bodies of the Solar System

minor bodies

7.4: Craters
9.4: Minor Bodies

minor planets

9.4: Minor Bodies
9.5: Asteroids

misconception

10.4: How the Sun Works

misconceptions

13.1: What do you think?

mission

6: Solar System Formation and Other Stellar Systems

MIT

13.5: Hubble’s Law

mnemonics

11.21: Sample Spectral Types

module introduction

7: The Rocky Planets

molecules

4.4: Spectra

MOND

15.9: Beyond the Big Bang

Moon

1.3: Scale of the Cosmos
2.7: Astronomy and Astrology
3: Motions of the Moon, Sun, and Stars
3.3: The Sun and the Moon
3.5: The Moon in our Skies
7.7: Planet Earth
7.8: Earth’s Moon
7.13: Characteristics of the Solar System’s Rocky Planets
9.19: Pluto
9.20: Eris
11.16: Magnitude System

moons

1.2: Basic Objects in the Universe
5.3: Telescopic Observations
7.3: Rocky Planets
7.5: Planet Mercury
7.12: Martian Moons
8.2: Gas Giant Planets
8.5: Jupiter’s Satellites
8.8: Saturn’s Satellites
8.9: Planet Uranus
8.10: Planet Neptune
9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud

motion

2: Historical Astronomy
11.11: Everything is Moving

Motions

3: Motions of the Moon, Sun, and Stars

mount

5.5: Telescope Mounts

mounts

5: Telescope and Observing

MtWilsonObservatory

13.4: Hubble’s Major Contributions

multiple star systems

6.9: What We Have Learned about Stellar Systems and Extrasolar Planets?

multiverse

15.11: Questions Regarding the Eventual Fate of the Universe

myths

4.1: Looking at a rainbow, what do you see?

N

NASA

5.7: Space-Based Telescopes
5.10: Hubble Space Telescope
6.6: Systems and Extrasolar Planets
6.8: The Kepler Mission
7.1: What do you think?
7.5: Planet Mercury
7.6: Planet Venus
7.10: Snow on Mars
7.12: Martian Moons
8.4: Planet Jupiter
8.6: Planet Saturn
8.7: Saturn’s Rings
8.8: Saturn’s Satellites
8.10: Planet Neptune
9.6: Brightest Asteroids Visible from Earth
9.13: Images of Comets
9.17: A Comet Impacts a Planet
9.19: Pluto
10: The Sun
10.11: NASA’s Heliophysics Science Division
12.8: White Dwarfs and Neighbors
13.1: What do you think?
13.9: Irregular Galaxies

National Solar Observatory

10.10: The National Solar Observatory

nebula

6.2: The Nebular Theory
12.8: White Dwarfs and Neighbors

Nebulae

13.3: The History of Studying Galaxies
13.4: Hubble’s Major Contributions
14.2: The Milky Way — Our Home Galaxy

nebular theory

6.2: The Nebular Theory

nebulartheory

6.5: The Nebular Theory - Proplyds

NeilDeGrasseTyson

11.6: Consider this…

Neptune

1.3: Scale of the Cosmos
8: The Gas Giant Planets
8.1: What do you think?
8.10: Planet Neptune
8.11: Gas Giant Planets and Select Satellites Overviews

neutron star

12.10: High-Mass Stars
12.13: High-Mass Star Stellar Endings

neutron stars

12: Stellar Evolution
12.11: Neutron stars
12.12: Neutron Star and Companion Star Scenario

neutrons

10.2: Fission and Fusion

New Testament

2.4: Contributions to Science

Newton

2: Historical Astronomy

nickel

9.9: Meteorites

Night

3: Motions of the Moon, Sun, and Stars

night lighting

5.8: Light Pollution

night sky

13.1: What do you think?

