Ole Rømer

Ole Christensen Rømer (born 25 Septemberjul / October 5 1644greg in Aarhus, .. † September 19, 1710 in Copenhagen), or even Ole Olaus with pros and Romans or Romans with the last name, was a Danish astronomer. His parents were Christian Olesen Rømer, a wealthy businessman with a mathematical library, and his wife Anne Marie Storm.

He became known through the first evidence that the speed of light is finite and not infinite, or through the instructions on how the speed of light can be calculated by observing the moons of Jupiter.

Life

From 1662 Rømer studied astronomy at Erasmus Bartholin in Copenhagen and worked with this until 1671 - partly due to the publication of the writings of Tycho Brahe - together. 1671 came the astronomer Jean Picard on behalf of the Paris Académie des Sciences to Copenhagen to be determined on the Øresund Hven the longitude of the old observatory of Tycho Brahe. With the determination of the difference in length between Hven and Paris (length problem), the exact tables of Tycho Brahe could also use in Paris. For this, the circulation of Jupiter's moons had to be observed. The wizard Ole Rømer helped so cleverly in this work, that he was invited to come to the end of the series in April 1672 Picard to Paris. Rømer agreed and worked as a member of the Academy at Giovanni Domenico Cassini at the Paris Observatory. He developed there in 1672 a micrometer for telescopes and built mechanical models for Planetenumläufe ( Jovilabium ( 1677), Saturnarium ( 1678), Lunarium ( 1680) ). He developed a new type of epicyclic gear. This Planetariums should facilitate the tedious astronomical observations.

1676 Rømer was appointed Royal Danish astronomer and was built in 1681 from Paris to the University of Copenhagen. There he became a professor of mathematics. In 1681 he married the daughter of Bartholin, who died in 1694 ( in 1698 he married her sister ). In 1683 he led the Kingdom of Denmark a a nationally uniform system of weights and measures. In 1700 he developed an accurate measure of star positions, the meridian circle. With him he wanted by measuring stellar parallaxes of Sirius provide conclusive evidence for the model of the solar system by Nicolaus Copernicus. The detection was achieved only in 1838 by Friedrich Wilhelm Bessel. On March 1, 1700 Denmark introduced to Romer's suggestion, the Gregorian calendar. In 1702 he built the first thermometer with two fixed points ( Rømer scale), the Fahrenheit after a visit with him ( 1708) further developed. Rømer headed about 1705 in his Adversaria ( notebook ) a measurement error formula ago for his meridian instrument. Today, this measurement error formula Tobias Mayer is attributed, who only 51 years later, in 1756, found without knowing centromere derivation. Through his close observation Rømer was able to prove that the star Castor in the constellation Gemini is a double star system. Finally, he took part in the action observation of Mercury transit of the sun on May 5, 1707 which evaluated them.

After Rømer had already held various political offices from 1688 onwards, he became mayor in 1705 in Copenhagen, head of the police and Senator. In these roles, he led a far-reaching improvements, including the first street lighting (using oil lamps), rehabilitation of water supply and sewerage. These offices he held until his death. In the Our ​​Lady's Church, he was buried.

Most of his equipment and records were destroyed in the great fire of Copenhagen on 20 October 1728 individual pieces are gathered, nor in Kroppedal Museum. His ideas were partially spread after his death by his pupil books Peder Horrebow.

The lunar crater Romans is named after him.

Speed of light

The question of whether the speed of light is finite or infinite, had been controversial for centuries. Followers of Aristotle, including René Descartes, argued for infinite speed of light. 1668 Cassini had published his first table in Bologna who reported a roadmap for the eclipses of the four moons of Jupiter. The times given there helped with the longitude problem. Starting in 1668 he had found discrepancies between the schedule and observation. From 1672 to put Rømer 's observations in Paris continuing. The benefits are not only systematic deviations confirmed but it strengthened the presumption that the eclipses - in comparison to the prediction - formerly occurred when the earth is at its annual orbit around the sun (A) Jupiter (B ) on the arc of D to H approaches opposition position on F and G (see right drawing of Rømer ), and later as the schedule predicted, when the Earth from Jupiter from H to L and K to e Konjunktionsstellung. The reason for this is that the light path between Jupiter and Earth changes, and thus - because if the speed of light is a finite size - even the light travel time. Rømer ventured on August 23, 1676 prediction that the eclipse of the moon Io (DC) " too late " will be visible on November 9, 1676 by ​​ten minutes. As this delay actually entered, he turned his explanation of the Royal Academy of Sciences ( Académie des Sciences ) in Paris on November 21, 1676 and published before it on December 7, 1676 in the Journal of sçavans under the title " le mouvement de la Démonstration touchant lumière trouvé par M. Roemer de l' Académie des sciences ".

In this article, but not the speed of light, but only the time will be required for the light to traverse the diameter of Earth's orbit. According to Romer's bill, the value was about 22 minutes; the correct value is 17 minutes. For Rømer, it was important to show that the light propagates not instantaneous, but with a finite velocity. Rømer was only an upper estimate of the speed of light: for the diameter of the Earth need the light less than a second, according to current knowledge, there are only 0.0425 s

Romer's interpretation was soon accepted by Isaac Newton, John Flamsteed, Edmond Halley and Christiaan Huygens. Cassini and many others have followed long will the view of Descartes, that light propagates instantaneously. In general, the finite speed of light was recognized only after James Bradley's discovery of the aberration of light in 1729.

A value for the speed of light was s calculated for the first time in 1678 by Christiaan Huygens with about 212,000 km / in today's units. He used the term specification of 22 minutes (= 1320 s ) of Rømer. For half the diameter of Earth's orbit ( Astronomical Unit ) he sat 11,000 a diameter of Earth, so for all the Earth's orbit diameter is about 280 million km in today's units. He was based on a specification of the solar parallax of 9.5 arcseconds, which had received Cassini in 1673 from a Mars observation ( from C. Huygens Treatise of Light, did not appear until 1690). Rømer has this figures certainly had access, but it is not used.

To date, numerous astronomical and physical professionals and textbooks historically false readings and disabled measuring situations are informed about Jupiter conjunct (that day) and in opposition (no shadows visible). Historian of science tried in vain so far, the facts rectify (see literature).