Ole Rømer
Encyclopedia
Ole Christensen Rømer was a Danish astronomer
who in 1676 made the first quantitative measurement
s of the speed of light
. In scientific literature alternative spellings such as "Roemer", "Römer", or "Romer" are common.
Rømer was born on 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 the Danish island of Rømø
, to distinguish himself from a couple of other people named Christen Pedersen. 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.
Rømer was employed by the French government: Louis XIV
made him tutor for the Dauphin, and he also took part in the construction of the magnificent fountain
s at Versailles
.
In 1681, 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.
In Rømer's position as royal mathematician, he introduced the first national system for weights and measures in Denmark on 1 May 1683. 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 BE 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
of 24,000 Danish feet (circa 7,532 m).
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. 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.
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.
Roemer died at the age of 65 in 1710.
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.
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
, 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.
Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed. In 1672 Rømer went to Paris and continued observing the satellites of Jupiter as Cassini's assistant. Rømer added his own observations to Cassini's and observed that times between eclipses (particularly those of Io) got shorter as Earth approached Jupiter, and longer as Earth moved farther away. Cassini made an announcement to the Academy of Sciences on 22 August 1676:
Oddly, Cassini seems to have abandoned this reasoning, which Rømer adopted and set about buttressing in an irrefutable manner, using a selected number of observations performed by Picard and himself between 1671 and 1677. Rømer presented his results to the French Academy of Sciences
, and it was summarised soon after by an anonymous reporter in a short paper, , published 7 December 1676 in the Journal des sçavans
. Unfortunately the paper bears the stamp of the reporter failing to understand Rømer's presentation, and as the reporter resorted to cryptic phrasings to hide his lack of understanding, he obfuscated Rømer's reasoning in the process. Unfortunately Rømer himself never published his results.
Assume the Earth is in L, at the second quadrature
with Jupiter (i.e. ALB is 90°), and Io emerges from D. After several orbits of Io, at 42.5 hours per orbit, the Earth is in K. Rømer reasoned that if light is not propagated instantaneously, the additional time it takes to reach K, that he reckoned about 3½ minutes, would explain the observed delay. Rømer observed immersions in C from the symmetric positions F and G, to avoid confusing eclipse
s (Io shadowed by Jupiter from C to D) and occultation
s (Io hidden behind Jupiter at various angles). In the table below, his observations in 1676, including the one on August 7, believed to be in opposition H, and the one observed at Paris Observatory
to be 10 minutes late, on November 9.
By trial and error
, during eight years of observations Rømer worked out how to account for the retardation of light when reckoning the ephemeris
of Io. He calculated the delay as a proportion of the angle corresponding to a given Earth's position with respect to Jupiter, Δt=22*[minutes] . When the angle α is 180° the delay becomes 22 minutes, which may be interpreted as the time necessary for the light to cross a distance equal to the diameter of the Earth's orbit, H to E. (Actually, Jupiter is not visible from the conjunction point E.) That interpretation makes it possible to calculate the strict result of Rømer's observations: The ratio of the speed of light to the speed with which Earth orbits the sun, which is the ratio of
the duration of a year divided by pi as compared to the 22 minutes
≈ 7,600.
In comparison the modern value is circa ≈ 10,100.
Rømer neither calculated this ratio, nor did he give a value for the speed of light. However, many others calculated a speed from his data, the first being Christiaan Huygens; after corresponding with Rømer and eliciting more data, Huygens deduced that light travelled Earth diameters per second.
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.
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. The modern value is 8 minutes and 19 seconds, and a speed of 299,792.46 km/s.
A plaque at the Observatory of Paris, where the Danish astronomer happened to be working, commemorates what was, in effect, the first measurement of a universal quantity made on this planet.
, the Altazimuth and the Passage Instrument.
, 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 has been a part of the museum Kroppedal
at the same location.
as a gentleman under Denmark.
In the 1960s, the comic-book superhero The Flash on a number of occasions would measure his velocity in "Roemers" [sic], in honour of Ole Rømer's "discovery" of the speed of light
.
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
who in 1676 made the first quantitative measurement
Measurement
Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the metre, second or degree Celsius...
s of the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
. In scientific literature alternative spellings such as "Roemer", "Römer", or "Romer" are common.
General biography
Alderman
An alderman is a member of a municipal assembly or council in many jurisdictions founded upon English law. The term may be titular, denoting a high-ranking member of a borough or county council, a council member chosen by the elected members themselves rather than by popular vote, or a council...