normality

11.7: The Unknown in Astronomy

north

3.2: Our Night Sky

nova

12.8: White Dwarfs and Neighbors
12.9: Nova, Novae, and Supernova

novae

11.4: Cataclysmic Variables

nuclear

10.2: Fission and Fusion
12.14: Gamma-Ray Bursts (GRBs)

nuclear fusion

6.2: The Nebular Theory
10.6: Solar Regions
12.6: White Dwarf

Nucleosynthesis

15.4: The Big Bang in Eras

nursery

11.1: Module Introduction

P

Pallas

9.6: Brightest Asteroids Visible from Earth

parabolic orbits

9.15: Scientific Advances

parallax

9.15: Scientific Advances
11.10: Stellar Distances
11.14: Parsec Vs. Light-Year Measurement
14.4: Milky Way Galaxy Research

parsec

11.14: Parsec Vs. Light-Year Measurement

partial eclipse

3.6: Eclipses

ParticlePhysics

13.17: WIMPs and String Theory
15.4: The Big Bang in Eras

particles

4.3: The Electromagnetic Spectrum
8.7: Saturn’s Rings
10.2: Fission and Fusion
15.3: Physical Cosmology

penumbral eclipse

3.6: Eclipses

phases

3.5: The Moon in our Skies

phenomena

9.3: What do you think?

philosophical cosmology

15: Cosmology

philosophy

15.2: In the beginning…

Phobos

7.12: Martian Moons

Phoebe

9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud
9.18: The Centaurs- Are they Asteroids or Comets?

Phoenix Mars Lander

7.10: Snow on Mars

photographic comparison

11.5: Star Clusters

photometer

5.6: Images from the Telescope

photons

4.1: Looking at a rainbow, what do you see?
4.3: The Electromagnetic Spectrum
4.4: Spectra

photosphere

10.3: Our Star, the Sun
10.4: How the Sun Works
10.7: Major Solar Features
11.20: Spectral Type

photosphereTemperature

11.22: The Hertzsprung-Russell Diagram

physical characteristics

11.9: Distances to the Stars and other Celestial Objects

physical cosmology

15: Cosmology

physicalcosmologists

15.8: Issues with the Big Bang

Physics

2.10: Observations of the Heavens- Galileo
2.11: The Mathematical Finish- Newton
3.1: Motions of Objects
4.2: Thermal Radiation
13.16: Dark Matter
13.17: WIMPs and String Theory
15.4: The Big Bang in Eras

pitch

4.5: Moving Objects, Spectra, and the Doppler Effect

planet

2.5: The Wanderers
6.3: What is a Planet?
7.5: Planet Mercury
7.6: Planet Venus
8.9: Planet Uranus
8.10: Planet Neptune
9.8: Meteoroids, Meteors, and Meteorites
9.19: Pluto

planet characteristics

7.2: Comparing Planets

planet earth

7: The Rocky Planets

planet mars

7: The Rocky Planets

planet mercury

7: The Rocky Planets

planet overview

8: The Gas Giant Planets

planet venus

7: The Rocky Planets

planetary formation

6.2: The Nebular Theory
7.8: Earth’s Moon

planetary motion

2.9: Observations of Motion- Brahe, Kepler, and Galilei

planetary nebula

12: Stellar Evolution
12.6: White Dwarf
12.7: Planetary Nebula

planetary science

7.12: Martian Moons
8.1: What do you think?
8.11: Gas Giant Planets and Select Satellites Overviews
9.5: Asteroids

planetformation

6.5: The Nebular Theory - Proplyds

planets

1.2: Basic Objects in the Universe
2.6: Claudius Ptolemy
2.7: Astronomy and Astrology
3.3: The Sun and the Moon
6.1: Our Solar System
6.4: The Nebular Theory - Other Important Evidence
6.8: The Kepler Mission
7.1: What do you think?
8.2: Gas Giant Planets
8.11: Gas Giant Planets and Select Satellites Overviews
10.11: NASA’s Heliophysics Science Division
14.8: X-Ray and Gamma-Ray of the Milky Way Galaxy

PlanetX

9.20: Eris

plasma

10.6: Solar Regions

plate tectonics

7.7: Planet Earth

Pleiades

1.5: Other Patterns

Pluto

6.3: What is a Planet?
9.19: Pluto

Plutoids

6.4: The Nebular Theory - Other Important Evidence

Pogson

11.16: Magnitude System

polar caps

7.9: Planet Mars
7.10: Snow on Mars

polar hexagon

8.6: Planet Saturn

Polaris

11.16: Magnitude System

political issues

9.14: Comets in History

Polynesian navigation

2.3: Ancient Observations

possible

10.1: What do you think?

