Astronomers and Their Tools - Content
- Ancient Astronomers
- Astronomy in the Middle Ages
- Technological Advances
- Space Age Astronomy
- Space Race Achievements
- Canada's Role in Space Science
- Prominant Canadian Astronomers
1. Ancient Astronomers
The night sky has fascinated the human race since the dawn of time. Ancient civilizations studied the stars and their motions in attempts to understand our place in the universe, and there are many historical man-made structures which signify our past interest in the sky. Two of the best known structures are the Egyptian Pyramids and Stonehenge in England, both of which are thought to have scientific connections and were exceptional architectural designs for their time. The Pyramids were built thousands of years ago, and appear to have many connections to the stars in the night sky. The three Great Pyramids are in the exact same alignment as the three belt stars of Orion, and their faces are aligned exactly north-south and east-west. There are also linear entrance passages within the pyramids which line up precisely with important stars in the sky. Stonehenge was constructed of 56 individual segments and was possibly used as a method of determining several astronomical events. The pillars may have been constructed so that the alignment of the Sun, with respect to the pillars, would allow astronomers to determine the beginnings and the mid-points of the seasons. Stonehenge may also have been used as a tool to determine the position of the Moon throughout the year, roughly predicting the occurrence of eclipses.
During the first millennium B.C. astronomy became more scientific. Middle Eastern and Chinese cultures observed the stars and the planets more precisely, attempting to learn more about our position in the universe. They studied intently the rise and set times of the stars and planets, and developed calendars useful for agriculture. Star positions also became important tools in understanding directions and aided navigation. The most mathematically influential society during this time period was ancient Greece. The Greeks were not always correct in their beliefs; not only did they think that the Earth was the centre of the universe, but a Greek philosopher said in 434 B.C. that the Sun was a ball of fire 60 kilometres in diameter, hovering 6500 kilometres above Earth's surface. The Greeks, however, used mathematics to estimate the circumference of the Earth and developed extensive star catalogues. Around 130 B.C., Ptolemy wrote Almagest, a huge collection of astronomical data including mathematical models, information about eclipses, and planetary and stellar positions and movements. It remained the main astronomical almanac for hundreds of years, and was not seriously challenged until Copernicus disputed the geocentric model of the solar system in the 1500's.
2. Astronomy in the Middle Ages
A quiet period occurred in astronomical research after the fall of the Greek Empire, few theories being introduced for over a thousand years. During this stagnant period, most astronomical research was conducted either by the Roman Catholic Church or by astrologers. The Church employed astronomers to study the heavens. They had a firm philosophy about the objects in the night sky, believing that the Earth was the centre of the universe and that the sky was static and unchanging. In contrast to the Church was astrology, the study of the relationship between the planets and the stars and their effect on our lives. Astrology depended on supernatural beliefs rather than on scientific findings, but the research of ancient astrologers greatly benefited the scientific field of astronomy. Astrologers observed and recorded the motions of the stars and the planets with great detail, giving astronomers valuable information about their motions. Although the Church held fast to its erroneous beliefs and astrologers' information was used for supernatural philosophy, the research of both contributed significantly to astronomical advances.
By the 16th century, the tools used to measure stellar positions gave very accurate results, and astronomers began to note irregularities in the accepted model of the solar system and the night sky. In the early 1500s, Nicolaus Copernicus noted that the planets had slight discrepancies between their observed and presumed positions. The theory that the planets orbited the Earth in perfectly circular orbits could not account for the observed motions, and Copernicus speculated that the Sun was the centre of the solar system. This heliocentric model had been postulated in the third Century B.C., but had not been taken seriously and was ignored. In 1572 another astronomer, Tycho Brahe, observed a supernova explosion in the constellation of Cassiopeia. This "new star" proved that the sky was not permanent and unchanging. Both of these observations were seen as sacrilege by the Church because they went against accepted dogma. Their later published works were not officially recognized by the Church, and they were forced to renounce their heliocentric theories.
