In the day to day hustle and bustle of life, it often feels as though there's little time to think far beyond the walls of your school, office or home, much less the outer reaches of the universe. But since the beginning of civilization, mankind has struggled to explain the mysterious workings of celestial bodies.
Around 2000 B.C. the Egyptians constructed the first solar-lunar calendars and around 130 B.C. the Greek Hipparchus developed the first accurate star map [source: Russell]. Since then, we've walked on the moon, launched probes and robotic rovers into space and glimpsed the birth of stars.
Yet the quest to learn more continues. Cosmology, a branch of astronomy that attempts to explain the origin, evolution and fate of the universe, is alive and well, thanks to the impressive achievements of people like Newton, Einstein and Hubble. In this collection of the top cosmological achievements, you'll learn about 10 of the highlights. Without the first achievement, it's unlikely such a list would even exist.
10. The Invention of the Telescope
In 1608, the Dutchman Hans Lippershey put two glass lenses in a narrow tube and changed the course of history. Initially, though, the first telescopes were sold across Europe as little more than curios. It wasn't until Galileo turned the nifty device toward the stars in 1609 that things really got interesting.
The powerful light-gathering ability of the telescope enabled Galileo and others to view objects in space never before seen. With it, Galileo discovered that Jupiter had moons, Venus experienced phases and that our moon was mountainous. These discoveries were significant for a number of reasons. For one, the fact that moons orbited Jupiter showed that Earth was not the only center of motion, as previously believed; meanwhile, the fact that the moon had a similar landscape to ours contradicted the previous notion that objects in space besides Earth were made of a perfect heavenly substance.
Current telescopes, which use mirrors instead of lenses, are even larger and more powerful than the ones used by early astronomers, enabling scientists to look back almost to the beginnings of the universe. The telescope is largely responsible for much of what we know about the universe today. In fact, several of Galileo's telescopic observations helped confirm the validity of heliocentrism, the next achievement on our list.
9. Sun-centered Universe
In A.D. 140, the Greek astronomer Ptolemy put forth the theory of geocentrism, the idea that all objects in the universe revolve around the Earth. While the theory required a series of complicated adjustments to accurately describe the motions of the planets, it meshed well with the popular religious beliefs of the day and so went unquestioned for nearly 1,500 years.
It wasn't until 1543 that Nicolaus Copernicus introduced an alternate theory, suggesting that it wasn't the Earth that was the center of the universe but the sun.
While this heliocentric theory flew in the face of church beliefs, which held that God's concern for humankind dictated Earth be at the center of everything, it was able to predict the motion and positions of the planets with much more accuracy. Although it took some getting used to -- the thought of the Earth moving without anyone knowing seemed the height of absurdity at the time -- many regard the eventual acceptance of Copernicus's model as the beginning of the modern era of astronomy and cosmology [source: HowStuffWorks, History].
Yet things were far from perfect. It wasn't until Sir Isaac Newton came along and introduced a few laws of motion that things really got moving.
8. Newton's Laws of Motion
Sir Isaac Newton is widely considered one of the greatest scientists in history. Not only did he achieve several breakthroughs in the field of optics and significantly improve upon the telescope with the introduction of mirrors, but he's also to thank for that Calculus course you barely passed in high school. Newton's greatest achievement, though, was his publication in 1687 of the "Principia," in which he introduced the Three Laws of Motion -- inertia, acceleration, and action and reaction.
With the realization that these laws applied not only to everything on our own planet but to every object in the universe, the face of astronomy was forever altered. The equations Newton developed in relation to each of the Laws have enabled a number of monumental cosmological discoveries. In 1758, for instance, Edmund Halley used Newton's laws to accurately predict the exact date and location of a comet's reappearance. We now know that comet as the famous Halley's comet. The Laws have also been used to determine the masses of the planets and to discover the existence of Neptune [source: Anderson].
Despite their wide range of applications, though, something was still lacking. Newton's greatest triumph is next.
Before Newton described the Law of Universal Gravitation, we were all just floating around in space. Well, not exactly, but our understanding of the universe was. While not entirely perfect, as we'll find out in the next section, the Law of Universal Gravitation (along with Newton's previous three Laws) laid the foundation for our current understanding of how objects in space behave. Gravity is not only keeping you firmly in your chair as you read this, but among other things, it's also holding together the Sun and planets and holding together stars in other galaxies.
