Rømer, Ole
Peter Duveen (talk | contribs) |
Peter Duveen (talk | contribs) |
||
| Line 29: | Line 29: | ||
==Rømer and the speed of light== | ==Rømer and the speed of light== | ||
| − | |||
The determination of [[longitude]] is a significant practical problem in [[cartography]] and [[navigation]]. | The determination of [[longitude]] is a significant practical problem in [[cartography]] and [[navigation]]. | ||
[[Philip III of Spain]] offered a prize for a method to determine the longitude of a ship out of sight of land, and | [[Philip III of Spain]] offered a prize for a method to determine the longitude of a ship out of sight of land, and | ||
[[Galileo Galilei|Galileo]] proposed a method of establishing the time of day, and thus longitude, based on the times of the eclipses of the moons of [[Jupiter]], in essence using the Jovian system as a cosmic clock; this method was not significantly improved until accurate mechanical clocks were developed in the eighteenth century. Galileo proposed this method to the Spanish crown (1616–1617) but it proved to be impractical, because of the inaccuracies of Galileo's timetables and the difficulty of observing the eclipses on a ship. However, with refinements the method could be made to work on land. | [[Galileo Galilei|Galileo]] proposed a method of establishing the time of day, and thus longitude, based on the times of the eclipses of the moons of [[Jupiter]], in essence using the Jovian system as a cosmic clock; this method was not significantly improved until accurate mechanical clocks were developed in the eighteenth century. Galileo proposed this method to the Spanish crown (1616–1617) but it proved to be impractical, because of the inaccuracies of Galileo's timetables and the difficulty of observing the eclipses on a ship. However, with refinements the method could be made to work on land. | ||
| − | After studies in Copenhagen, Rømer joined the observatory of [[Uraniborg]] on the island of [[Hven]], near Copenhagen, in 1671. Over a period of several months, [[Jean Picard]] and Rømer observed about 140 eclipses of Jupiter's moon [[Io (moon)|Io]], while in Paris [[Giovanni Domenico Cassini]] observed the same eclipses. By comparing the times of the eclipses, the difference in longitude of Paris to Uranienborg was calculated. | + | The reason why syncronized time is important to measuring longitude is that two observers, if they know they are making measurements at the same time, can measure the position of the stars with respect to the horizon, the difference in the angle between the two measurements of the same star with respect to a plane passing through the poles of the earth equalling the difference in longitude of their positions on the earth's surface. Some additional data such as the diameter of the earth would yield the distance between the two positions as well. Conversely, if the distance between the two positions could be accurately supplied, the earth's diameter could be calculated from the data. |
| + | |||
| + | After his studies in Copenhagen, Rømer joined the observatory of [[Uraniborg]] on the island of [[Hven]], near Copenhagen, in 1671. Over a period of several months, [[Jean Picard]] and Rømer observed about 140 eclipses of Jupiter's moon [[Io (moon)|Io]], while in Paris [[Giovanni Domenico Cassini]] observed the same eclipses. By comparing the times of the eclipses, the difference in longitude of Paris to Uranienborg was calculated. | ||
| + | |||
| + | Rømer noticed upon examination of the data that he collected along with the observations of Cassini that the times at which the satellite Io emerges from the shadow of Jupiter in each of its revolutions about the planet are continually lengthened as the earth recedes from Jupiter, while in a similar but reverse manner, the times between emergences are shortened as the earth approaches Jupiter. More specifically, Roemer reported to the French Academy of Sciences that between early September and the 16th of November, of the year 1676, a delay of about 10 minutes accrued. Because of the periodic nature of the disturbance, and the reversal of the phenomenon when earth approached Jupiter, Roemer was able to demonstrate that the changes could be accounted for by assuming that light had a finite velocity. | ||
| − | + | Roemer did not actually calculate the speed of light from his observations. At the time, the distance between the sun and the earth was still only a roughly calculated quantity, while the earth's circular motion meant that the distances between the earth and Jupiter did not accrue uniformly, but vary according to the time of year and the position of the earth in its orbit. It would be left to later investigators to pin down an actual speed of light based on these phenomena. Roemer appears to have been more interested in correcting tables of the revolution of Jupiter's moons for the sake of measuring longitude that he was in fixing the speed of light. His important contribution was that he recognized the true nature of the phenomenon, and quantified and predicted the observed effect on the observations of Jupiter's moons. | |
