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Astronomy is often considered the oldest of sciences. Ancient cultures around the globe marveled at the sky and its stars, yet it wasn't until the 17th-century scientific revolution that astronomers started to understand the true nature of the cosmos. These groundbreaking revelations laid the foundation for the captivating view of the universe we hold today. Below are a few pivotal moments that shaped our cosmic knowledge.
10. The First Theory Suggesting Stars Are Similar to the Sun
Humans have charted the stars for millennia, but for much of history, their true nature remained a mystery. The realization that stars are essentially distant suns didn’t emerge until the 16th century. In 1584, the Italian philosopher Giordano Bruno proposed several groundbreaking ideas, many of which we now accept as fact. He suggested that stars were like our Sun, only far away, and might even host planets similar to Earth. Bruno also speculated that the universe could be infinitely vast.
Naturally, being a visionary in the field of astronomy wasn't exactly a benefit in the 16th century. In 1592, the Catholic Church imprisoned Bruno, and he was ultimately burnt at the stake eight years later. However, over the course of the next century, his revolutionary ideas gained widespread acceptance among the scientific community.
9. The First to Measure Stellar Distances and Coin the Term 'Light-Year'
Once it was accepted that stars were distant suns, scientists began to ask the natural question: just how far away are they? The first to measure this distance was the Russian astronomer Friedrich Bessel. He focused on the star 61 Cygnus, and his measurement was akin to standing in San Francisco, gazing at a pizzeria in New York (the best pizzas, naturally), and calculating the distance. In 1838, he used the parallax technique to estimate the star's distance at 10.3 light-years—close to the modern value of 11.4. This was an extraordinary feat at the time. Bessel made huge contributions to astronomy, having mapped the positions of an incredible 50,000 stars.
8. The Invention of the First Telescope
The first patent for the telescope was filed by a Dutch eyeglasses maker named Hans Lippershey. In 1608, he developed a device that offered 3x magnification. However, like all great inventions, the telescope’s creation was not without controversy. It was also the story of the invention of the microscope, as both instruments were essentially the same at the time. Lippershey’s hometown of Middelburg was also home to Hans and Zacharias Janssen, a father-and-son lens-making duo who claimed the invention for themselves and accused Lippershey of stealing their idea. Another Dutch optician, Jacob Metius of Alkmaar, filed a similar patent a few weeks after Lippershey’s.
The Dutch lens-makers were so preoccupied with arguing over who invented the magnification device that none of them used it for astronomy. That distinction goes to Galileo, whose groundbreaking work we've discussed before. Galileo’s telescope eventually reached 10 times the magnification of the original devices, although, notably, none of the Dutch opticians faced charges of heresy.
7. The First Discovery of an Asteroid
There are over a million asteroids within our solar system (which is quite a lot). However, most of them are very small. The largest, Ceres, is a dwarf planet situated in the asteroid belt, and even it is only a fraction of the size of the Moon. Because of their tiny size, astronomers didn't spot any asteroids until 1801. Swiss scientist Giuseppe Piazzi was observing stars when he noticed a relatively dim object that kept moving. After weeks of watching it, he thought he had discovered a tail-less comet, but it was later classified as a planet. In truth, it was neither; it was Ceres.
In some respects, early astronomers found asteroids to be more of an inconvenience than a discovery. They were nicknamed the 'vermin of the skies' for their tendency to leave streaks on photographs of stars. Nearly 100 years after Piazzi's discovery, the first asteroids near Earth were found, which paved the way for cultural milestones like Deep Impact and Armageddon.
6. The First Use of Spectroscopy
'Of all objects, the planets are those which appear to us under the least varied aspect. We see how we may determine their forms, their distances, their bulk, and their motions, but we can never know anything of their chemical or mineralogical structure.' This observation was made by French philosopher Auguste Comte in 1842. While his view was dramatically incorrect, it was understandable at the time, as the only way to determine the composition of objects was by bringing them into a laboratory — which was, of course, impossible for stars and planets.
