Astrophysics

Stars, celestial phenomena, and cosmic distances

Kepler's Laws of Planetary Motion Explained: Ellipses, Equal Areas and the Harmony of the Worlds

18 Oct 2026

Kepler's laws of planetary motion explained with three interactives: draw a real orbit with pins and string, stamp equal areas, and weigh a black hole.

Kepler's lawsplanetary motionelliptical orbitseccentricityKepler's third laworbital periodhistory of astronomyexoplanetsSagittarius A*astrophysics

Escape Velocity Calculator: From Leaving Earth to Falling Into a Black Hole

4 Oct 2026

Escape velocity calculator for Earth, the Moon, Mars and the Sun, with an interactive black hole maker showing how compressed a mass must be to trap light.

escape velocityblack holesSchwarzschild radiusevent horizonNewton's cannonorbital velocityastrophysicsgeneral relativity

Newton's Law of Gravitation and Orbital Velocity Calculator

10 Aug 2026

Newton's law of gravitation calculator and orbital velocity simulator — find orbital speed, period via Kepler's third law, and explore elliptical orbits.

Newton's law of gravitationgravityorbital mechanicsKepler's third laworbital velocitycircular orbitelliptical orbitastrophysics

Stellar Distances

16 Aug 2018

How astronomers measure cosmic distances — parallax, Cepheids, and Hubble's Law.

astrophysicsparallaxdistance laddercosmology

What is a Lunar Eclipse?

2 Feb 2018

Penumbral, partial, and total eclipses — plus the rare Super Blue Blood Moon.

astrophysicsmooneclipseblood moon

What Are Shooting Stars?

23 Nov 2017

Meteoroids, meteors, and meteorites — space rocks burning up in Earth's atmosphere.

astrophysicsmeteorsmeteor showers