| − | + | That light had a finite speed was a finding that the scientific community resisted accepting, even though two thousand years ealier, Aristotle had contemplated the possibility of a finite speed in analogy to sound and even suggested a way of measuring it. Still, the predominent view was that the speed of light was infinite. | |
| − | + | However, many others calculated a speed from his data, the first being [[Christiaan Huygens]] in 1690.<ref>[[Christiaan Huygens|Huygens, Christian]] (8 January 1690) ''[http://www.gutenberg.org/catalog/world/readfile?fk_files=164378 Treatise on Light]''. Translated into English by Silvanus P. Thompson, Project Gutenberg etext, [http://www.gutenberg.org/catalog/world/readfile?fk_files=164378&pageno=11 p. 11]. Retrieved on 2007-04-29.</ref> | |
| − | |||
| − | Rømer's view that the velocity of light was finite was not fully accepted until measurements of the so-called [[aberration of light]] were made by [[James Bradley]] in 1727. | + | Rømer's view that the velocity of light was finite was not fully accepted until measurements of the so-called [[aberration of light]] were made by [[James Bradley]] in 1727. Bradley's observations depend on the fact that the movement of the earth around the sun distorts the actual position of any luminous body in the heavens, the distortion depending on the radio of the velocities of the earth to that of light. This causes each body such as a star to appear to transcribe a small ellipse over a period of a year. Measuring this distortion yields a value for the speed of light. Bradley's measurements were in harmony with Roemer's observations, resulting in almost universal acceptance of Roemer's original conjecture. |
In 1809, again making use of observations of Io, but this time with the benefit of more than a century of increasingly precise observations, the astronomer [[Jean Baptiste Joseph Delambre]] reported the time for light to travel from the Sun to the Earth as 8 minutes and 12 seconds. Depending on the value assumed for the astronomical unit, this yields the speed of light as just a little more than 300,000 kilometres per second. | In 1809, again making use of observations of Io, but this time with the benefit of more than a century of increasingly precise observations, the astronomer [[Jean Baptiste Joseph Delambre]] reported the time for light to travel from the Sun to the Earth as 8 minutes and 12 seconds. Depending on the value assumed for the astronomical unit, this yields the speed of light as just a little more than 300,000 kilometres per second. | ||
| − | A plaque at the Observatory of Paris, where the | + | A plaque at the Observatory of Paris, where Roemer was working at the time of his conjecture, commemorates what was, in effect, the first measurement of a universal quantity made on this planet. |
==Inventions== | ==Inventions== | ||
Revision as of 09:12, 16 September 2007
Ole Christensen Rømer[1] (25 September 1644, Århus – 19 September 1710, Copenhagen) was a Danish astronomer. In 1676, he made the first quantitative measurements of the speed of light.
General biography
Rømer was born 25 September 1644 in Århus to a merchant and skipper Christen Pedersen and Anna Olufsdatter Storm, daughter of an alderman. Christen Pedersen had taken to using the name Rømer, which means that he was from Rømø, to disambiguate himself from a couple of other people named Christen Pedersen.[2] There are few sources on Ole Rømer until his immatriculation in 1662 at the University of Copenhagen, at which his mentor was Rasmus Bartholin who published his discovery of the double refraction of a light ray by Iceland spar (calcite) in 1668 while Rømer was living in his home. Rømer was given every opportunity to learn mathematics and astronomy using Tycho Brahe's astronomical observations, as Bartholin had been given the task of preparing them for publication.[3]
Rømer was employed by the French government: Louis XIV made him teacher for the Dauphin, and he also took part in the construction of the magnificent fountains at Versailles.
In 1677, Rømer returned to Denmark and was appointed professor of astronomy at the University of Copenhagen, and the same year he married Anne Marie Bartholin, the daughter of Rasmus Bartholin. He was active also as an observer, both at the University Observatory at Rundetårn and in his home, using improved instruments of his own construction. Unfortunately, his observations have not survived: they were lost in the great Copenhagen Fire of 1728. However, a former assistant (and later an astronomer in his own right), Peder Horrebow, loyally described and wrote about Rømer's observations.
