Explore the universe, from the first sky maps to gravitational waves
A complete knowledge framework for astronomy: history, observations, physical models, people, instruments and missions — designed to grow into an interactive online observatory.
Explore by field
Classical & Spherical Astronomy
How humans map the sky, measure time and predict apparent celestial motion.
22 topics02Astrometry & Celestial Mechanics
Precise positions, distances and gravitational motion of celestial bodies.
20 topics03Observational Astronomy
Observing the universe across the electromagnetic spectrum and extracting physical information.
18 topics04Solar Astronomy & Heliophysics
The Sun as a star and the plasma environment extending through the Solar System.
15 topics05Stellar Astrophysics
How stars form, shine, evolve, interact and end their lives.
26 topics06Planetary Science & Exoplanets
Worlds, moons and small bodies in our Solar System and around other stars.
27 topics07Interstellar Medium & Astrochemistry
Gas, dust, magnetic fields and chemistry between the stars.
14 topics08Galactic Astronomy
The structure, contents, dynamics and history of the Milky Way.
13 topics09Extragalactic Astronomy
Galaxies beyond the Milky Way, their active nuclei, groups and clusters.
18 topics10High-Energy & Compact Objects
Extreme gravity, dense matter, accretion and relativistic outflows.
19 topics11Cosmology
The origin, contents, geometry, evolution and large-scale structure of the universe.
30 topics12Gravitational & Multi-Messenger Astronomy
Observing the universe with gravitational waves, neutrinos, cosmic rays and combined messengers.
17 topics13Astrobiology & Search for Life
The origin, distribution and detectability of life in the universe.
13 topics14Computational, Survey & Data Astronomy
Numerical simulation, statistics, machine learning and large astronomical surveys.
17 topics15Astronomical Instrumentation & Space Astronomy
Telescopes, detectors, interferometers and spacecraft that turn photons and particles into measurements.
18 topics16History & Archaeoastronomy
How astronomical knowledge developed across cultures, instruments and scientific revolutions.
20 topicsA journey through astronomical history
Ancient sky cultures
Systematic naked-eye observation, calendars, constellations and eclipse records across early civilizations.
Medieval & Islamic astronomy
Preservation, refinement and extension of Greek, Indian, Chinese and Islamic astronomical traditions.
Renaissance revolution
Heliocentrism, telescopic astronomy and Keplerian planetary motion.
Classical celestial mechanics
Newtonian gravitation, orbit theory, precision positional astronomy and discovery by calculation.
Birth of astrophysics
Spectroscopy, photography, stellar classification and the physical study of stars.
Modern universe
Galaxies, expanding-universe cosmology, radio/X-ray astronomy, stellar evolution and compact objects.
Precision & multi-messenger era
Exoplanets, large surveys, precision cosmology, gravitational waves, neutrinos and event-horizon imaging.
Frontier astronomy
Quantum cosmology, dark sector, first stars, biosignatures and next-generation observatories.
Foundation topics
Constellations and star lore
A complete introduction to Constellations and star lore within Naked-eye sky, linking observations, physical models, history and modern applications.
Classical & Spherical AstronomyDaily motion of the sky
A complete introduction to Daily motion of the sky within Naked-eye sky, linking observations, physical models, history and modern applications.
Classical & Spherical AstronomySolstices and equinoxes
A complete introduction to Solstices and equinoxes within Naked-eye sky, linking observations, physical models, history and modern applications.
Classical & Spherical AstronomyLunar phases
A complete introduction to Lunar phases within Naked-eye sky, linking observations, physical models, history and modern applications.
Classical & Spherical AstronomySolar and lunar eclipses
A complete introduction to Solar and lunar eclipses within Naked-eye sky, linking observations, physical models, history and modern applications.
Classical & Spherical AstronomyPlanetary retrograde motion
A complete introduction to Planetary retrograde motion within Naked-eye sky, linking observations, physical models, history and modern applications.
Classical & Spherical AstronomyCelestial sphere
A complete introduction to Celestial sphere within Celestial sphere & coordinates, linking observations, physical models, history and modern applications.
Classical & Spherical AstronomyHorizon coordinate system
A complete introduction to Horizon coordinate system within Celestial sphere & coordinates, linking observations, physical models, history and modern applications.
Classical & Spherical AstronomyEquatorial coordinate system
A complete introduction to Equatorial coordinate system within Celestial sphere & coordinates, linking observations, physical models, history and modern applications.
Interactive astronomy labs
Celestial Sphere Explorer
Change observer latitude and sidereal angle to see how the celestial poles, horizon and a sample star move.
02Interactive labKepler Orbit Lab
Vary semimajor axis and eccentricity, then inspect periapsis, apoapsis and orbital period.
03Interactive labInteractive H–R Diagram
Explore representative stars by temperature and luminosity and connect position to radius and stellar class.
Study tools
Quizzes
Multiple-choice question banks across 48 core topics, from observational astronomy to cosmology.
Interactive games
Steer orbits, measure redshift, navigate the sky with Polaris.
Astronomy olympiads
IOAA, IAO, USAAAO and national olympiads — format and topics.
Open problems
Dark energy, dark matter, the Hubble tension and other unsolved questions.