Potentially Hazardous Asteroids

9.7: Asteroid Classification

power

4.2: Thermal Radiation

powerful

15.1: What do you think?

precession

3.4: Seasons and Seasonal Changes

pressure

12.2: Stellar Birth

prominences

10.7: Major Solar Features

proplyds

6.5: The Nebular Theory - Proplyds

protogalactic clouds

13.14: The Ages of Galaxies and What that Reveals

proton

10: The Sun

protonprotoncycle

12.5: Low-Mass Stars

protons

10.5: A “Quick Guide” to Solar Fusion—The Proton-Proton Cycle

protoplanetary disk

6.2: The Nebular Theory

protoplanetarydisk

8.3: Rings

protostar

6.2: The Nebular Theory
12.2: Stellar Birth

Proxima Centauri

10.3: Our Star, the Sun
11.9: Distances to the Stars and other Celestial Objects
11.12: How Close are the Close-by Stars?
11.13: Light-Years

Ptolemaic

2.8: The Birth of Modern Astronomy

Ptolemy

2: Historical Astronomy
2.6: Claudius Ptolemy

public domain

11.11: Everything is Moving
13.1: What do you think?

publicdomain

3.1: Motions of Objects
6.6: Systems and Extrasolar Planets
9.6: Brightest Asteroids Visible from Earth
9.13: Images of Comets
11.6: Consider this…

pulsars

12.11: Neutron stars

pulsating radio star

12.11: Neutron stars

pulsating variables

11.2: Variable Stars

pulsation period

11.3: Cepheids

R

radiant energy

4.3: The Electromagnetic Spectrum

radiation

12.14: Gamma-Ray Bursts (GRBs)
14.9: Earth’s Position within the Milky Way Galaxy

radiative zone

10.6: Solar Regions

radio galaxies

13.10: Active Galaxies

radio telescope

5.4: Telescope Optical Types

radio waves

4.3: The Electromagnetic Spectrum

radioactive

10.2: Fission and Fusion

RadioAstronomy

14.3: Milky Way Galaxy Satellites

rainbow

4.1: Looking at a rainbow, what do you see?

rays

7.4: Craters

reactions

10.5: A “Quick Guide” to Solar Fusion—The Proton-Proton Cycle

recent data

15: Cosmology

red dwarf star

6.11: Some Interesting Exoplanets

Red Planet

7.9: Planet Mars
7.11: A Martian Controversy

redgiantstar

12.5: Low-Mass Stars

redshift

4.5: Moving Objects, Spectra, and the Doppler Effect
13.11: Quasar-stellar Objects
15.6: Big Bang Evidence

reflecting

5.4: Telescope Optical Types

Reflecting Telescope

5.3: Telescopic Observations

ReflectingTelescope

2.11: The Mathematical Finish- Newton

reflection

5.1: The Telescope

refracting

5.2: Early Telescopes
5.4: Telescope Optical Types

refraction

5.1: The Telescope

religion

2.4: Contributions to Science
2.10: Observations of the Heavens- Galileo
15.2: In the beginning…

religious

15.13: Views on Creation

repair

5.10: Hubble Space Telescope

Research

14: The Milky Way Galaxy

resolution

10.10: The National Solar Observatory

retrograde motion

2.6: Claudius Ptolemy

revolution

3.1: Motions of Objects

revolution length

7.2: Comparing Planets

ringed planet

8.6: Planet Saturn

rings

8: The Gas Giant Planets
8.2: Gas Giant Planets
8.3: Rings
8.7: Saturn’s Rings

Rochelimit

8.3: Rings

rocket

5.9: Space-based Telescope

rocky core

8.4: Planet Jupiter

rocky planets

6.4: The Nebular Theory - Other Important Evidence
7: The Rocky Planets
7.2: Comparing Planets
7.3: Rocky Planets
7.13: Characteristics of the Solar System’s Rocky Planets
8.1: What do you think?
9.5: Asteroids