The breakthrough for astronomy came with the invention of the telescope. The spyglass was invented in 1608, but an Italian named Galileo Galilei was the first to construct a telescope in 1610 and use it to look at the night sky. His small handheld refractor telescope did not provide sharp images and had a magnification of only 20 times (similar to modern binoculars), but what Galileo saw was unlike anything anyone had ever seen before. Over the first few months of observations Galileo had discovered more about the solar system and the universe than anyone had previously achieved. He first studied the Sun and Moon and discovered their surfaces were not perfect. The Moon had numerous craters and mountains, while there were visible "blemishes" which rotated around the surface of the Sun. He observed the planets and noted that they were circular disks and not pinpoints of light like the stars. The phases of Venus were discovered and signified that planets shone by reflected sunlight. He also noticed the rings of Saturn (although he did not realize what they were) and the four large moons of Jupiter which are now named after him. The motion of the four satellites from one side of the planet to the other convinced Galileo that they were in orbit around Jupiter, proving that not every object in the sky was in orbit around the Earth. Galileo noted that there were many more stars visible through the telescope than with the naked eye, and the cloudy haze of the Milky Way was made up of thousands of faint individual stars not visible with the naked eye. Galileo's observations resulted in his excommunication from the Roman Catholic Church, as they suggested that the objects in the night sky were not perfect in form, were in constant change, and were more numerous than previously believed. While Galileo's findings revolutionized astronomy as a science and began the fall of the Church's astronomical beliefs, it was not until Kepler and Newton backed the observations with mathematical calculations that the heliocentric model of the solar system was accepted as truth.
3. Technological Advances
While Galileo was making his breakthrough observations, Johannes Kepler used the accurate recorded observations of Brahe to develop a new planetary model, and formulated the three laws of planetary motion. Essentially, the first law stated that the planets orbited the Sun in an ellipse, the second that the orbital speed of a planet slows down the further it is from the Sun, and the third gave a mathematical relationship between a planet's orbital period and its distance from the Sun. These simple but innovative laws were in agreement with the observed planetary movements, and allowed astronomers to calculate the distances from the planets to the Sun.
Lord Rosse's Telescope
© David Woodward
In the late 1600s a mathematician named Sir Isaac Newton developed his own three laws of motion involving forces, along with the universal law of gravity. His proposal of the law of gravity was a monumental concept and explained how the planets remained in orbit around the Sun. The theory of gravity finally convinced astronomers that the Sun was the centre of the solar system and governed the motions of the planets.
By the 18th century, the mathematical equations necessary to explain planetary motion had been derived, but the universe was still not fully understood. In an attempt to better understand the universe, astronomers strove to build bigger and better telescopes. Telescopes grew larger, better optics generated clearer views, and mounts improved stability for steady images. As the quality of telescopes improved, so did the images of the sky. The size of the lens in a refractor telescope was limited, however, as larger lenses produced distorted images because the lens would deform under its own weight. The development of a new telescope, the Newtonian reflector, used mirrors at the bottom of the telescopic tube instead of lenses at the top, and allowed telescopes to grow in size during the 1700's, with mirror diameters of one metre across.
With larger telescopes came a higher image resolution and greater light gathering power, giving astronomers clearer images and allowing them to probe deeper into the universe. Many deep sky objects were observed and recorded in the 18th and 19th centuries by comet hunters. Their search was not for scientific reasons; it was so as to have a reference list to avoid confusion when searching the skies for comets. The most famous lists were composed by Charles Messier and J.L.E. Dreyer. Messier's list of 110 objects contains many of the finest deep sky objects, and is still used to designate many of them. A more extensive catalogue of 7840 objects was published by Dreyer in 1888, and is known as the New Galactic Catalogue, which now contains 7790 objects. The Andromeda Galaxy is also known as M31 and NGC 224.
