Astronomy, as we usually think of it, involves the use of a telescope in order to better see distant objects in the sky -- whether it's the small-scale amateur version, a bigger telescope housed at an observatory or one stationed in space, like the Hubble. Although Galileo Galilei is sometimes credited as the inventor of this amazing tool, we can actually credit three lens and instrument makers in the Netherlands with the first patent applications for the refracting type. Soon after, Galileo improved upon these concepts. Then in 1668 -- 60 years later -- Isaac Newton built the first actual refracting telescope.
Of course telescopes have made locating celestial objects much easier, but people were making important astronomical discoveries long before its invention. For example, astronomers were employing the astrolabe -- essentially a type of manual calculator used to help locate the stars, sun, moon and planets -- since at least 150 B.C. And even after telescopes became ubiquitous, astronomers continued using other means to discover and predict astronomical phenomena. In this list, we'll run down some astronomical discoveries that had nothing to do with the telescope.
If you've ever witnessed an eclipse, you understand what a wondrous sight it can be. Now imagine how they appeared to people thousands of years ago, before it was understood exactly what was happening when the moon passes in front of the sun. No wonder eclipses have long been given religious significance.
However, exactly when the first solar eclipse occurred is a matter of dispute -- aligning sometimes vague historical records with the exact date of an eclipse based on what we know of their cycle can be difficult. One Chinese story recounts the tale of Ho and Hsi, astronomers who got drunk and failed to predict an eclipse around 2134 B.C. Other Chinese astrological texts mention eclipses as far back as 2800 B.C. An Irish archaeologist and astronomer named Paul Jordan believes he has found evidence in Neolithic stone carvings of an eclipse occurring even earlier -- 3340 B.C. -- although this hasn't yet been substantiated.
Through repeated observation, ancient astronomers learned how to predict eclipses and drew conclusions about the relationship between the sun, Earth and moon. Historical records of solar eclipses are invaluable. Since we can now predict when they will occur down to the second, historians can use records of past eclipses to date other events. Astronomers can also use them to learn how the Earth has changed over time.
Solar eclipses may have been recorded as far back as 3340 B.C.
Image Credit: Photodisc/Thinkstock
9. Auroras
Those of us living in the northern latitudes tend to only think of the aurora borealis, the beautiful red or green curtain-like glow of energized particles in the Earth's magnetosphere that occurs around the North Pole. However, there's also the equivalent in the southern latitudes, known as the aurora australis. Auroras are rarely seen outside of polar regions. This makes their presence in historical records even more significant, because sighting them elsewhere tells astronomers much about what was happening in the Earth's atmosphere at the time.
There is evidence that Cro-Magnon man witnessed auroras; cave paintings dated to 30,000 B.C. depict macaroni-like swirls in a sky. The first written description probably occurred in 2600 B.C. in the "Bamboo Album of Chronology" by Chu-Shu-Chi-Nien. He wrote, "Fu-Pao, the mother of the Yellow Empire Shuan-Yuan, saw strong lightning moving around the star Su, which belongs to the constellation of Bei-Dou, and the light illuminated the whole area" [source: NASA]. Bei-Dou is the Chinese term for the constellation also known as Ursa Major.
A large geomagnetic storm in 1859 resulted in two auroral events that could be seen in the United States, Europe, Australia and Japan. The atmospheric electricity affected telegraph lines, allowing telegraph operators to use "auroral current" rather than battery power for communication. This marked the first time that astronomers linked electricity with auroras.
The aurora borealis can be seen at certain times of the year in the North Polar region.
Image Credit: Digital Vision/Thinkstock
8. Constellations
Today, the International Astronomical Union (IAU) uses the term "constellation" to mean a specific region on a grid in the celestial sphere -- an imaginary circle surrounding the Earth upon which the stars are "fixed." Traditionally, a constellation is a pattern formed by stars in the sky (which the IAU calls asterisms). These patterns rely both on the visible relationship between the stars (they appear "close" to us although they may actually be many light years apart) and human imagination. Because of this, different cultures around the world have their own systems of constellations.