RockyPlanets

7.1: What do you think?
8.2: Gas Giant Planets

Roman mythology

9.19: Pluto

rotation

3.1: Motions of Objects
13.13: Galaxies, Distance, and Age
14.10: A Spinning Spiral

royalty

9.14: Comets in History

S

Sacramento Peak

10.10: The National Solar Observatory

Sagittarius A*

14.7: Andromeda Galaxy

SagittariusA

14.9: Earth’s Position within the Milky Way Galaxy

satellite galaxies

13.9: Irregular Galaxies

Satellites

8: The Gas Giant Planets
8.3: Rings
8.5: Jupiter’s Satellites
12.14: Gamma-Ray Bursts (GRBs)
14: The Milky Way Galaxy
14.3: Milky Way Galaxy Satellites

Saturn

2.5: The Wanderers
8: The Gas Giant Planets
8.1: What do you think?
8.6: Planet Saturn
8.7: Saturn’s Rings
8.8: Saturn’s Satellites
8.11: Gas Giant Planets and Select Satellites Overviews

scientific evidence

2.7: Astronomy and Astrology

scientific method

2.1: The Study of Science

scientific mind

11.17: Celestial cartography

scientific principles

2.4: Contributions to Science

scientific revelation

9.16: Halley’s Comet

scientificDebate

15.9: Beyond the Big Bang

ScientificResearch

13.5: Hubble’s Law

scientifictheory

15.8: Issues with the Big Bang

Scorpius

6.9: What We Have Learned about Stellar Systems and Extrasolar Planets?

seasons

3: Motions of the Moon, Sun, and Stars
3.4: Seasons and Seasonal Changes

secondary star

11.4: Cataclysmic Variables

Seyfert galaxies

13.10: Active Galaxies

Shape

14: The Milky Way Galaxy

shapeandsize

13.7: Elliptical Galaxies

shooting stars

9.8: Meteoroids, Meteors, and Meteorites

Sidereus Nuncius

14.5: Galileo Galilei, First to See the Milky Way Galaxy

silicates

9.9: Meteorites
9.12: Comet Characteristics

Sir Isaac Newton

5.3: Telescopic Observations

Sir William Herschel

8.9: Planet Uranus

Sirius

11.16: Magnitude System
11.19: Star Colors

size

12.8: White Dwarfs and Neighbors

skepticism

2.1: The Study of Science

sky

3: Motions of the Moon, Sun, and Stars
9.3: What do you think?

SmallMagellanicCloud

14.3: Milky Way Galaxy Satellites

snow on mars

7: The Rocky Planets

sodium vapor lamps

5.8: Light Pollution

soerfm

9.13: Images of Comets

solar

6: Solar System Formation and Other Stellar Systems
10: The Sun
10.7: Major Solar Features
10.8: Studying the Sun

solar activity

10.9: The Dark Side of the Sun

solar eclipse

3.6: Eclipses

solar filter

10.8: Studying the Sun

solar flares

10.7: Major Solar Features
10.9: The Dark Side of the Sun

Solar Fusion

10.5: A “Quick Guide” to Solar Fusion—The Proton-Proton Cycle

solar images

10.10: The National Solar Observatory

solar observation

10.10: The National Solar Observatory

solar output

11.15: Stellar and Celestial Object Brightness

solar storms

10.9: The Dark Side of the Sun

Solar System

1.1: Module Introduction
1.2: Basic Objects in the Universe
1.3: Scale of the Cosmos
2.5: The Wanderers
2.6: Claudius Ptolemy
2.10: Observations of the Heavens- Galileo
6.1: Our Solar System
6.2: The Nebular Theory
6.3: What is a Planet?
6.4: The Nebular Theory - Other Important Evidence
6.6: Systems and Extrasolar Planets
6.12: Extrasolar Planets
7: The Rocky Planets
7.1: What do you think?
7.2: Comparing Planets
7.4: Craters
7.5: Planet Mercury
7.9: Planet Mars
8.1: What do you think?
8.4: Planet Jupiter
8.5: Jupiter’s Satellites
8.8: Saturn’s Satellites
8.9: Planet Uranus
8.11: Gas Giant Planets and Select Satellites Overviews
9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud
9.4: Minor Bodies
9.5: Asteroids
9.7: Asteroid Classification
9.9: Meteorites
9.12: Comet Characteristics
9.16: Halley’s Comet
9.19: Pluto
10.3: Our Star, the Sun
11.9: Distances to the Stars and other Celestial Objects
11.11: Everything is Moving

