Heliocodex

Learn / Ideas that run through all of it

Light, and how we know anything

One of the ideas that runs through every place the lessons go. 7 lessons, in the order to read them.

  1. Start hereLight is the only messengerNearly everything known about space arrived as light, and light always brings old news.First look · How it works
  2. The whole spectrum: light we cannot seeThe colours we see are a thin slice of light. Radio waves, infrared, ultraviolet, X-rays and gamma rays are the same thing at other wavelengths.First look · How it works
  3. Reading starlightSpread a star's light into a rainbow and it is crossed by dark lines. They tell you what the star is made of, how hot it is and how it is moving.First look · How it works
  4. TelescopesA telescope's first job is to collect light, not to magnify. Bigger mirrors see fainter and sharper, and that has driven four centuries of building.First look · How it works
  5. Messengers other than lightThree other things reach the Earth from deep space: neutrinos, cosmic rays and ripples in space itself. Each brings news that light cannot.First look · How it works
  6. Telescopes in spaceThe air blocks most kinds of light and blurs the rest. Lifting a telescope above it costs a fortune, and has changed what is known about almost everything.First look · How it works
  7. Redshift and the Doppler effectA siren drops in pitch as it passes you. Light does the same thing, and that small shift is how the speed of a star and the growth of the universe are measured.First look · How it works

Outline Still to be written here

  1. Radio astronomyThe sky in radio waves, from the first hiss to dishes the size of the Earth.
  2. The X-ray skyWhy X-ray telescopes must fly above the air, and what they find.