In the Western world, we tend to think of the constellations as originating with the ancient Greeks. However, the original 40 constellations described by Ptolemy in A.D. 150 were based on star lists on Babylonian cuneiform dating back to 687 B.C. In turn, this system was likely based on even earlier Sumerian concepts. Another 44 constellations were added over the years to create the system recognized by the IAU today. It appears that Chinese astronomers were the earliest recorders of a constellation system -- star maps made of stones have been found in tombs dated to 4000 B.C. They weren't that familiar with the sky around the South Pole, but the Chinese astronomers would add more asterisms to their maps after learning the Western system of constellations.
7. Heliocentrism
Heliocentrism is the idea that the Earth and other planets revolve around the sun. Thousands of years ago, it was a common belief that the sun revolved around the Earth instead -- and giving voice to a differing theory could be dangerous. Galileo was forced to recant his assertion of the heliocentric model in the early 1600s because the Roman Catholic Church found them contrary to the Bible.
Galileo had based his beliefs on those of Copernicus, the first person to come up with a mathematically based heliocentric model in his 1543 book, "On the Revolutions of the Heavenly Spheres." But the idea didn't start with Copernicus, either -- he was resurrecting the arguments of Greek astronomer Aristarchus, the first to state that the sun was the center of the known universe in about 270 B.C. (the distinctions of solar system and galaxy didn't come until the 19th century).
He also correctly put the planets in order of their distance from the sun, based on observations and geometric calculations. Aristarchus' contemporaries didn't buy into his theory, but it took hundreds of years after Galileo for acceptance of heliocentrism to become widespread. According to a 1999 Gallup poll, about 18 percent of Americans still aren't sure [source: Gallup].
6. Comets
Although there are nearly 4,000 known comets in our solar system, we need telescopes or, at the very least, binoculars to see most of them. Comets spotted by the naked eye tend to be faint and typically are only spotted once a year or so. These tailed balls of ice, dust and gas confounded ancient people with their mysterious comings and goings. Comets were often thought to be bad omens -- foretelling the deaths of kings, wars or even just a bad harvest.
The oldest known record of comets was found in a Chinese tomb in the early 1970s. Dated to 168 B.C., the tomb at Mawangdui included texts written on silk. Among the more than 100,000 words on everything from cartography to music are astronomical descriptions, including identifications of different types of comets and what type of event each one would foretell. One of the most famous, Halley's Comet, was probably first sighted and recorded by the Greeks in 466 B.C. Why aren't we sure, though? Before the invention of the telescope, ancient astronomers and observers were typically not aware that they were spotting the same comet they'd seen before. Now that we can predict the orbit of Halley's Comet (and other short-period comets), astronomers can use computer models to retrodict the comet's orbit and match it to reported sightings.
Halley's Comet as it crosses the Milky Way, from the Kuiper Airborne Observatory in 1986.
Image Credit: NASA
5. Sunspots
Sunspots are dark areas where temporary disruptions in the sun's inner magnetic field have blocked the flow of light, heat and energy to the surface. The sun has a life cycle of its own (lasting roughly 11 years) and sunspots play a huge role. They're also related to a host of other phenomena like solar flares, solar wind and coronal mass ejections, all of which can have an influence on Earth.
Once again, Chinese astronomers appear to take the prize for first noticing and recording this phenomenon. In 364 B.C., Gan De created a star catalogue -- a description of all of the known stars at the time -- which also contained references to the placement of sunspots. Official imperial histories of China dating to 28 B.C. contain sunspot records, including the tracking of their movements over time. These Chinese records are not only the oldest, but also the longest continuous record of sunspots, as they were kept until 1630. Sunspots were not mentioned in Western literature in A.D. 807. However, prior to Galileo, most of these observers believed they were seeing transits of planets in front of the sun. Sunspots gave credence to the theory of heliocentrism, because their movements and temporary nature showed that the sun rotated and changed.
Image Credit: NASA /TRACE
4. Planetary Movement
If you locate and observe the other planets in the night sky above Earth, it will initially appear that they are stationary. Slower-moving planets like Uranus have an orbit of almost 84 years, so it would take quite awhile to notice any real change there. But Venus' year is shorter than ours at 255 days, so over time you would notice that it appears to be moving across the sky. Some planets lap Earth, while others move so slowly that they appear to stop, then move backwards (called retrograde).