solar system formation

6.2: The Nebular Theory

solar wind

10.7: Major Solar Features

SolarSystem

2.8: The Birth of Modern Astronomy
6.5: The Nebular Theory - Proplyds
7.7: Planet Earth
8.2: Gas Giant Planets
9.2: The Oort Cloud and Kuiper Belt
14.6: The Milky Way Galaxy’s Shape
14.9: Earth’s Position within the Milky Way Galaxy
14.10: A Spinning Spiral

solid surfaces

7.3: Rocky Planets

solstice

3.4: Seasons and Seasonal Changes

solutions

5.8: Light Pollution

sound

4.5: Moving Objects, Spectra, and the Doppler Effect

south

3.2: Our Night Sky

space

3.1: Motions of Objects
5.7: Space-Based Telescopes
5.9: Space-based Telescope
6.7: The Discovery of Extrasolar Planets
6.8: The Kepler Mission
7.5: Planet Mercury
7.8: Earth’s Moon
7.12: Martian Moons
8.11: Gas Giant Planets and Select Satellites Overviews
9.8: Meteoroids, Meteors, and Meteorites
9.18: The Centaurs- Are they Asteroids or Comets?
12.14: Gamma-Ray Bursts (GRBs)
14.5: Galileo Galilei, First to See the Milky Way Galaxy
14.8: X-Ray and Gamma-Ray of the Milky Way Galaxy
14.9: Earth’s Position within the Milky Way Galaxy
14.10: A Spinning Spiral
15.8: Issues with the Big Bang
15.10: What is Next for the Big Bang Theory?

space debris

7.4: Craters

space exploration

1.1: Module Introduction
7.1: What do you think?
7.11: A Martian Controversy
8.5: Jupiter’s Satellites
9.11: Comets

spacecraft

7.9: Planet Mars
9.16: Halley’s Comet

spaceobservations

5.7: Space-Based Telescopes

spaceShuttle

5.10: Hubble Space Telescope

spectra

4.4: Spectra
4.5: Moving Objects, Spectra, and the Doppler Effect

spectral classes

11.8: Star and Celestial Object Characteristics

spectral type

11.19: Star Colors

spectral types

11.21: Sample Spectral Types

spectralType

11.20: Spectral Type
11.22: The Hertzsprung-Russell Diagram

spectroscopy

5.6: Images from the Telescope

spectrum

4.1: Looking at a rainbow, what do you see?
10.8: Studying the Sun

speed of light

11.13: Light-Years

speedoflight

13.12: Blazars- Quasar-like Object

SpeedOfSound

2.11: The Mathematical Finish- Newton

spiral

13: Galaxies

spiral galaxies

13.6: Classification of Galaxies
13.9: Irregular Galaxies

spiralarms

13.8: Spiral Galaxies

spiralgalaxies

13.8: Spiral Galaxies

SpiralGalaxy

14.2: The Milky Way — Our Home Galaxy

spiralgalleries

6.5: The Nebular Theory - Proplyds

spirituality

14.1: What do you think?