Telescopes were not advanced enough to show much detail in these deep sky objects, and they appeared as fuzzy patches of grey light. These patches were called nebulae, and their nature was not fully realized by astronomers. They were thought to be relatively close to the Earth, and although several of the observed "nebulae" were actually galaxies, it was unknown at the time. By the mid 1800's, the largest telescope in the world was a reflector with a mirror 183 centimetres across. Using this telescope, Lord Rosse of Ireland observed that several "nebulae" exhibited a spiral structure. It had been proposed 100 years earlier that many of these nebulae were actually island universes (now called galaxies), and Lord Rosse reiterated this belief. Astronomers remained divided over the possibility of island universes, however, and the issue remained unsettled until Edwin Hubble was able to estimate the distance to the Andromeda galaxy in 1923. He observed a certain kind of variable star which has a regular relationship between its luminosity and period, and using this relationship, estimated the Andromeda Galaxy was about 2.2 million light years away. Astronomers finally realized that many of the supposed "nebulae" were indeed island universes, or galaxies.
Telescopes continued to grow in size, and after several years the Hale 200 inch (5 metre) reflector was erected on Mt. Palomar, San Diego, CA, in 1948. This telescope was the main observing telescope in the world for years. The construction of mirrors larger than the Hale telescope encountered problems, as the mirrors became so heavy they would sag and distort under their own weight. The newest and largest telescopes in the world have a collection of hexagonal mirrors, which are combined to produce a mirror equivalent of a larger aperture. Today, the world's largest telescopes are the Keck I and II telescopes in Hawaii. They are constructed of 36 individual mirrors measuring 1.8 metres across, giving the telescope a mirror with an effective diameter of 10 metres.
The first attempt to photograph the night sky came in the late 1800s. The quality of the film was very poor, the images no better than looking through the eyepiece of a telescope. Astronomers did, however, realize that by leaving the shutter open for lengthy periods of time, film could record fainter details than were observable with the eye. When film was first used for astrophotography, it only recorded one out of every 300 incoming photons, making the film very inefficient. Over the next hundred years, film became more sensitive and a photographic plate could record about 1 of every 20 photons. Despite its inefficiency, photography was much more effective than observing through the telescope and it became the primary method of studying the sky. Faint objects showed up on long exposure photographs, and photographic plates of the same star field could be compared nightly to search for any differences or changes; this is how most asteroids were discovered, as well as Pluto in 1930.
Despite the advantages of photographing the night sky, film was only registering 5% of the incoming light, and soon computer technology revolutionized astrophotography. In 1978 the first charge-coupled device (CCD) was used in place of film. A CCD is essentially a sensitive digital camera attached to a telescope, and records up to 90% of the incoming light. All of the major telescopes in the world are now equipped with CCD's, allowing astronomers to obtain detailed images of the sky. Because a CCD produces a computer image, the images are also easily manipulated using computer programs, and can be combined to generate even more detailed and clear images.
4. Space Age Astronomy
The atmosphere limits the capabilities of Earth-based telescopes. It produces turbulence, which causes images to shimmer and twinkle. Particles in the air produce airglow, which causes the background sky never to be completely black. On the darkest nights, the background sky appears to glow at 25th magnitude, meaning objects fainter than this are undetectable. Even Sir Isaac Newton realized that the capabilities of a telescope were limited to the atmosphere, and the only way to get perfect images would be to get above the atmosphere. As soon as the space age began, astronomers dreamed of putting a telescope in orbit above the Earth. The Hubble Space Telescope (HST) went into orbit on the Space Shuttle in 1990, but the anticipation soon turned to disappointment. The HST cost more than every major observatory on the Earth combined, but an error in grinding the mirror produced blurred images. The diameter of the main mirror is 2.4 metres across, and it was ground 2 microns too flat, one 50th the width of a human hair. After spending millions of additional money to correct the error, Hubble began to produce incredible images. The HST has a limiting magnitude of 29, a billion times fainter than can be seen with the naked eye. It can perceive objects about 30 times fainter than the largest Earth-based telescopes and has a resolution nearly 15 times better. The Hubble Space Telescope has produced some of the most amazing images of our universe, and has given astronomers valuable information about everything from the solar system and the birth and death of stars to the beginnings of the universe.