Roemer was appointed royal mathematician in 1681, and in 1883, he introduced the first national system for weights and measures in Denmark. Initially based on the Rhine foot, a more accurate national standard was adopted in 1698. Later measurements of the standards fabricated for length and volume show an excellent degree of accuracy. His goal was to achieve a definition based on astronomical constants, using a pendulum. This would happen after his death, practicalities making it too inaccurate at the time. Notable is also his definition of the new Danish mile. It was 24,000 Danish feet, which corresponds to 4 minutes of arc latitude, thus making navigation easier.
Roemer had developed a thermometer so that he could monitor the temperature and its effect on astronomical instruments. He was among the first to develop a temperature scale, dividing the temperature between of freezing water and boiling water into sixty degrees. By the early 1890s
In 1700, Rømer managed to get the king to introduce the Gregorian calendar in Denmark-Norway—something Tycho Brahe had argued for in vain a hundred years earlier.
Rømer also developed one of the first temperature scales. He divided the temperature range between freezing and boiling water into 60 degrees. Fahrenheit visited him in 1708 and improved on the Rømer scale, the result being the familiar Fahrenheit temperature scale still in use today in a few countries.
Rømer also established several navigation schools in many Danish cities.
In 1705, Rømer was made the second Chief of the Copenhagen Police, a position he kept until his death in 1710. As one of his first acts, he fired the entire force, being convinced that the morale was alarmingly low. He was the inventor of the first street lights (oil lamps) in Copenhagen, and worked hard to try to control the beggars, poor people, unemployed, and prostitutes of Copenhagen. This was the start of a social reform.[citation needed]
In Copenhagen, Rømer made rules for building new houses, got the city's water supply and sewers back in order, ensured that the city's fire department got new and better equipment, and was the moving force behind the planning and making of new pavement in the streets and on the city squares.
Rømer and the speed of light
The determination of longitude is a significant practical problem in cartography and navigation. Philip III of Spain offered a prize for a method to determine the longitude of a ship out of sight of land, and Galileo proposed a method of establishing the time of day, and thus longitude, based on the times of the eclipses of the moons of Jupiter, in essence using the Jovian system as a cosmic clock; this method was not significantly improved until accurate mechanical clocks were developed in the eighteenth century. Galileo proposed this method to the Spanish crown (1616–1617) but it proved to be impractical, because of the inaccuracies of Galileo's timetables and the difficulty of observing the eclipses on a ship. However, with refinements the method could be made to work on land.
The reason why syncronized time is important to measuring longitude is that two observers, if they know they are making measurements at the same time, can measure the position of the stars with respect to the horizon, the difference in the angle between the two measurements of the same star with respect to a plane passing through the poles of the earth equalling the difference in longitude of their positions on the earth's surface. Some additional data such as the diameter of the earth would yield the distance between the two positions as well. Conversely, if the distance between the two positions could be accurately supplied, the earth's diameter could be calculated from the data.
After his studies in Copenhagen, Rømer joined the observatory of Uraniborg on the island of Hven, near Copenhagen, in 1671. Over a period of several months, Jean Picard and Rømer observed about 140 eclipses of Jupiter's moon Io, while in Paris Giovanni Domenico Cassini observed the same eclipses. By comparing the times of the eclipses, the difference in longitude of Paris to Uranienborg was calculated.
Rømer noticed upon examination of the data that he collected along with the observations of Cassini that the times at which the satellite Io emerges from the shadow of Jupiter in each of its revolutions about the planet are continually lengthened as the earth recedes from Jupiter, while in a similar but reverse manner, the times between emergences are shortened as the earth approaches Jupiter. More specifically, Roemer reported to the French Academy of Sciences that between early September and the 16th of November, of the year 1676, a delay of about 10 minutes accrued. Because of the periodic nature of the disturbance, and the reversal of the phenomenon when earth approached Jupiter, Roemer was able to demonstrate that the changes could be accounted for by assuming that light had a finite velocity.
Roemer did not actually calculate the speed of light from his observations. At the time, the distance between the sun and the earth was still only a roughly calculated quantity, while the earth's circular motion meant that the distances between the earth and Jupiter did not accrue uniformly, but vary according to the time of year and the position of the earth in its orbit. It would be left to later investigators to pin down an actual speed of light based on these phenomena. Roemer appears to have been more interested in correcting tables of the revolution of Jupiter's moons for the sake of measuring longitude that he was in fixing the speed of light. His important contribution was that he recognized the true nature of the phenomenon, and quantified and predicted the observed effect on the observations of Jupiter's moons.
