![]() After discovering Uranus in 1781, William Herschel opened new areas of research in 1800 by discovering infrared radiation – a type of light that is not visible to the human eye. Over the following centuries, astronomers around the world formalized the study of the sky by creating detailed catalogues of stars, star clusters, and nebulae. ![]() In his honour, they are known as the Galilean moons. Italian astronomer Galileo Galilei popularized the use of telescopes to study and discover celestial objects, including Jupiter's four biggest moons. Their observations and investigations were strengthened by the invention of the telescope in the early 17th century. This progress dramatically improved humanity's understanding of the universe. The work of astronomers Tycho Brahe and Johannes Kepler led to an accurate description of planetary motions and laid the foundation for Isaac Newton's theory of gravitation. The new theory was one of many revolutionary ideas about astronomy that emerged during the Renaissance period. This model explained the unusual path of planets that astronomers had observed. In 1543, Polish astronomer Nicolaus Copernicus proposed a heliocentric model of the solar system in which the planets orbit the Sun. This is called retrograde motion and is one of the key pieces of evidence that the Sun lies at the centre of the solar system and all the planets revolve around it. Sometimes they appear to loop backwards for short periods of time. When we observe, from Earth, the planets around the Sun, they do not always appear to be moving in one direction in our sky. ![]() The first documented observation of the neighbouring Andromeda Galaxy was in the year 964 by a Persian astronomer who described it as a "nebulous smear." For centuries, it was simply known in star charts as the "Little Cloud." Before then, nearby galaxies were thought to be cloudy regions of the Milky Way. The notion that our own galaxy – the Milky Way – is but one of trillions of other galaxies in the universe only dates back about a century. Some supernovae are even bright enough to be visible during the day! Cloudy galaxies Several supernova explosions have been observed since then, including a particularly bright one in the year 1054, which (at its peak) was four times brighter than planet Venus, one of the brightest objects in the night sky. In the year 185, Chinese astronomers became the first to document a supernova. That is very close to the real value of 40,075 kilometres! Bright supernovae Taking into account the distance between those two locations and the difference in the lengths of the shadows, they calculated that Earth's circumference was about 46,250 kilometres. They did this by measuring the length of the shadow cast by an object at exactly the same time, in two different locations. These philosophers were even able to calculate the circumference of Earth quite accurately. They also observed the round shadow of Earth on the Moon during lunar eclipses. They noted that the night sky looked different when seen from various locations on Earth, hinting at our planet's curved surface. A spherical EarthĪs early as the 6th century BCE, ancient Greek philosophers documented evidence that Earth was a sphere. Historians and astronomers now believe the Babylonians were among the first to recognize the planets Mercury, Venus, Mars, Jupiter, and Saturn, which become visible to the naked eye at different times of the year. They concluded that something fundamentally different existed: these five points of light were not stars at all. Some examples of early discoveries include: Planets versus starsīabylonian astronomers in the first and second millennia BCE tracked five points of light in the night sky that moved differently than the other stars did. Historical records include many star charts, which reveal clear efforts to map the night sky and learn more about the mechanics of our universe. These communities often used their knowledge of astronomy for:Īncient astronomers from around the world made many early observations and predictions. Indigenous cultures around the world have long performed astronomical observation with the naked eye, frequently spotting stars, planets, and other celestial phenomena. In dark and remote places, before the advent of today's modern metropolises, the shimmering night sky must have looked truly alive. Countless generations have looked up at the night sky to observe its twinkling stars and dancing lights.
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