The largest Earth-based telescopes are currently four times the size of the Hubble Space Telescope, but are limited because they have to look through the atmosphere. New technologies, however, have allowed Earth-based telescopes to compete with Hubble. Adaptive optics is a method of measuring the turbulence in the atmosphere using a computer, then continuously deforming the mirror slightly to correct for the turbulence. An 8-metre telescope using adaptive optics has 6400 actuators which deform the mirror hundreds of times every second. This technology is relatively new, but has already produced images which rival HST's for clarity.
Although visible light is only one form of radiation given off by stars, there are telescopes capable of detecting other forms. Because objects in the universe emit energy in many forms, an object is not always perceivable in visible light. It can be advantageous to study the sky in other wavelengths, as some objects which are invisible in the optical wavelengths emit an enormous amount of energy in other wavelengths. There are also objects located behind obscuring gas and dust, such as the Galactic centre, which are not optically visible but can be detected because energy in other forms is unaffected. Radio telescopes are huge dishes that were first constructed in the 1950's. Radio waves are longer than optical waves, and are not as easily deflected by obscuring particles. Because of this, radio waves travel through planetary clouds or dust particles in the interstellar medium. Radio telescopes are used to image planetary surfaces hidden beneath thick clouds, and can determine the presence of background stars located behind dark nebulae. Other wavelengths of radiation are often deflected by the Earth's atmosphere, and most are not detectable unless observed from space. Infrared radiation is observable minimally from the Earth, but is better studied from above the Earth's atmosphere, displaying the warmth of interstellar gases. High energy astronomy includes the observation of X-rays and gamma rays and must be observed from space, as this radiation does not reach the surface of the Earth. X-ray telescopes have been used to strengthen the theory of black holes inhabiting the centre of galaxies, while gamma ray telescopes have been used to detect and study bursts of energy in distant galaxies.
5. Space Race Achievements
While telescopes gave valuable information about our solar system and the universe, the space race opened a whole new realm of possibilities. Numerous space probes have flown by or landed on objects in our solar system, and orbiting satellites and telescopes now have clear and unobstructed views of the universe. The space age began in 1957 when the former Soviet Union launched Sputnik 1, the first artificial satellite. Four years later the first human travelled into space, a Soviet named Yuri Gagarin. With space craft being launched into orbit, scientists and astronomers dreamed of sending probes to other bodies in the solar system to obtain detailed views of their surfaces. The Moon was the obvious first target, and ten years after reaching the Moon with a spacecraft, man set foot on its surface during the historic Apollo 11 mission in July of 1969. Over the next three and a half years, six American missions successfully landed on the Moon and through surface experiments and collections of rock samples, our knowledge of the Moon increased dramatically.
The proximity of Venus made it our first planetary target, reached by a spacecraft for the first time in 1962. In 1970, the probe Venera 7 successfully landed on the surface of Venus and transmitted data for a few seconds before malfunctioning due to the planet's extreme conditions. Launched in 1978, the Pioneer Venus probe used radar to map over 90% of the previously unknown surface of Venus. The NASA Magellan project arrived at Venus in 1990 and spent four years using radar to obtain more detailed and accurate images. The more distant trip to Mars presented greater difficulties, and was first achieved in 1976. Because of the Earth-like qualities and the constant debate about the possibility of life forms in the past, Mars has now been visited by more spacecraft than any other planet. The first probes to land on its surface were the highly successful Viking missions. Viking 1 and 2 were the culmination of several early missions of flybys and orbital missions, and after eight-month journeys, the probes finally landed on the surface. The Viking Project was a complete success, transmitting valuable data from the surface for several years. The Viking Landers provided scientists with over 4000 photos from the surface and contributed a huge amount of information regarding the soil and surface conditions.