. Christen Pedersen had taken to using the name Rømer, which means that he was from the Danish island of Rømø
Rømø
Rømø is a Danish island in the Wadden Sea. Rømø is part of Tønder municipality. The island has 650 inhabitants as of 1 January 2011 and covers an area of 129 km². Rømø is a popular tourist spot each year....
, to distinguish himself from a couple of other people named Christen Pedersen. There are few sources on Ole Rømer until his immatriculation in 1662 at the University of Copenhagen
University of Copenhagen
The University of Copenhagen is the oldest and largest university and research institution in Denmark. Founded in 1479, it has more than 37,000 students, the majority of whom are female , and more than 7,000 employees. The university has several campuses located in and around Copenhagen, with the...
, at which his mentor was Rasmus Bartholin
Rasmus Bartholin
Rasmus Bartholin was a Danish scientist and physician. As part of his studies, he travelled in Europe for ten years. Professor at the University of Copenhagen, first in Geometry, later in Medicine...
who published his discovery of the double refraction of a light ray by Iceland spar (calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
) in 1668, while Rømer was living in his home. Rømer was given every opportunity to learn mathematics and astronomy using Tycho Brahe
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...
's astronomical observations, as Bartholin had been given the task of preparing them for publication.
Rømer was employed by the French government: Louis XIV
Louis XIV of France
Louis XIV , known as Louis the Great or the Sun King , was a Bourbon monarch who ruled as King of France and Navarre. His reign, from 1643 to his death in 1715, began at the age of four and lasted seventy-two years, three months, and eighteen days...
made him tutor for the Dauphin, and he also took part in the construction of the magnificent fountain
Fountain
A fountain is a piece of architecture which pours water into a basin or jets it into the air either to supply drinking water or for decorative or dramatic effect....
s at Versailles
Versailles
Versailles , a city renowned for its château, the Palace of Versailles, was the de facto capital of the kingdom of France for over a century, from 1682 to 1789. It is now a wealthy suburb of Paris and remains an important administrative and judicial centre...
.
In 1681, Rømer returned to Denmark and was appointed professor of astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
at the University of Copenhagen, and the same year he married Anne Marie Bartholin, the daughter of Rasmus Bartholin
Rasmus Bartholin
Rasmus Bartholin was a Danish scientist and physician. As part of his studies, he travelled in Europe for ten years. Professor at the University of Copenhagen, first in Geometry, later in Medicine...
. He was active also as an observer, both at the University Observatory
Observatory
An observatory is a location used for observing terrestrial or celestial events. Astronomy, climatology/meteorology, geology, oceanography and volcanology are examples of disciplines for which observatories have been constructed...
at Rundetårn
Rundetårn
The Rundetårn is a 17th-century tower located in central Copenhagen, Denmark. One of the many architectural projects of Christian IV, it was built as an astronomical observatory...
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
Copenhagen Fire of 1728
The Copenhagen Fire of 1728 was the largest fire in the history of Copenhagen, Denmark. It began on the evening of October 20, 1728, and continued to burn until the morning of October 23. It destroyed approximately 28% of the city , left 20% of the population homeless, and the reconstruction lasted...
. However, a former assistant (and later an astronomer in his own right), Peder Horrebow
Peder Horrebow
Peder [Nielsen] Horrebow was a Danish astronomer. Born in Løgstør, Jutland to a poor family of fishermen, Horrebow entered the University of Copenhagen in 1703. He worked his way through grammar school and university by virtue of his technical knowledge: he repaired mechanical and musical...
, loyally described and wrote about Rømer's observations.
In Rømer's position as royal mathematician, he introduced the first national system for weights and measures in Denmark on 1 May 1683. 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 BE an excellent degree of accuracy. His goal was to achieve a definition based on astronomical constants, using a pendulum
Pendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...
. This would happen after his death, practicalities making it too inaccurate at the time. Notable is also his definition of the new Danish mile
Danish units of measurement
The Danes started with a system of units based on a Greek pous of which they picked up through trade in the late Bronze Age/early Iron Age. Some early standards of measure can be recovered from measured drawings made of the , which though dating to the early Iron Age exemplifies plank built...
of 24,000 Danish feet (circa 7,532 m).
In 1700, Rømer managed to get the king to introduce the Gregorian calendar
Gregorian calendar
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...
in Denmark-Norway — something Tycho Brahe
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...
had argued for in vain a hundred years earlier.