The method that disproved Comte's belief is called spectroscopy. It involves passing light through a grating onto a surface, creating a pattern of lines. Each element emits light at a specific wavelength, and each wavelength generates a unique line pattern. By applying this technique to starlight (or any other light), astronomers can determine the composition of celestial bodies, even across unimaginable distances. The man credited with inventing this technique in the early 19th century was Joseph von Fraunhofer, who used it to study light from the Sun and Moon. Fraunhofer also developed the heliometers used by Bessel to measure distances.
5. The First Photograph of an Object in Space
While the naked eye could gather some valuable information about the solar system, it had its limits, and the invention of photography in the 19th century revolutionized astronomy. The first person to direct a camera towards the sky was Louis Daguerre in 1839, capturing an image of the Moon as he slowly followed its movement across the sky. Unfortunately, his lab burned down shortly after, and his work was lost. The oldest surviving photograph of the Moon dates back to 1851, taken by John Adams Whipple. Despite this, Daguerre’s contribution is still honored, as the photographic process he used is known as a daguerreotype.
4. The First Observation Outside the Visible Spectrum
Both photography and naked-eye observation share one limitation—they are both confined to the visible spectrum of light. Today, astronomers examine the sky using everything from radio waves on one end of the electromagnetic spectrum to gamma rays on the other, unlocking a wealth of information about the universe. The discovery of infrared radiation, which has a wavelength just longer than visible light, was made by British physicist William Herschel in 1800. This marked the first time we detected non-visible radiation from space.
It took over fifty years for Charles Piazzi Smyth to measure infrared radiation from the Moon, which he accomplished in 1856. A more significant contribution came in 1870 from the fourth Earl of Rosse, who used infrared measurements to estimate the Moon's surface temperature to be a balmy 500 °F (though we now know it’s closer to 250 °F during the day). As the British magazine The Spectator wrote at the time, 'It seems strange to learn from science that the full moon is so intensely hot that no creature known to us could long endure contact with her heated surface. Such is the latest news which science has brought us respecting our satellite.'
3. The First Galaxy to Be Observed
Beyond our own Milky Way, the earliest record of another galaxy being observed dates back to 964 AD. Persian astronomer Abd-al-Rahman Al Sufi documented our closest neighbor, Andromeda, referring to it as a 'little cloud.' He had no concept of what it truly was, as it was nearly a millennium before Edwin Hubble confirmed the existence of galaxies as we understand them today.
In 1924, Hubble turned his telescope toward Andromeda and, by measuring the brightness of stars, determined that it was 860,000 light-years away, far beyond the confines of the Milky Way. Until that discovery, some believed that the Milky Way was the entire universe.
2. The First Measurement of the Speed of Light
When Bessell measured the distance to 61 Cygnus in light-years, he was able to do so because he knew the speed of light. This had first been measured nearly two centuries earlier, in 1676, by Danish astronomer Ole Roemer. Prior to this, the concept of light having a speed was debated, with many natural philosophers believing light traveled instantaneously or so quickly that it made no difference. Roemer didn’t aim to settle this debate; his discovery was actually accidental.
Roemer had been observing the eclipses of Jupiter’s moons for navigational purposes. Over many years, he noticed that the eclipses occurred later than expected when Earth was farthest from Jupiter and earlier when Earth was closer. Roemer hypothesized that this delay in timing was due to the longer time it took for light to travel when the distance was greater. Dutch scientist Christiaan Huygens later performed calculations on Roemer’s data and determined that the speed of light was around 210,824 kilometers (131,000 miles) per second, a figure close to the modern value of 299,792 kilometers (186,000 miles) per second.
1. The First Prediction of a Solar Eclipse
One of the first things early astronomers noticed was that the movements of celestial bodies followed a predictable pattern. If they had the concept of clockwork, they might have used it as a fitting analogy. The ability to forecast the positions of planets came long before humans understood what those planets actually were. Among the most impressive events we can predict are solar eclipses, with NASA listing them as far into the future as the year 3000.
The earliest known prediction of a solar eclipse was made by Thales of Miletus in 585 B.C. According to Greek historian Herodotus, Thales predicted an eclipse during a battle between two empires in what is now Turkey. The eclipse caused the soldiers to pause and lay down their weapons, leading to a peace treaty that ended 15 years of conflict. Sadly, astronomical events no longer have the power to resolve international wars.