After the Viking Project, there were no American missions to Mars until the early 1990's. Several spacecraft have traveled to Mars in the past ten years; some, such as the Mars Pathfinder, have been very successful. In recent years however, NASA has also suffered setbacks with the loss of two Mars-bound probes due to miss calculations on the part of mission controlers. The first probes to travel through the asteroid belt were the two Pioneer probes, launched in the early 1970's. Pioneer 10 was the first probe to visit Jupiter and Pioneer 11 was the first to reach Saturn. NASA's second project to the outer solar system, however, was much more successful.
Voyager 1 and 2 were launched in 1977 and utilized a rare alignment of the gaseous planets to swing from one planet to the next, using their gravity as propulsion. The probes increased their speeds by about 60,000 kilometres per hour with each planetary gravity assist. Without this gravity assist method, a trip to Neptune would require about 30 years, but took only 12 with Voyager 2. Both Voyager probes were only expected to study Jupiter and Saturn, but engineers sent Voyager 2 on a trajectory which allowed the option of continuing on to Uranus and Neptune. Both craft flew by Jupiter in 1979, with Voyager 1 ending its primary mission after a flyby of Saturn in 1980. Voyager 2 passed by Saturn in 1981, and then funding was provided to keep the craft in operation during its flyby of Uranus in 1986 and Neptune in 1989. In addition to their primary mission exploring the outer planets, the spacecraft are still in operation and have now begun their second mission, known as the Voyager Interstellar Mission. Both spacecraft will remain in operation for about 20 years and will study particles from the solar wind while searching for the boundary between the solar wind and interstellar space. Despite the probes' current speed of 60,000 kilometres per hour, they will not reach the nearest stars for at least another 80,000 years. The Voyager Project was extremely successful: Voyager 2 was 100 kilometres off target after a 7 billion kilometre journey, the equivalent of sinking a hole-in-one from 3630 kilometres away. The project also provided monumental images and data on the four gaseous planets and 48 of their satellites. Much of our knowledge of the outer planets has been due to the Voyager Project. Jupiter has since been visited by the Galileo probe in 1995, and the Cassini probe, which was launched in 1997 is scheduled to arrive at Saturn in 2004. Other probes have traveled to comets and minor planets as well, including a flyby of Halley's Comet in 1986 by the Giotto probe and two flybys of asteroids in 1991 and 1994 by the Galileo probe.
6. Canada's Role in Space Science
Canada's role in the study of the universe has been limited, but important nonetheless. The Dominion Radio Astrophysical Observatory (DRAO) in Penticton, B.C. includes some of Canada's most important telescopes. The site boasts an array of seven radio telescopes and also has a 26 metre radio telescope. These are used for the Canadian Galactic Plane Survey (CGPS) along with other important astronomical research. The CGPS is a project which observes the galactic plane at various wavelengths in the radio portion of the spectrum in order to improve our understanding of the interstellar medium. Our country has also contributed to many international projects, often in collaboration with the United States. The observatory most used by professional Canadian astronomers is the Canada-France-Hawaii Telescope in Hawaii. The CFHT is a 3.6 metre state of the art telescope used for valuable research by astronomers. Canadians have contributed to the construction of two new telescopes located in the Chilean Andes, called the Gemini telescopes. These telescopes are among the most technically advanced in the world, and their 8 metre mirrors equipped with adaptive optics will provide Canadian astronomers with the best available tools to conduct their research. Canada has also participated in space exploration, conducting various experiments on the Space Shuttle and the Russian space station Mir, as well as launching numerous satellites which have studied the Earth and its weather patterns. Our nation has satellites which measure pollution in the atmosphere, atmospheric chemistry and ozone depletion. Because of our location on the Earth, Canada experiences the best auroral displays in the world and has had several satellites designed to study the science behind the displays. A Canadian instrument called the Thermal Plasma Analyzer is currently traveling to Mars on a Japanese spacecraft designed to study the Martian atmosphere. The first Canadian in space was Marc Garneau aboard the Space Shuttle Challenger in 1984, and Roberta Bondar was the second Canadian and first woman in space aboard the Space Shuttle Discovery in 1992.