Rømer also developed one of the first temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
scales. Fahrenheit visited him in 1708 and improved on the Rømer scale
Rømer scale
Rømer is a temperature scale named after the Danish astronomer Ole Christensen Rømer, who proposed it in 1701.In this scale, the zero was initially set using freezing brine. The boiling point of water was defined as 60 degrees...
, the result being the familiar Fahrenheit
Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...
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
Police
The police is a personification of the state designated to put in practice the enforced law, protect property and reduce civil disorder in civilian matters. Their powers include the legitimized use of force...
, 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.
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.
Roemer died at the age of 65 in 1710.
Rømer and the speed of light
The determination of longitudeLongitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
is a significant practical problem in cartography
Cartography
Cartography is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.The fundamental problems of traditional cartography are to:*Set the map's...
and navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
.
Philip III of Spain
Philip III of Spain
Philip III , also known as Philip the Pious, was the King of Spain and King of Portugal and the Algarves, where he ruled as Philip II , from 1598 until his death...
offered a prize for a method to determine the longitude of a ship out of sight of land, and
Galileo
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
proposed a method of establishing the time of day, and thus longitude, based on the times of the eclipses of the moons of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, 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
Uraniborg
Uranienborg was a Danish astronomical observatory operated by Tycho Brahe; built circa 1576-1580 on Hven, an island in the Øresund between Zealand and Scania, which at that time was part of Denmark. The observatory was shortly after its construction expanded with an underground facility,...
on the island of Hven
Hven
Ven is a small Swedish island in the Öresund strait, between Scania and Zealand . It is situated in Landskrona Municipality, Skåne County. The island has 371 inhabitants and an area of . During the 1930s, the population was at its peak, with approximately 1,300 inhabitants...
, near Copenhagen, in 1671. Over a period of several months, Jean Picard
Jean Picard
Jean-Felix Picard was a French astronomer and priest born in La Flèche, where he studied at the Jesuit Collège Royal Henry-Le-Grand. He was the first person to measure the size of the Earth to a reasonable degree of accuracy in a survey conducted in 1669–70, for which he is honored with a...
and Rømer observed about 140 eclipses of Jupiter's moon Io
Io (moon)
Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....
, while in Paris Giovanni Domenico Cassini
Giovanni Domenico Cassini
This article is about the Italian-born astronomer. For his French-born great-grandson, see Jean-Dominique Cassini.Giovanni Domenico Cassini was an Italian/French mathematician, astronomer, engineer, and astrologer...
observed the same eclipses. By comparing the times of the eclipses, the difference in longitude of Paris to Uranienborg was calculated.
Cassini had observed the moons of Jupiter between 1666 and 1668, and discovered discrepancies in his measurements that, at first, he attributed to light having a finite speed. In 1672 Rømer went to Paris and continued observing the satellites of Jupiter as Cassini's assistant. Rømer added his own observations to Cassini's and observed that times between eclipses (particularly those of Io) got shorter as Earth approached Jupiter, and longer as Earth moved farther away. Cassini made an announcement to the Academy of Sciences on 22 August 1676:
This second inequality appears to be due to light taking some time to reach us from the satellite; light seems to take about ten to eleven minutes [to cross] a distance equal to the half-diameter of the terrestrial orbit.
French Academy of Sciences
The French Academy of Sciences is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research...
, and it was summarised soon after by an anonymous reporter in a short paper, , published 7 December 1676 in the Journal des sçavans
Journal des sçavans
The Journal des sçavans , founded by Denis de Sallo, was the earliest academic journal published in Europe, that from the beginning also carried a proportion of material that would not now be considered scientific, such as obituaries of famous men, church history, and legal reports...
. Unfortunately the paper bears the stamp of the reporter failing to understand Rømer's presentation, and as the reporter resorted to cryptic phrasings to hide his lack of understanding, he obfuscated Rømer's reasoning in the process. Unfortunately Rømer himself never published his results.
Assume the Earth is in L, at the second quadrature
Quadrature (astronomy)
In astronomy, quadrature is that aspect of a heavenly body in which it makes a right angle with the direction of the Sun. It is applied especially to the apparent position of a superior planet, or of the Moon at first and last quarters....
with Jupiter (i.e. ALB is 90°), and Io emerges from D. After several orbits of Io, at 42.5 hours per orbit, the Earth is in K. Rømer reasoned that if light is not propagated instantaneously, the additional time it takes to reach K, that he reckoned about 3½ minutes, would explain the observed delay. Rømer observed immersions in C from the symmetric positions F and G, to avoid confusing eclipse
Eclipse
An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...