Although it took thousands of years for astronomers to accept the theory of heliocentrism, ancient stargazers did become aware that the planets were rotating as well as orbiting around a central location. However, they weren't always aware that they were seeing the same planet. Ancient Greeks, for example, called the planet Mercury "Apollo" when they saw it in the morning sky and "Hermes" when they saw it in the evening.
The Greek astronomer Hipparchus accurately created geometric models of both lunar and solar motion in about 150 B.C. He measured angles using instruments that preceded the astrolabe and used trigonometry to make calculations. About 150 years later, Ptolemy, a Roman citizen living in Egypt, expanded upon the work of Hipparchus and others to create models of planetary movement. He also understood the retrograde motion -- and that planetary orbits varied.
3. Neptune
Not all of the planets are visible from Earth with just the naked eye and, even when spotted, they were sometimes mistaken for other planets. The term "classical planets" has been used to describe all of the celestial bodies in the sky that weren't fixed and were visible to the ancients. These include Mercury, Venus, Mars, Saturn and Jupiter, as well as the moon and the sun. Technically, Uranus is visible on very clear nights, but it's so dim that it doesn't stand out enough amongst the stars to be recognized as a planet.
The invention of the telescope allowed for the discovery of numerous planetary moons and other celestial objects, but one of the planets was discovered without it. Neptune was the very first planet to be discovered not through observation of any kind, but through the use of math. Astronomers had been able to accurately predict the orbits of other planets like Jupiter and Saturn, but the orbit of Uranus had unexplained variations. Three days after astronomer Alexis Bouvard's death in August 1846, another French cosmologist named Urbain Le Verrier announced that he had discovered the cause of Uranus's perturbation: the gravitational pull of a previously unknown planet nearby. Le Verrier had spent nearly six months performing complex calculations before coming to this conclusion. Neptune's existence was confirmed by telescope in September 1846.
Neptune as seen from space. This planet wasn't discovered through direct observation, but through mathematical calculations.
Image Credit: Jason Reed/Photodisc/Thinkstock
2. Speed of Light
The speed of light may not be an actual "thing" like most of the other astronomical discoveries on our list, but it's no less important. The speed of light is a constant (c), and used in many areas of study, including physics, astronomy and computing. It is part of Einstein's famous mass-energy equivalence (E=mc2). No matter what type of light or other forms of electromagnetic radiation, in empty space light will always travel at 299,792,458 meters per second (186,282 miles per hour).
Galileo tried unsuccessfully to measure the speed of light several times. Danish astronomer Ole Rømer succeeded in 1676 after observing the lunar eclipses of Jupiter, especially those of its moon, Io. When the Earth was closer to Jupiter, the times between the eclipses were shorter than when the two planets were farther apart. Rømer believed that this must mean that the speed of light was finite, as it was taking longer to reach Earth when Jupiter was farther away. His measurements were very close to the actual speed of light as we know it today. Over the centuries, increasingly precise measurements were obtained. In 1975, an instrument called a laser inferometer was used to obtain the current measurement, and subsequently the definition of a meter was changed to "the length of the path traveled by light in vacuum during a time interval" of one-299,792,458th of a second [source: BIPM].
1. Radio Astronomy
We'll end our list of astronomical discoveries made without a telescope with something completely different -- radio waves in outer space. Although we mainly think of the ones that we generate and transmit for communication -- radar, GPS, computers and more -- radio waves also occur naturally. Essentially, the term just means a specific type of wave on the electromagnetic spectrum (which includes X-rays, light, ultraviolet and several other types).
In 1865, Scottish mathematician and physicist James Clerk Maxwell predicted radio waves, and their existence was proven when German physicist Heinrich Hertz generated them in a laboratory in 1887. The field of radio astronomy was born 44 years later when American physicist and radio engineer Karl Jansky discovered that there were radio waves coming from the Milky Way. Jansky worked for Bell Laboratories and was seeking possible sources of static interference with voice transmissions. After long observation and studying astronomical maps, he discovered that one source was cosmic radio waves.
Jansky published a paper on the subject and wanted to explore it further, but Bell Labs wasn't interested. Some speculate that Jansky would have won a Nobel Prize for his research had he not died at the young age of 44 due to a heart condition. Today, the unit of measurement for the strength of radio sources in the field of radio astronomy is called a Jansky in his honor.
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