▲

An early champion of Chinese astrology, Gan De is credited with producing the first comprehensive star catalog in the world, sometime in the 4th century BCE, centuries before the Greek astronomy Hipparchus compiled his own atlas.

▲

More than a millennium before Nicolaus Copernicus introduced his heliocentric theory to the world, ancient Greek astronomer Aristarchus hypothesized, sometime during the 3rd of 4th century BCE, that it was the Sun, not Earth, that was the center of the universe.

▲

Humans have been turning their heads to the sky for as long as they have walked the Earth. It isn’t hard to imagine the sense of wonder the brilliant night sky must have instilled in our ancient ancestors.

▲

While Western advances in astronomy slowed to a near halt during the Dark Ages, astronomers in the Asian and Arab worlds continued to push the field further, creating and improving upon new measurement tools and constructing massive, beautiful observatories.

▲

In the 2nd century CE, Greek astronomer Ptolemy introduced the world to the ‘Almagest,’ which thoroughly described a massively influential, albeit inaccurate, geocentric theory of the universe. This idea that the Earth was the center of the universe would prevail for more than a thousand years, until the Italian Renaissance.

▲

One of the most well-known celestial events the world over, the passing of Halley’s Comet was first recorded in a Chinese text dating back to 240 BCE, and then again by the Babylonians in 164 BCE. Halley’s Comet passes Earth close enough to be visible to the naked eye every 75 years.

▲

The first written astronomical observations appear in Babylonian cuneiform texts written around the 1500s BCE. The earliest planetary observation was recorded in the ‘Enuma Anu Enlil,’ a section of which tracks the movement of Venus over the course of 21 years.

▲

The invention of the telescope was the most revolutionary development in the study of the stars in generations. Originally invented by Dutch lens maker Hans Lipperhey in 1608, the design was quickly improved upon and used extensively by Italian astronomer Galileo.

▲

A contemporary and opponent of Copernicus, Tycho Brahe, while rejecting the heliocentric theory, did make invaluable progress regarding the positions of stars using his massive observatory, Uraniborg. Built on the then-Danish island of Hven, Uraniborg was one of the largest and most important observatories in use before the invention of the telescope.

▲

In 1672, Italian astronomer Giovanni Cassini, with the help of his assistant Jean Richer, calculated the distance from Earth to Mars. This was the first proven distance from the Earth to another planet, and was instrumental in determining the true size of our solar system.

▲

English astronomer William Herschel discovered the first 'new' planet, Uranus, in 1781. Observations of Uranus had been made before, but up until the 18th century it had been incorrectly assumed that Uranus was a distant star, not a planet in our own solar system.

▲

In 1543, Copernicus published his heliocentric theory, sparking the Copernican revolution. It was the first time in more than a thousand years that a heliocentric theory had been posited, and while it was not immediately accepted, many astronomers after Copernicus subscribed to and improved on his theories until they became accepted as fact.

▲

It was at Uraniborg that Brahe worked on his star catalog, the final version of which consisted of over 1,000 stars. Finished at the end of the 16th century but not published until 1627, Brahe’s catalog included data up to 10 times more accurate than what was previously available.

▲

The stars were directly connected to the religions of prehistory. Ancient peoples quickly began to see celestial objects as beings responsible for earthly events such as rain, wind, and storms. Some of the world’s earliest structures and monuments were likely built as centers of worship in alignment with celestial events like the spring equinox.

▲

The ill-fated Carte du Ciel, an observatory project started in the last years of the 19th century, was a valiant attempt to photograph and catalog millions of stars from numerous locations around Earth, including the very farthest and dullest of stars. While more than 22,000 photographic glass plates were made, the project was eventually abandoned.

▲

One of Galileo’s greatest accomplishments, achieved with the help of his telescope in 1610, was the first observation of Jupiter’s four largest moons, known collectively as the Galilean moons. This was the first time satellites of another planet had been observed.

▲

The point of contention of the Great Debate of 1920 between American astronomers Harlow Shapley and Heber Curtis was how large the universe actually was. At the center of this argument was the Great Spiral Nebula. Shapley argued that this nebula was a small, relatively close by, cloud of gas and dust.

▲

Astronomers discovered the first black hole in 1964 in a deep part of the Cygnus constellation, after investigating unexpected x-rays in space. The black hole was named Cygnus-X, and proved for the first time Albert Einstein’s theory of black holes from nearly 50 years earlier.

▲

Curtis, on the other hand, successfully and correctly argued that the Great Spiral Nebula, now known as the Andromeda Galaxy, was, in fact, a massive and independent galaxy many light years away from our own Milky Way galaxy.

▲

The Soviet Mars 3 rover, launched in 1971, was the first probe to successfully land on Mars, although the transmission failed less than a minute afterwards. Five years later, in 1976, NASA successfully landed the Viking I and Viking II rovers on the red planet. These two rovers sent back over 52,000 images of the Martian surface over the course of four years.