s (Io shadowed by Jupiter from C to D) and occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
s (Io hidden behind Jupiter at various angles). In the table below, his observations in 1676, including the one on August 7, believed to be in opposition H, and the one observed at Paris Observatory
Paris Observatory
The Paris Observatory is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world...
to be 10 minutes late, on November 9.
| Month | Day | Time | Tide | orbits | average (hours) |
|---|---|---|---|---|---|
| May | 13 | 2:49:42 | C | ||
| 2,750,789s | 18 | 42.45 | |||
| Jun | 13 | 22:56:11 | C | ||
| 4,747,719s | 31 | 42.54 | |||
| Aug | 7 | 21:44:50 | D | ||
| 612,065s | 4 | 42.50 | |||
| Aug | 14 | 23:45:55 | D | ||
| 764,718s | 5 | 42.48 | |||
| Aug | 23 | 20:11:13 | D | ||
| 6,906,272s | 45 | 42.63 | |||
| Nov | 9 | 17:35:45 | D | ||
By trial and error
Trial and error
Trial and error, or trial by error, is a general method of problem solving, fixing things, or for obtaining knowledge."Learning doesn't happen from failure itself but rather from analyzing the failure, making a change, and then trying again."...
, during eight years of observations Rømer worked out how to account for the retardation of light when reckoning the ephemeris
Ephemeris
An ephemeris is a table of values that gives the positions of astronomical objects in the sky at a given time or times. Different kinds of ephemerides are used for astronomy and astrology...
of Io. He calculated the delay as a proportion of the angle corresponding to a given Earth's position with respect to Jupiter, Δt=22*
the duration of a year divided by pi as compared to the 22 minutes
≈ 7,600.
In comparison the modern value is circa ≈ 10,100.
Rømer neither calculated this ratio, nor did he give a value for the speed of light. However, many others calculated a speed from his data, the first being Christiaan Huygens; after corresponding with Rømer and eliciting more data, Huygens deduced that light travelled Earth diameters per second.
Rømer's view that the velocity of light was finite was not fully accepted until measurements of the so-called aberration of light
Aberration of light
The aberration of light is an astronomical phenomenon which produces an apparent motion of celestial objects about their real locations...
were made by James Bradley
James Bradley
James Bradley FRS was an English astronomer and served as Astronomer Royal from 1742, succeeding Edmund Halley. He is best known for two fundamental discoveries in astronomy, the aberration of light , and the nutation of the Earth's axis...
in 1727.
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. The modern value is 8 minutes and 19 seconds, and a speed of 299,792.46 km/s.
A plaque at the Observatory of Paris, where the Danish astronomer happened to be working, 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 circleMeridian circle
The meridian circle, transit circle, or transit telescope is an instrument for observing the time of stars passing the meridian, at the same time measuring its angular distance from the zenith...
, the Altazimuth and the Passage Instrument.
The Ole Rømer Museum
The Ole Rømer Museum is located in the municipality of Høje-TaastrupHøje-Taastrup
Høje-Taastrup Kommune is a municipality in Region Hovedstaden on the island of Zealand in eastern Denmark. The municipality covers an area of 78 km² , and has a total population of 47,158...
, 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 has been a part of the museum Kroppedal
Kroppedal
Kroppedal Museum in Denmark, from Copenhagen, was established in 2003. Kroppedal is the national museum of Danish astronomy, has a large archaeological unit, and an ethnological unit specializing in modern society...
at the same location.
Popular culture
Ole Rømer features in the game Empire: Total WarEmpire: Total War
Empire: Total War is a turn-based strategy and real-time tactics computer game developed by The Creative Assembly and published by Sega. The fifth instalment in the Total War series, the game was released in North America on 3 March 2009, and in the rest of the world the following day...
as a gentleman under Denmark.
In the 1960s, the comic-book superhero The Flash on a number of occasions would measure his velocity in "Roemers" [sic], in honour of Ole Rømer's "discovery" of the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
.
General references
- 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. MichelsonAlbert Abraham MichelsonAlbert Abraham Michelson was an American physicist known for his work on the measurement of the speed of light and especially for the Michelson-Morley experiment. In 1907 he received the Nobel Prize in Physics...
, but considers forerunners including Rømer. Also available on line: Stats.uwaterloo.ca) - Axel V. Nielsen: Ole Rømer. En Skildring af hans Liv og Gerning. København, 1944.
External links
- Roemer, Ole Christensen (at the Galileo Project)
- Obs.univ-lyon1.fr, Démonstration touchant le mouvement de la lumière (The 1676 paper on the speed of light, in old French, as ordinary text)
- 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