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How Stars Are Born, Live and Die
Follow a star from a cold gas cloud through fusion, red giant and supernova stages to a white dwarf, neutron star or black hole, and why mass decides its fate.
Universe and Matter
Stars and Galaxies
How stars live and die and how galaxies and the early universe are understood.
How Astronomers Measure Distances in Space
See how parallax, Cepheid variables and supernovae form a ladder of methods that lets astronomers measure distances from nearby stars to far-off galaxies.
How the Big Bang Theory Works
What the Big Bang model says about an expanding, cooling universe, the main evidence behind it, and the common misunderstandings about an explosion and a center.
Neutron Stars and Pulsars Explained
Learn how a collapsed stellar core becomes a city-sized neutron star, why some of them sweep beams of radio waves past Earth, and what pulsars reveal.
The Milky Way Galaxy Explained
Explore the shape, size and contents of the Milky Way, from its central bar and spiral arms to its halo, and find out where the Sun sits within it.
What Is a Black Hole and How Do We Know They Exist
A black hole is a region where gravity lets nothing escape. Learn how they form and the evidence from stellar orbits, X-rays, gravitational waves and images.
What Is a Light Year?
A light year is the distance light travels in one year, about 9.46 trillion kilometers. Learn why it measures distance, not time, and how it helps us gauge space.
What Is Dark Matter?
Dark matter is the unseen mass astronomers infer from galaxy rotation, gravitational lensing and the early universe. Learn the evidence and what is still unknown.
Why Do Stars Twinkle?
Stars twinkle because turbulent air bends their light as it passes through the atmosphere. Learn why planets shine more steadily and why stars in space do not twinkle.
Why the Constellations Change with the Seasons
Earth's yearly orbit changes which stars face our night side, so Orion rules winter evenings and Scorpius summer ones. See how it works and why some stars never leave.
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Our Universe Space, the solar system and how we picture the cosmos. Physics and Matter Modern physics, light, the elements and everyday math. Planets and Space Exploration Missions, the Moon, eclipses and the search for life beyond Earth. Forces, Energy and Motion Classical physics that explains everyday motion, heat, sound and electricity. Chemistry and Materials Reactions, everyday substances and how common materials are made.