astronomy

10 articles · All tags

• Julian vs Gregorian Calendar: Why the Change Happened
  The Gregorian calendar was adopted from 1582 because the Julian year ran about 11 minutes too long, leaving the dates about ten days out of step with the seasons.
• Why Does the Moon Have Phases? A Plain Explanation
  The Moon has phases because the Sun always lights half of it, and our view of that lit half changes as the Moon orbits Earth every 29.5 days, not Earth's shadow.
• Solar Eclipses: How They Work and Why Totality Is Rare
  A solar eclipse happens when the Moon passes between Earth and the Sun. Learn the types, why totality is rare, the Saros cycle, and how to watch one safely.
• Gravitational Waves: Ripples in Spacetime Explained
  Gravitational waves are ripples in spacetime from accelerating masses. LIGO first detected them in 2015 from two merging black holes 1.3 billion light-years away.
• Exoplanets
  Exoplanets explained: how astronomers find worlds around other stars, the strange planet types found so far, and the search for habitable Earth-like planets.
• The Antikythera Mechanism
  A geared bronze astronomical calculator from ancient Greece, recovered from a shipwreck in 1901 — the most complex mechanical device to survive antiquity.
• White Dwarfs
  The dense, cooling remnants of Sun-like stars supported by electron degeneracy pressure, with a maximum mass of about 1.4 solar masses.
• Kepler's Laws of Planetary Motion
  The three empirical laws describing planetary orbits: ellipses, equal areas in equal times, and the relation between period and orbit size.
• Black Holes
  Regions of spacetime where gravity is so strong that nothing, not even light, can escape from inside the event horizon.
• Stellar Nucleosynthesis
  How stars build chemical elements from hydrogen through nuclear fusion, and how explosions and stellar winds spread them into space.