standard candle

12.9: Nova, Novae, and Supernova

star

11.1: Module Introduction
11.10: Stellar Distances
11.18: Planispheres
12.6: White Dwarf
12.8: White Dwarfs and Neighbors

star cartography

11.17: Celestial cartography

star characteristics

11.8: Star and Celestial Object Characteristics

star clusters

11.5: Star Clusters
13.3: The History of Studying Galaxies

star death

12.1: Star Life

star life

12: Stellar Evolution
12.4: Stellar Evolution

star maps

11.17: Celestial cartography

star names

2.4: Contributions to Science

star position

11.11: Everything is Moving

star study

10.3: Our Star, the Sun

star systems

11.24: Types of Star Systems and Stars

Starburst galaxies

13.10: Active Galaxies

starcounts

14.6: The Milky Way Galaxy’s Shape

stars

1.1: Module Introduction
1.2: Basic Objects in the Universe
1.4: The Constellations
1.5: Other Patterns
3.2: Our Night Sky
6.8: The Kepler Mission
10.9: The Dark Side of the Sun
11: Stellar Properties
11.5: Star Clusters
11.7: The Unknown in Astronomy
11.9: Distances to the Stars and other Celestial Objects
11.12: How Close are the Close-by Stars?
11.15: Stellar and Celestial Object Brightness
11.16: Magnitude System
11.19: Star Colors
11.20: Spectral Type
11.23: The Four Hertzsprung-Russell Diagram Stellar Groups
11.24: Types of Star Systems and Stars
12.1: Star Life
12.3: Stellar Mass
13.2: Galaxies
14.2: The Milky Way — Our Home Galaxy
14.4: Milky Way Galaxy Research
14.5: Galileo Galilei, First to See the Milky Way Galaxy
14.8: X-Ray and Gamma-Ray of the Milky Way Galaxy
14.9: Earth’s Position within the Milky Way Galaxy
15.3: Physical Cosmology

steady stars

11.7: The Unknown in Astronomy

SteadyState

15.9: Beyond the Big Bang

stellar

6: Solar System Formation and Other Stellar Systems
12.3: Stellar Mass
12.13: High-Mass Star Stellar Endings

stellar birth

12: Stellar Evolution
12.1: Star Life

stellar birth weight

12.3: Stellar Mass

stellar characteristics

11.1: Module Introduction

stellar color

13.14: The Ages of Galaxies and What that Reveals

stellar core

12.6: White Dwarf

stellar distances

11.14: Parsec Vs. Light-Year Measurement

stellar evolution

12: Stellar Evolution
12.1: Star Life
12.4: Stellar Evolution

stellar examples

11.21: Sample Spectral Types

stellar fuel

11.4: Cataclysmic Variables

stellar mass

11.8: Star and Celestial Object Characteristics
12: Stellar Evolution
12.4: Stellar Evolution

stellar nurseries

12.1: Star Life

stellar parallax

11.9: Distances to the Stars and other Celestial Objects

stellar size

11.8: Star and Celestial Object Characteristics

stellar structures

14.7: Andromeda Galaxy

stellar system

1.2: Basic Objects in the Universe
6.11: Some Interesting Exoplanets

stellar systems

6.6: Systems and Extrasolar Planets
6.9: What We Have Learned about Stellar Systems and Extrasolar Planets?
6.12: Extrasolar Planets

stellarevolution

11.22: The Hertzsprung-Russell Diagram
11.23: The Four Hertzsprung-Russell Diagram Stellar Groups
12.5: Low-Mass Stars

stellarformation

6.5: The Nebular Theory - Proplyds

stellarLuminosity

11.22: The Hertzsprung-Russell Diagram

stellarTemperature

11.22: The Hertzsprung-Russell Diagram

StephenColbert

11.6: Consider this…

stony meteorites

9.9: Meteorites

storms

8.6: Planet Saturn

street lighting

5.8: Light Pollution

StringTheory

13.17: WIMPs and String Theory

strong lensing

13.18: Gravitational Lensing

StrongForce

15.5: The Planck Era

StrongForces

13.17: WIMPs and String Theory

studying sun

10: The Sun

subgiantstar

12.5: Low-Mass Stars

sulfuric acid

7.6: Planet Venus

Sumerians

2.2: What Time Is It?

