# Foundations

## Overview: Historical Importance and Present-day Relevance

Astronomy is arguably the oldest science — every ancient civilization tracked the sky for
navigation, timekeeping, and agriculture long before anything resembling modern physics
existed. It remains directly relevant today, from GPS timing corrections rooted in general
relativity to the search for habitable worlds.

## Thought Experiment: Using Astronomy Knowledge to Survive on a Deserted Island

* **Celestial Navigation** — finding direction and latitude from the position of the Sun,
  Moon, and stars
* **Timekeeping** — the day, month, and year as astronomical periods (Earth's rotation,
  the Moon's orbit, Earth's revolution)
* **Harvesting Resources in Sync with Cycles and Seasons** — tides, seasons, and the
  agricultural calendar as consequences of orbital geometry

## Electromagnetic Spectrum

The full range of electromagnetic radiation — radio, microwave, infrared, visible,
ultraviolet, X-ray, and gamma-ray — each band probing different physical processes and
requiring different observing techniques (ground-based vs. space-based telescopes).

## Interaction of Light and Matter

* **Light as a Wave and Particle** — the wave–particle duality underlying spectroscopy and
  photon-counting detectors alike
* **Reflection, Refraction, and Diffraction** — the geometric-optics basis of every
  telescope design
* **Absorption and Emission** — atomic and molecular spectral lines as fingerprints of
  composition, temperature, and motion
* **Scattering, Interference, and Polarization** — from why the sky is blue to
  interferometric imaging

## Mapping the Sky

Celestial coordinate systems (equatorial, ecliptic, galactic), constellations as
historical sky maps, and the modern astrometric surveys that replaced them.