A brief history of astronomy
Credit: NASA/Bill Dunford
Countless generations have looked up at the night sky to observe its twinkling stars and dancing lights. In dark and remote places, before the advent of today's modern metropolises, the shimmering night sky must have looked truly alive.
Early days (and nights)
Indigenous cultures around the world have long performed astronomical observation with the naked eye, frequently spotting stars, planets, and other celestial phenomena.
These communities often used their knowledge of astronomy for:
- Navigation
- Timekeeping
- Agricultural planning
- Spiritual and religious practices
A closer look at the heavens
Ancient astronomers from around the world made many early observations and predictions. Historical records include many star charts, which reveal clear efforts to map the night sky and learn more about the mechanics of our universe.
Some examples of early discoveries include:
- Planets versus stars
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Babylonian 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. They concluded that something fundamentally different existed: these five points of light were not stars at all. 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.
- A spherical Earth
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As early as the 6th century BCE, ancient Greek philosophers documented evidence that Earth was a sphere. They noted that the night sky looked different when seen from various locations on Earth, hinting at our planet's curved surface. They also observed the round shadow of Earth on the Moon during lunar eclipses. These philosophers were even able to calculate the circumference of Earth quite accurately. They did this by measuring the length of the shadow cast by an object at exactly the same time, in two different locations. 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. That is very close to the real value of 40,075 kilometres!
- Bright supernovae
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In the year 185, Chinese astronomers became the first to document a supernova. Several supernova explosions have been observed since then, including a particularly bright one in the year , which (at its peak) was four times brighter than planet Venus, one of the brightest objects in the night sky. Some supernovae are even bright enough to be visible during the day!
- Cloudy galaxies
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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. Before then, nearby galaxies were thought to be cloudy regions of the Milky Way. 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."
The astrolabe, such as this one developed in 1553 by French clockmaker Jean Naze, is a navigational tool that can determine local time and location in latitude based on the position of celestial objects. Although the Sun is most commonly used, a total of 58 recognized "navigational stars" can help calculate the user's location. One method of astronavigation even uses the angle of the Moon to calculate time, a key piece of information for pre-modern sailors travelling on unfamiliar seas. (Credit: Marie-Lan Nguyen)
The Copernican revolution
Before the 16th century, Earth was commonly thought to be at the centre of the solar system, with all other celestial objects revolving around it. This is known as the geocentric model. This theory, however, did not match some confusing observations made by astronomers, such as the path of planets that appeared to move backwards on their orbits.
When we observe, from Earth, the planets around the Sun, they do not always appear to be moving in one direction in our sky. Sometimes they appear to loop backwards for short periods of time. 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.
In 1543, Polish astronomer Nicolaus Copernicus proposed a heliocentric model of the solar system in which the planets orbit the Sun. This model explained the unusual path of planets that astronomers had observed. The new theory was one of many revolutionary ideas about astronomy that emerged during the Renaissance period.
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. This progress dramatically improved humanity's understanding of the universe. Their observations and investigations were strengthened by the invention of the telescope in the early 17th century. Italian astronomer Galileo Galilei popularized the use of telescopes to study and discover celestial objects, including Jupiter's four biggest moons. In his honour, they are known as the Galilean moons.
An expanding universe of knowledge
Over the following centuries, astronomers around the world formalized the study of the sky by creating detailed catalogues of stars, star clusters, and nebulae. After discovering Uranus in , William Herschel opened new areas of research in by discovering infrared radiation – a type of light that is not visible to the human eye.
Others took advantage of rapid progress in the fields of optics and imaging. In , Edwin Hubble fundamentally changed the scientific view of the universe when he used the 2.5 m-diameter Hooker Telescope to prove that the Andromeda Nebula extends beyond our Milky Way Galaxy.
Hubble's discovery of the universe's ongoing expansion also paved the way for other astronomers to theorize its origin. The Big Bang theory, first proposed by Georges Lemaître, was later bolstered by strong evidence: the discovery of the cosmic microwave background (CMB), faint "noise" left over from the massive explosion that gave rise to everything in the universe. The CMB was accidentally discovered by radio astronomers just five years before the Apollo 11 Moon landing.
Improvements in satellite launch and design allowed astronomers to collect even more data about planets within our solar system in the second half of the 20th century. Several robotic space probe campaigns, including Mariner, Venera, and Voyager, ventured farther than ever before.
Astronomy today
The James Webb Space Telescope, a collaboration between NASA, the Canadian Space Agency and the European Space Agency, is the most complex and powerful space telescope ever built. It is helping scientists better understand the universe from its location in space. (Credit: NASA)
Today, astronomers collect data about celestial objects by using huge telescopes on the ground as well as in space. These modern telescopes equipped with massive mirrors allow astronomers to capture the light of very faint and faraway objects. Specialized techniques and sensitive scientific instruments have been developed to study not only visible light, but also the entire electromagnetic spectrum of light including infrared light, radio waves and X-rays.
Large, complex telescopes and advanced techniques have even enabled astronomers to directly observe phenomena including black holes, distant exoplanets, and gravitational waves.
Thanks to the sheer size of its 6.5-metre-diametre golden mirror, the James Webb Space Telescope is the largest space telescope ever built. Launched in , Webb uses its precision instruments to peer into clouds of cosmic dust to collect infrared light from distant stars and galaxies, giving Canadian astronomers a groundbreaking glimpse of the earliest moments of our universe and never-before-seen planets circling other stars.