Sun

1.3: Scale of the Cosmos
2.6: Claudius Ptolemy
2.7: Astronomy and Astrology
3: Motions of the Moon, Sun, and Stars
3.1: Motions of Objects
3.3: The Sun and the Moon
3.4: Seasons and Seasonal Changes
6.1: Our Solar System
7.7: Planet Earth
10: The Sun
10.1: What do you think?
10.3: Our Star, the Sun
10.4: How the Sun Works
10.5: A “Quick Guide” to Solar Fusion—The Proton-Proton Cycle
10.6: Solar Regions
10.8: Studying the Sun
10.9: The Dark Side of the Sun
11.10: Stellar Distances
11.11: Everything is Moving
11.12: How Close are the Close-by Stars?
11.16: Magnitude System
12.5: Low-Mass Stars

Sun comparison

11.7: The Unknown in Astronomy

sunspots

2.10: Observations of the Heavens- Galileo
10.7: Major Solar Features
10.8: Studying the Sun

superclusters

13.15: Galactic Groups

Supergiants

11.23: The Four Hertzsprung-Russell Diagram Stellar Groups

supermassive black hole

14.7: Andromeda Galaxy

supermassiveBlackHole

13.11: Quasar-stellar Objects
14.9: Earth’s Position within the Milky Way Galaxy

supermassiveblackholes

13.2: Galaxies

supernova

12: Stellar Evolution
12.9: Nova, Novae, and Supernova
12.10: High-Mass Stars
12.11: Neutron stars
12.13: High-Mass Star Stellar Endings

supernovae

13.13: Galaxies, Distance, and Age
15.6: Big Bang Evidence

support structure

5.5: Telescope Mounts

surface temperature

11.8: Star and Celestial Object Characteristics

surface type

7.2: Comparing Planets

system

6: Solar System Formation and Other Stellar Systems

T

technology

6.7: The Discovery of Extrasolar Planets
15.2: In the beginning…
15.10: What is Next for the Big Bang Theory?

tectonic activity

7.3: Rocky Planets

telescope

2.10: Observations of the Heavens- Galileo
5: Telescope and Observing
5.1: The Telescope
5.2: Early Telescopes
5.4: Telescope Optical Types
5.5: Telescope Mounts
5.6: Images from the Telescope
5.7: Space-Based Telescopes
5.9: Space-based Telescope
5.10: Hubble Space Telescope
6.8: The Kepler Mission
10.3: Our Star, the Sun
10.10: The National Solar Observatory
14.5: Galileo Galilei, First to See the Milky Way Galaxy

telescopes

5.3: Telescopic Observations
11.24: Types of Star Systems and Stars

temperature

4.2: Thermal Radiation
7.5: Planet Mercury
7.8: Earth’s Moon
11.20: Spectral Type
12.2: Stellar Birth

temperature range

11.21: Sample Spectral Types

terrestrial planets

7.2: Comparing Planets
7.3: Rocky Planets

testing

2.1: The Study of Science

textbooks

InfoPage

theology

15.2: In the beginning…

theory

2.1: The Study of Science
6: Solar System Formation and Other Stellar Systems
15.3: Physical Cosmology

thermal energy

12.2: Stellar Birth

thermodynamics

15.11: Questions Regarding the Eventual Fate of the Universe
15.13: Views on Creation

thermonuclear fusion

10.2: Fission and Fusion

ThomasWright

14.6: The Milky Way Galaxy’s Shape

thunderstorms

8.4: Planet Jupiter

tidalforces

8.3: Rings

tides

2.7: Astronomy and Astrology

tilt

3.4: Seasons and Seasonal Changes

timekeeping

2.2: What Time Is It?

TiredLight

15.9: Beyond the Big Bang

Titan

8.8: Saturn’s Satellites

total eclipse

3.6: Eclipses

totality

3.6: Eclipses

transit

6.8: The Kepler Mission

transiting planets

6.11: Some Interesting Exoplanets

transneptunian

9: Minor Bodies of the Solar System

transneptunianobjects

9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud

trigonometry

11.10: Stellar Distances

triton

9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud

Trojan Asteroids

9.7: Asteroid Classification

Tunguska

9.10: The Impact of Meteorites

Twin QSO

13.18: Gravitational Lensing

Tycho Brahe

2.9: Observations of Motion- Brahe, Kepler, and Galilei
9.15: Scientific Advances

type 1a supernova

12.9: Nova, Novae, and Supernova

Y

young stars

11.5: Star Clusters
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