Earth, Moon and Sun in motion

For each effect you read about, write which bodies are involved, where each one stands, and which motion changes the picture from one day or year to the next.

Al-Battani later stayed for some time in Antioch, where he observed the solar eclipse of 23 January and the lunar eclipse of 2 August 901 ². In his Zij he describes the instruments he used: a tall gnomon divided into twelve parts; a celestial globe with five rings, apparently his own invention; a mural quadrant with a side of no less than a metre; and horizontal and vertical sundials to measure the seasonal hours ³.

In the Zij, al-Battani modestly says he follows Ptolemy's path while changing some of his elements on the strength of new observations, and that he wished to smooth the way for students of astronomy ⁴. He urges the observer to perseverance and care, saying that truth in celestial matters is reached only through the labours of many successive generations ³.

A new model of the Moon can be mistaken for a step towards a Sun-centred sky. The record on Ibn al-Shatir's lunar model says the achievement concerns a particular mathematical relationship, not invention of the Moon, all astronomy or heliocentrism ⁵, and that Earth remains central to the overall description ⁶.

Al-Battani measured the Sun's course over successive years, and al-Farghani explains an eclipse of the sun by the Moon's passing between the Sun and the Earth at conjunction. Why must someone who wants to say when eclipses fall follow the places of the Sun and the Moon for a long time, and not only on one day?

• Eclipses: how al-Farghani explains the moon's conjunction with the sun and its opposition to it.
• Al-Battani: his observations at al-Raqqa and Antioch.
• Al-Zij al-Sabi: his book and the instruments he describes.
• Ibn al-Shatir's lunar model: the problem of the Moon's changing distance.