Pioneers

Programme Outline

Summary

1. How astronomy arose from the need to measure time. Using the motions of the heavens to keep track of the date, the season, when to sow, and when to prepare for winter. About 6000 years ago, the Babylonians charted celestial movements, grouped stars into patterns, and observed the 'wandering stars' (in reality the five nearest planets). The Chinese mapped the cosmos and recorded phenomena such as comets.
2. The Egyptians divided their year into 365 days; the Maya used a calendar of 584 days. The Greeks placed the Sun, Moon, five planets and background stars in crystal spheres surrounding the Earth. Eratosthenes demonstrated that the Earth is spherical, and Hipparchus mapped the sky, and worked out the relative distances of the Sun and Moon. Ptolemy believed the planets orbited Earth, and came up with a theory to fit his observations. He was wrong, but his ideas persisted for nearly 1500 years until Copernicus placed the Sun at the centre of our planetary system, and Johannes Kepler devised his three laws of planetary motion.
3. The beginnings of modern astronomy, as Galileo turned his telescope on the sky. Isaac Newton studied gravity, and optics, and improved the telescope. Later, William Herschel discovered Uranus, built the biggest reflecting telescope in the world, catalogued the stars, and recognised the shape of our galaxy. The Third Earl of Rosse built an even larger telescope and saw the spiral structure of galaxies.
4. The nineteenth century yielded two important tools: spectroscopy and photography. In the 1920s, Edwin Hubble used both to observe galaxies and the fact they moving further away. Beyond the visible spectrum, radio telescopes detect distant radio sources, and ever more powerful telescopes peer back towards the beginnings of space and time.

00.10 - 00.52 Introduction

• The need to measure time - to know the date, the season, when to sow, and when to prepare for winter.
• In ancient times, people used the motions of the heavens to tell the time and establish their calendars.

00.52 - 02.19 The birth of astronomy

• About 6000 years ago, the Babylonians charted celestial movements, grouped the stars into constellations, and imagined the signs of the Zodiac. The 'wandering stars' they saw we know as the five nearest planets.
• Meanwhile, Chinese astronomers mapped the cosmos, and carefully recorded phenomena such as comets.
• The Egyptians used the dawn rising of Sirius to foretell the annual flooding of the Nile. They believed heavenly cycles to be controlled by their gods, and they devised a 365-day calendar.
• Much later, in Central America, the Maya devised a 584-day calendar based on the cyclical movements of Venus.

02.19 - 04.55 Early ideas

• Various early ideas to explain the mechanics of the heavens, beginning with a Hindu view.
• The Greeks placed the Sun, Moon, five known planets, and background stars in a series of concentric crystal spheres around the Earth.
• In 200 BC, Eratosthenes showed that the Earth is spherical, and used geometry to work out its circumference.
• Hipparchus compiled the first star map, recorded the brightnesses of the stars, and worked out the relative distance to the Moon and Sun by observing eclipses.
• Ptolemy mistakenly believed that the planets orbit the Earth. He devised a complex system which fitted his observations - even the strange little 'reverses' made by some planets. His ideas persisted for almost 1500 years.

04.55 - 06.30 The Sun-centred system

• In the 16th century, a Polish cleric, Nicolaus Copernicus, reasons that the Earth and other planets orbit the Sun, with the Moon orbiting Earth. But he thinks the orbits are perfect circles.
• In the early seventeenth century, Johannes Kepler devised three laws of planetary motion.
• He used the precise observations of Tycho Brahe to show that the planets orbit the Sun in ellipses, not circles. He showed that a planet moves quickest when closest to the Sun and slowest when furthest away, and that the orbital periods of planets nearer to the Sun are shorter than those further away.
• Kepler correctly explained why some planets appear to make a backwards loop in the sky as they are overtaken by the Earth.

06.30 - 07.34 Important discoveries

• In the early seventeenth century, Galileo was the first to turn a telescope on the sky. He made many discoveries including craters on the Moon, moons around Jupiter, and spots on the Sun.
• Christiaan Huygens discovered Saturn's largest moon, and observes that the rings are detached from the planet. Giovanni Cassini discovered a gap in the rings, now known as the Cassini Division.
• Isaac Newton revolutionised astronomy, by working out the laws of gravity and optics, and shortening the telescope using mirrors.

07.34 - 09.50 To the beginnings of time and space

• In the eighteenth century, William Herschel discovered Uranus, built better reflecting telescopes, catalogued the stars, and recognised that our Galaxy is a flattened disk.
• In the mid-nineteenth century, the Third Earl of Rosse built an even larger telescope. He glimpsed galaxies beyond our own and sketched their spiral structure.
• The nineteenth century yielded two new tools for astronomy: spectroscopy (the analysis of light to work out the nature of objects in space) and photography.
• In the 1920s, Edwin Hubble used both tools to observe many galaxies, and discovered that they are all moving apart.
• Beyond the range of optical telescopes, radio telescopes see ever more distant objects.
• Today, increasingly powerful telescopes penetrate back towards the beginnings of time and space.