Lodestar — space, explained in layers you choose to open

Lodestar: space, explained in layers you choose to openEvery topic is one page of seven layers, from a one-sentence hook, through an everyday analogy and a live simulation, down to the derivation and the open questions. The simulations need JavaScript; the topics are:

Black Holes: One number, how heavy, decides everything else about it.

Dark Matter: Stars at a galaxy’s edge orbit too fast for the matter we can see. Something unseen is pulling on them.

Escape Velocity: How fast you have to throw something so gravity never gets it back.

Exoplanets: A star dims by a hundredth, on schedule, and there is a world in the way.

Galaxies: Islands of hundreds of billions of stars. When two meet, their stars almost never touch, but gravity pulls both into new shapes.

Gravitational Waves: Two black holes fall together, and space itself rings.

Hawking Radiation: Black holes are not quite black. The small ones glow, shrink, and end in a flash.

Kepler Orbits: Why orbits are ellipses, why the star sits off-centre, and why speed changes.

Nebulae: A cloud of gas lit from inside by newborn stars glows the way a neon sign does: its atoms are driven to give off light in colours all their own.

Neutron Stars and Pulsars: A star’s collapsed core, heavier than the Sun and a city across, sweeping the sky with its beams.

Planetary Atmospheres: Whether a world keeps its air is a race between gravity and heat.

Scale of the Universe: Ten rungs from a proton to the observable universe, and the ratios between them.

Supernovae: How a star dies depends on one number, its mass. Above a line, it ends in the brightest event in its galaxy.

The Cosmic Distance Ladder: Almost every distance to a galaxy rests on a shorter one, all the way down to the width of Earth’s orbit.

The Cosmic Microwave Background: The oldest light there is still fills the sky, cooled by the stretching of space to three degrees above absolute zero.

The Early Universe: From a trillion-degree soup of quarks to the first atoms: what the universe was made of at every moment, and why it changed.

The Expansion of the Universe: Almost every galaxy is moving away from us, and the farther it is, the faster it goes.

The Habitable Zone: Around every star there is a ring where water can stay liquid. Being in it is where the question starts, not where it ends.

Tides: The Moon pulls harder on the near side of Earth than the far side. The oceans stretch both ways, and the sea rises twice a day.

Time Dilation: Moving clocks run slow, and so do clocks deep in gravity. It is the one kind of time travel physics is sure of.

Why the Sun Shines: The Sun is not hot enough for its protons to touch. They fuse anyway, and the reason is quantum.

Wormholes and White Holes: Einstein’s equations allow tunnels through space and black holes run backwards. Nothing we know of can build either.