1.1 Introduction

Astronomy dates from before written history. The rising and setting of the sun and the moon provided our early ancestors with a calendar to predict the seasons using shadows and sightings. Both agrarian and hunter-gatherer societies relied on what today are crude astronomical measurements to decide when and where to plant and hunt. The names of the constellations we see in the sky date from well before recorded history. The sundial, which measures time and season, is the oldest astronomical instrument and may have been invented before humans settled into social communities. Visual measurements of the positions of the sun, moon, planets, and stars appear in ancient texts. The Babylonians used these visual measurements as early as 3000 BC to predict with remarkable precision eclipses of the sun and the moon and the changing of the seasons. The Greek philosopher Eratosthenes of Cyrene (276-200 BC) used astronomical measurements to calculate the diameter of a spherical earth. Astronomical measurements were made and used by high priests and mystics in early society to curry favor from kings and emperors. The accurate prediction of solar and lunar eclipses became a politically powerful event used by kings and emperors to control societies.

1.2 Angle Measurements

Instruments for precise angle measurement using visual sighting along engraved scales advanced rapidly during the early Renaissance period. The increasing accuracy of position measurements of the planets, sun, and moon against the fixed stars across the sky over several years led Nicolas Copernicus in 1543, without the use of a telescope, to report that the sun was at the center of the solar system and that the Earth was the third planet. Using measurements made also without a telescope, Kepler discovered the laws that govern the motion of the planets around the sun and the satellites around a planet. It would take the invention of the optical telescope and its application to astronomical observation to make a great leap in our understanding of the physics of our solar system and the universe beyond.