Introduced along with Newton's Laws of Motion, the Law of Gravitation explained that all objects had a force of attraction between them and that this force was directly proportional to their mass. This realization helped to explain why the moon orbits around the Earth instead of the other way around. Gravity also explains why the planets orbit the Sun the way they do, how cosmic bodies form and how stars die. Additionally, when he combined it with his Laws of Motion, Newton was able to use his ideas about gravity to mathematically confirm all of Kepler's laws, bringing them out of the realm of mere supposition.
But there were still a few wrinkles to iron out. For one thing, Newton's laws couldn't quite account for discrepancies observed in Mercury's orbit, which was not as predictable as it should have been. Neither could they explain whygravity existed. It took another three centuries for that to happen.
6. General Relativity
While Newton's theory of gravity worked perfectly well in most situations, there was still the question of why it was there. Enter Albert Einstein and his new theory of gravity. Introduced in 1915 and known as the General Theory of Relativity, the new theory stated that gravity is caused not by a gravitational field as Newton suggested, but by a distortion of space and time. According to Einstein, bodies of mass actually warp the fabric of space, creating a curve. It is this curve that causes planets to move the way they do (effectively "falling" into orbit around far more massive objects such as our sun) rather than an actual physical force of attraction.
Not only does general relativity account for the previously unexplained peculiarities in Mercury's orbit, but it also explains the bending of light by the sun. Furthermore, the theory yields formulas that can be used to describe cosmic scenarios such as the collision of black holes. Despite the great strides of Newton and Einstein, though, there's still much to be learned about gravity and exactly how it behaves. Nevertheless it comes as no surprise that Einstein's Theory of General Relativity is considered one of the foundation blocks of modern physics [source: Dine].
The next achievement takes us to Southern California to peer out of one of the world's largest telescopes.
5. The Milky Way is not Alone
Up to this point in our story, cosmology's achievements have dealt only with our own solar system. It wasn't because scientists like Galileo and Newton were self-centered, though. They simply couldn't be sure that other groupings of stars existed beyond our own. It took a man by the name of Edwin Hubble, some complex measurements and equations and a giant 100-inch (254-centimeter) telescope to figure that out.
In 1919, Hubble was able to use the Hooker telescope on Mount Wilson in Southern California (the largest telescope at the time) to observe a unique type of star called a cepheid variable in a series of nebulae. At the time, astronomers disagreed about what exactly nebulae were -- some perceived them to be little more than clouds of gas within our own galaxy, while others suspected they may be entirely separate galaxies beyond our own. Using what was known about the relationship of a star's brightness and its distance from Earth, Hubble was able to calculate how far away the variable stars were. His discovery -- that the stars were at least eight times farther away than the most distant stars in the Milky Way -- proved conclusively that the nebulae were indeed separate galaxies and Hubble himself went on to discover at least 23 more [source: PBS]. Since then, thanks to the telescope named in Hubble's honor, we've learned that the universe in fact contains nearly 100 billion such galaxies [source: Space Telescope Science Institute].
But Hubble wasn't done yet. His next discovery was so startling that Einstein was afraid to even acknowledge it.
4. Universe Expansion
Soon after Hubble shocked the world of astronomy by declaring our galaxy was not alone, he made another startling discovery. Not only was the Milky Way galaxy one among many, but it was also hurtling through space at a constant speed.
Hubble was able to make this discovery by building on the work of Christian Doppler, who in the 1840s discovered that an object's motion could be determined by analyzing its light. Basically, when objects are moving away from us, their wavelength of color shifts toward the red end of the color spectrum and when they're moving toward us, it shifts to the blue end. The degree of the color change indicates the object's speed. Using this knowledge, known as the Doppler color shift, Hubble and a colleague measured and analyzed the movement of countless galaxies.
What they found was startling: Every galaxy outside of our own local group showed a red shift, indicating that they are all moving away from us. The movement of the galaxies also followed a distinct pattern that increased with their distance from us. This pattern of motion is now known as Hubble's Law and led to the conclusion that the universe was indeed expanding. Naturally, this was a difficult concept to grasp: As you learned earlier, Einstein was so disturbed by it that a decade earlier he bungled some of his own equations to prevent it.
But bungled equations don't make something stop happening. So the next logical step was to ask the question "why?" And that leads us to the next achievement on our list.
3. Big Bang Theory
Two years before Hubble proved definitively that the universe was expanding, another scientist by the name of Georges Lemaitre had actually come to the same conclusion. Although he lacked concrete evidence, he concluded universe expansion was the logical deduction based on Einstein's theory of gravity. In 1927, he also suggested that if indeed the universe was expanding as he expected, it must have at one time been condensed into a smaller point -- a primordial atom that contained all the matter in the universe [source: PBS]. This idea formed the basis of what we now hold as the Big Bang Theory, the most widely accepted theory for the origin and development of our universe.