▲

In 1980, American Nobel Prize-winning physicist Luis Alvarez, with the help of his son, geologist Walter Alvarez, and a team of nuclear chemists, was the first to posit that a massive asteroid colliding with the Earth was the extinction event that wiped out the dinosaurs and put an end to the Cretaceous period. Some years later, in the 1990s, the Chicxulub crater, measuring 110 miles (180 km) in diameter, was discovered in Mexico. Today, it is generally accepted that the Chicxulub crater was the impact site of that fabled asteroid.

▲

The 1920s saw one of the most shocking and revolutionary discoveries regarding the nature of space. The Hubble-Lemaître law, first hypothesized by Belgian priest and astronomer Georges Lemaître, later confirmed by Edwin Hubble, had proven that the universe itself is in a constant state of change and expansion. The Hubble-Lemaître law tells us that the speed at which a celestial object moves away from us is directly proportionate to its distance from Earth.

▲

One of the most important advancements in learning more about the history of the universe was the discovery of the universe’s cosmic microwave background, or CMG. In 1963, physicists Arno Penzias and Robert Wilson discovered the background radiation that is present throughout every corner of the universe and acts as a footprint for the cosmic events that came before. This discovery was instrumental in the widespread acceptance of the big bang theory.

▲

In 1992, a team of astronomers working out of the famous Arecibo Observatory found in the Virgo constellation two exoplanets, the first ever recorded, orbiting a dying star, called a pulsar. These were the first planets outside of our own solar system ever observed, but by no means the last. As of 2022, more than 4,000 exoplanets have been discovered.

▲

An international joint-research team led by NASA announced in 2019 that water vapor had been detected in the atmosphere of Europa, one of Jupiter’s 79 moons. This discovery supported the long-held theory that there is a massive ocean hiding underneath the surface of Europa, which many scientists believe to be a 15-mile (24-kilometer) deep sheet of ice.

Sources: (European Space Agency) (NASA) (Futurism)

▲

One of the most tantalizing questions of space exploration asks if there are any planets out there so similar to Earth that they could support life. In 2015, NASA announced they had found a very Earth-like planet, known as Kepler-452b, orbiting around a very Sun-like star. While the composition of the exoplanet’s atmosphere is unknown, what is known is that it is a habitable distance away from its home star, and has a rocky surface.

▲

What propelled this expansion, however, was still unknown in the times of Lemaître and Hubble. It wasn’t until 1998 that scientists discovered dark energy. There is more dark energy in the universe than there is anything else; 69% of the universe is dark energy. Unlike matter and dark matter, dark energy seems to be spread out evenly across the universe, and is gravitationally repulsive, meaning its energy pushes outward, thus pushing everything in the universe further apart. To this day, dark energy remains one of the universe’s greatest mysteries.

▲

Edmond Halley, an English scientist and astronomer, while comparing contemporary charts and star positions to those that Ptolemy recorded in ‘Almagest,’ was the first to realize that the distant stars in the sky were moving and dynamic, not fixed, static objects as was previously believed. It was after him that Halley's Comet was named.

▲

Long thought to be an incredibly dry planet, devoid of water, humanity’s perception of Mars changed in 2012 when NASA’s Curiosity rover found evidence of a massive waterbed frozen under Mars’ surface. Since then, numerous other discoveries of water have occurred, and scientists now agree that at least one third of Mars is covered in frozen water.

▲

SMACS 0723 is a huge cluster of galaxies that is billions of years old. The image is streaked with red arcs, which NASA explains are caused by the powerful gravitational field of SMACS 0723 bending light from distant galaxies behind it. Now that we've seen some of the most amazing developments in modern astronomy, let's look back to the very beginning.

▲

The James Wedd captured this incredible, never-before-seen detail of Stephan's Quintet—a group of galaxies located in the Pegasus constellation, approximately 290 million years away.

▲

The monumental telescope (which cost US$10 billion) took decades to develop and is the size of a tennis court. On July 12, 2022, it was deemed ready for scientific exploration, and the first images were shared with the world. The telescope has been tuned to see the sky in infrared which means we'll be able to see more than ever before. In fact, it can observe cosmic events that occurred much further back in time, 13.5 billion years to be exact! So far, it has captured never-before-seen nebulae and clusters of galaxies that are millions of light-years away.

▲

For as long as humans have walked the Earth, the great endless sky and the countless stars that fill it have left us in a state of awe-inspired wonderment. Similarly, the study and exploration of space have been a priority for humankind for millennia. From the ancient Assyrians and Greeks, to the greatest minds of the Renaissance, and up to the billionaire space explorers of the 21st century, incredible amounts of time and effort have gone into better understanding our celestial surroundings. And yet, despite all of the great strides that have been made to understand the great beyond, it's estimated that 95% of the universe is still undiscovered.

Click through the gallery to learn about some of the greatest discoveries of astronomy and our universe.