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Astronomy is one of the oldest sciences. Ancient Greek people used the positions of the stars to navigate, and to find when was the best time to plant crops. Astronomy is very similar to astrophysics. A related subject, cosmology, is concerned with studying the Universe as a whole, and the way the universe changed over time. Astronomy is not the same as astrology, the belief that motion of the stars and the planets may affect human lives. Early astronomers used only their eyes to look at the stars. They made maps of the constellations and stars for religious reasons and calendars to work out the time of year. Early civilisations such as the Mayan people of Central America and the Ancient Egyptians built simple observatories and drew maps of the stars positions. They also began to think about the place of Earth in the universe. For a long time people thought Earth was the centre of the universe, and that the planets, the stars and the sun went around it. This is known as geocentrism. Ancient Greeks tried to explain the motions of the sun and stars by taking measurements. A mathematician named Eratosthenes was the first who measured the size of the Earth and proved that the Earth is a sphere. A theory by another mathematician named Aristarchus was that the sun is in the centre and the Earth is moving around it. This is known as heliocentrism. Only a few people thought it was right. The rest continued to believe in the geocentric model. Most of the names of constellations and stars come from Greeks of that time. Arabic astronomers made many advancements during the Middle Ages including improved star maps and ways to estimate the size of the Earth. They also learned from the ancients by translating Greek books into Arabic. During the renaissance a priest named Nicolaus Copernicus thought, from looking at the way the planets moved, that the Earth was not the centre of everything. Based on previous works, he said that the Earth was a planet and all the planets moved around the sun. This brought back the old idea of heliocentrism. A physicist called Galileo Galilei built his own telescopes, and used them to look more closely at the stars and planets for the first time. He agreed with Copernicus. The Catholic Church thought Galileo was wrong. He spent the rest of his life under house arrest. Heliocentric ideas were soon improved by Johannes Kepler and Isaac Newton, who invented the theory of gravity.

After Galileo, people made better telescopes and used them to see farther objects such as the planets Uranus and Neptune. They also saw how stars were similar to our Sun, but in a range of colours and sizes. They also saw thousands of other faraway objects such as galaxies and nebulae.


Text adapted from Kids’ Wikipedia, which is in the public domain.


What was the general feeling about Aristarchus’ theory of the heliocentrism?