In its simplest terms, the Big Bang Model says that between 12 and 14 billion years ago, all of the space, time, matter and energy of our universe was condensed into a hot state a few millimeters across and then expanded into the universe we know today. Along with the discovery that the universe is expanding at a constant rate, the Big Bang Theory has received support from a number of other observations as well. To learn more about such observations, we turn to the next item on the list, cosmic background radiation.
2. Cosmic Microwave Background Radiation
This next achievement happened much by accident. Arno Penzias and Robert Wilson were building a radio receiver in 1965 when they picked up a source of excess noise. This "noise," which had actually been predicted earlier but never confirmed, turned out to be nothing less than the remnant heat left over from the big bang. Penzias and Wilson went on to receive the 1978 Nobel Prize in Physics for their discovery.
Today, this leftover heat, or cosmic microwave background radiation (CMB), is actually very cold -- just 2.725 degrees above absolute zero -- and is measured in microwaves. It is also highly uniform across the entire sky -- to better than one part in one thousand [source: NASA]. This uniformity strongly suggests that the gas that emitted it was also highly uniform, lending even more credence to the Big Bang Theory.
The CMB is not perfectly uniform, however: Miniscule variations on the level of parts per million do exist. With highly sensitive equipment, scientists can measure these temperature differences to learn about the conditions of the early universe. This is where NASA's WMAP spacecraft comes in. Launched in 2001, the WMAP, or Wilkinson Microwave Anisotropy Probe, picks up on these differences to create a picture of radiation that can reveal the universe's early structure. With it, scientists are learning more definitively about our universe's size, matter content, age, geometry and fate [source: NASA].
While we wait for more WMAP findings, we can check out the myriad discoveries of another NASA spacecraft launched more than a decade earlier.
1. Hubble Space Telescope
On April 24, 1990, NASA launched the first space-based optical telescope into orbit in hopes of gathering some clearer pictures of the universe from a superior vantage point above the blurring effects of Earth's atmosphere. Little did they know quite how groundbreaking Hubble's discoveries would be.
Along with its 94.5-inch (2.4-meter), 1,800-pound (816-kilogram) primary reflecting mirror, Hubble utilizes a wide variety of imagers and spectrographs to take pictures and analyze light -- from ultraviolet to near infrared. Circling the Earth every 97 minutes from 353 miles (569 kilometers) above the atmosphere, Hubble has observed more than 14,000 astronomical objects and described everything from weather systems on other planets to the formation and destruction of stars [source: Interstellar Studios].
Still the largest and most versatile space-based observatory even 20 years after its launch, Hubble has obtained images of objects and phenomena never before observed, gleaning insights into the structure and evolution of the universe [source: Interstellar Studios].
Perhaps most significant, though, is the impact Hubble has had on the public. With the countless images it has captured over the years, Hubble has brought the universe into homes and schools all around the world. Like the other achievements on this list, its most lasting impact may be not in its findings about outer space, but in its ability to inspire and encourage budding young astronauts and cosmologists right here on Earth.
To view Hubble's iconic photographs or to learn even more about the cosmological achievements on this list, follow the links on the next page.
Lots More Information
- Hole in the Universe Quiz
- Cosmological Achievements Pictures
- 10 Amazing Telescopes
- Milky Way Pictures
- Physical Cosmology Puzzle
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- Barnbaum, Cecilia. "Hubble Space Telescope." World Book Online Reference Center. 2004. (August 30, 2010)http://www.nasa.gov/worldbook/hubble_telescope_worldbook.html
- Dine, Michael. "Relativity." World Book Online Reference Center. 2004. (August 31, 2010)http://www.nasa.gov/worldbook/relativity_worldbook.html
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- Russell, Randy. "Astronomy Timeline." Windows to the Universe. May 6, 2008. (August 30, 2010)http://www.windows2universe.org/the_universe/uts/timeline.html
- Space Telescope Science Institute. "HubbleSite.org." (August 30, 2010)http://hubblesite.org/
- University of Illinois. "Putting Relativity to the Test." Nov. 22, 1995. (August 30, 2010)http://archive.ncsa.illinois.edu/Cyberia/NumRel/EinsteinTest.html
- University of Tennessee Dept. of Physics and Astronomy. "The Solar System." (August 30, 2010)http://csep10.phys.utk.edu/astr161/lect/index.html
- Van Helden, Albert. "The Galileo Project: Science." August 4, 2003. (August 30, 2010)http://galileo.rice.edu/science.html