In order to understand the work of Muslim astronomers it is necessary to return to the beginning – not just to the early Egyptian and Babylonian stargazers – but to the first beginning of all: the Big Bang. It is only in the last fifty years or so that cosmologists and astrophysicists have come to an agreement about the origins of the universe. About fourteen billion years ago a hot, dense, primordial mix exploded, and the rapid expansion that followed led to the vast cosmic configuration that we find today. Cosmologists estimate that our universe contains approximately one hundred billion galaxies – our Milky Way is one. And each galaxy in turn contains about one hundred billion stars – our Sun, the centre of our solar system, is one. Formed about 4.6 billion years ago, our solar system includes planets, moons, dwarf planets, comets, meteors, and an asteroid belt. The Sun is the principal component of the solar system, containing 99.9 per cent of its mass and dominating its gravitational field. Eight planets orbit the Sun. In order they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Until 2006 Pluto, the farthest from the Sun, had also been listed as a planet but it has now been reclassified as a dwarf planet. The planets differ in size, mass, composition, temperature, and distance from the Sun. The inner planets (Mercury, Venus, Earth, and Mars) are relatively small, composed mostly of rock and have few or no moons. The outer planets (Jupiter, Saturn, Uranus, Neptune, and the dwarf Pluto) are massive, mostly gaseous, and have rings and moons. The Earth is the densest planet and Jupiter is the largest.

From the dawn of human history man has gazed at the heavens and wondered at the spectacle: the rising and setting of the Sun, the shifting phases of the Moon, the movements of the planets, and the patterns of the night-time stars. The Sun was probably the first celestial body to be studied. Its apparent annual motion on the ecliptic (the apparent path of the Sun on the celestial sphere) was always eastward, but not perfectly uniform.