|Telescope Canada-France-Hawaii||Telescopes Gemini|
Canada's most important role has been its commitment to the development of the International Space Station. Our nation signed an international agreement in 1986 to become a full partner in the International Space Station program. The ISS is currently under construction while in orbit around the Earth, and will be home to various scientific experiments and observations. Its construction would not be possible without the contribution from Canada. Canada is providing a system of robotic devices used to manoeuvre equipment outside the Station, essential for the assembly of the ISS. This system is known as the Mobile Servicing System (MSS), and consists of three parts. The main component is the Space Station Remote Manipulator System (SSRMS), also known as Canadarm2 which was installed on the ISS in 2001 by Canadian astronaut Chris Hadfield. It is an advanced device used to capture and transport equipment around the outside of the Station, and will be used to help in the assembly and maintenance of the ISS. The first Canadarm was deployed with the Space Shuttle in 1981 and will remain in use on the ISS, working in conjunction with its newer companion. Canadarm2 is more sophisticated: it is larger, can support heavier loads, and is not anchored at either end so it can travel around the Station inching along like a worm.
|MIR Space Station||International Space Station||Canadarm||Canadarm2|
In addition to the Canadarm2, the MSS is composed of the Mobile Remote Servicer Base System (MBS), scheduled for launch in May of 2002, and the Special Purpose Dextrous Manipulator (SPDM), also known as Dextre, which is scheduled for launch in 2007. The MBS is a mobile platform which supports Canadarm2, and the SPDM is a dual-armed robot which will be connected to the Canadarm2 and will be used to manoeuvre delicate objects. The Canadian Mobile Servicing System will be utilized on every missions. Because of the contribution to the ISS, Canada is entitled to use the Station for scientific experiments, and is in fact already utilizing the Station for this purpose.
7. Prominent Canadian Astronomers
Since the turn of the 20th century, Canadian astronomers have played an important role in the study of the universe. From astronomy education to the discoveries of comets and research of late-stage stellar evolution, Canadians have been and remain actively involved in the science of Astronomy. For more information, click on the link below to learn more about just a few Canadian astronomers (both professional and amateur) and the contributions they have made to their field in Canada and around the world.
The study of the universe has come a long way since the ancient civilizations who viewed the sky with wonder and confusion. The motions of the stars have been understood for centuries, but the scientific explanations and mathematical models were more difficult to understand. In the 16th century, mathematics evolved sufficiently to allow astronomers a correct determination of our presence in the solar system.
The universe is far more complex than the solar system, of course, and before the invention of the telescope the full extent of the universe was virtually unknown to astronomers. With increased size and improved optics, telescopes began to reveal more of our universe. Catalogues of deep sky objects were created, but the nature of the objects was unknown until the 20th century. Galaxies were finally understood as distant collections of billions of separate stars, and our place in the Milky Way was discovered. Telescopes are now incredibly technical, with mirrors 10 metres across, adaptive optics systems which correct for turbulence, and an orbiting telescope worth billions of dollars.
Space probes traveling to other bodies in the solar system have provided scientists an immense amount of information undetectable by telescopes. Numerous missions to the Moon, Venus and Mars have helped scientists understand the chemical composition and atmospheric conditions of these objects. The Pioneer missions and especially the Voyager Project have returned thousands of detailed photographs of the outer gaseous planets and many of their satellites. Without these probes, the outer planets would not be appreciated as they are, and the surfaces of many of their satellites would still remain unknown.
The International Space Station (ISS), a space craft in orbit around the Earth, is home to various astronauts and scientific experiments. Canada has provided the Mobile Servicing System, including Canadarm2, which has been and will be essential in the assembly of the ISS. Several Canadian astronauts have had the good fortune to travel into space, and have conducted numerous experiments on behalf of our country aboard the Space Shuttle, Mir and the ISS studying the Earth, the human body and animals.
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