That light had a finite speed was a finding that the scientific community resisted accepting, even though two thousand years ealier, Aristotle had contemplated the possibility of a finite speed in analogy to sound and even suggested a way of measuring it. Still, the predominent view was that the speed of light was infinite.
However, many others calculated a speed from his data, the first being Christiaan Huygens in 1690.[4]
Rømer's view that the velocity of light was finite was not fully accepted until measurements of the so-called aberration of light were made by James Bradley in 1727. Bradley's observations depend on the fact that the movement of the earth around the sun distorts the actual position of any luminous body in the heavens, the distortion depending on the radio of the velocities of the earth to that of light. This causes each body such as a star to appear to transcribe a small ellipse over a period of a year. Measuring this distortion yields a value for the speed of light. Bradley's measurements were in harmony with Roemer's observations, resulting in almost universal acceptance of Roemer's original conjecture.
In 1809, again making use of observations of Io, but this time with the benefit of more than a century of increasingly precise observations, the astronomer Jean Baptiste Joseph Delambre reported the time for light to travel from the Sun to the Earth as 8 minutes and 12 seconds. Depending on the value assumed for the astronomical unit, this yields the speed of light as just a little more than 300,000 kilometres per second.
A plaque at the Observatory of Paris, where Roemer was working at the time of his conjecture, commemorates what was, in effect, the first measurement of a universal quantity made on this planet.
Inventions
In addition to inventing the first street lights in Copenhagen, Rømer also invented the Meridian circle, the Altazimuth and the Passage Instrument.
The Ole Rømer Museum
The Ole Rømer Museum is located in the municipality of Høje-Taastrup, Denmark, at the excavated site of Rømer's observatory Observatorium Tusculanum at Vridsløsemagle. The observatory operated until about 1716 when the remaining instruments were moved to Rundetårn in Copenhagen. There is a large collection of ancient and more recent astronomical instruments on display at the museum. Since 2002 this exhibition is a part of the museum Kroppedal at the same location.
Notes
- ↑ In the scientific literature, his name is alternatively spelt "Roemer," "Römer," or "Romer."
- ↑ Friedrichsen, Per and Tortzen, Chr. Gorm (2001). Ole Rømer - Korrespondance og afhandlinger samt et udvalg af dokumenter (in Danish). Copenhagen: C. A. Reitzels Forlag, p. 16. ISBN 87-7876-258-8.
- ↑ Friedrichsen; Tortzen (2001), pp. 19-20.
- ↑ Huygens, Christian (8 January 1690) Treatise on Light. Translated into English by Silvanus P. Thompson, Project Gutenberg etext, p. 11. Retrieved on 2007-04-29.
ReferencesISBN links support NWE through referral fees
- R. J. MacKay and R. W. Oldford. "Scientific Method, Statistical Method and the Speed of Light," Statistical Science 15(3):254–278, 2000. (mostly about A.A. Michelson, but considers forerunners including Rømer. Also available on line: [1])
- Axel V. Nielsen: Ole Rømer. En Skildring af hans Liv og Gerning. København, 1944.
- Moran, Jeffrey B. 2001. How do we know the laws of thermodynamics. Great scientific questions and the scientists who answered them. New York: Rosen Pub. Group. 34-39. ISBN 0823933849.
- Caes, Charles J. 2001. How do we know the speed of light. Great scientific questions and the scientists who answered them. New York: Rosen Pub. Group. 48-53. ISBN 0823933873.
- Smithsonian Institution. 1855. Annual report of the Board of Regents of the Smithsonian Institution. Washington: A.0.P. Nicholson, public printer. 141, 146-7.
External links
- Roemer, Ole Christensen (at the Galileo Project)
- ROEMER, Démonstration touchant le mouvement de la lumière (The 1676 paper on the speed of light, in French, as ordinary text)
- A Demonstration concerning the Motion of Light, communicated from Paris (The 1676 paper on the speed of light, in English and French, as images)
- Rømer and the Doppler Principle. (further details on Rømer's result)
- Fysikeren Ole Rømer (in Danish)
- Kroppedal Museum
- Ole Rømer on the 50 Danish Kroner banknote
Credits
New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:
The history of this article since it was imported to New World Encyclopedia:
Note: Some restrictions may apply to use of individual images which are separately licensed.
