Ole Romer

Ole Christensen Rømer (September 25, 1644, Århus – September 19, 1710, Copenhagen) was a Danish astronomer, famous for being the first person to determine the speed of light in the year 1676 with an initial value of 225,000 km/s. He was, in turn, the inventor of the micrometer to observe eclipses and the meridian telescope (meridian telescope). In 1701, Ole devised a temperature measurement scale called the Rømer Degree, which has now fallen out of use.

Biography

Rømer was born on 25 September 1644 in Aarhus, the son of merchant and patron Christen Pedersen (died 1663), and Anna Olufsdatter Storm (c. 1610 - 1690), daughter of a well-to-do alderman. From 1642, Christen Pedersen began using the name Rømer, meaning he was from the Danish island of Rømø, to distinguish himself from other people named Christen Pedersen. There are few records of Ole Rømer before 1662, when he graduated from the old Aarhus Katedralskole (Aarhus Cathedral School), moved to Copenhagen and enrolled at the University of Copenhagen. His mentor at the University was Rasmus Bartholin, who published his discovery of the double refraction of a ray of light by the Icelandic spark (calcite) in 1668, while Rømer was living in his house. Rømer had every opportunity to learn mathematics and astronomy from Tycho Brahe's astronomical observations, as Bartholin had taken it upon himself to prepare them for publication.

In 1672, thanks to the intervention of Jean Picard, he went to France, entering the recently created Academy of Sciences in Paris. This academy was created in 1666 during the reign of Louis XIV.

His minister Colbert realized the importance of France becoming the leading scientific power and, with seemingly unlimited funds, got Christian Huygens, Picard and, above all, Giovanni Doménico Cassini to join the project.

Through the influence of Rømer, the Gregorian calendar was introduced in Denmark in 1701.

On September 19, 1710, at the age of sixty-five, Rømer died as a result of a stone.

Almost all of the illustrious astronomer's manuscripts were lost in the terrible fire that destroyed the Copenhagen Observatory on October 20, 1728.

His work

Measuring the speed of light with Jupiter's satellites

Ole Rømer using its telescope

The observations of Jupiter's first satellite made by Römer and Giovanni Doménico Cassini indicated an inequality, which the two scientists believed they could attribute to the successive propagation of light (Paris Observatory, year 1676). Cassini wasted no time in discarding such a just idea; On the contrary, Römer kept it, thus linking his name to one of the greatest discoveries that modern astronomy is proud of.

One night in 1676, Römer was observing Jupiter's moons by himself and realized that the time span between Jupiter's eclipses with its moons was shorter when the Earth was moving toward Jupiter, and longer when she was walking away. With his telescope, he carefully observed Jupiter's satellite Io and estimated that it took light 22 minutes to cross the diameter of Earth's orbit, although modern estimates are closer to 17 minutes.

It has been noted that after the very happy idea of attributing the differences observed between the turns of Jupiter's first satellite to the limits of the shadow cone during the first and second square of the planet and to the propagation of light, Römer, inexplicably, disdained to demonstrate that in the same hypothesis was the explanation of the inequalities noted also in the other three satellites.

It might be surprising that you haven't tried to estimate the speed of light more accurately than you applied. Horrebow, Römer's favorite disciple and his most ardent admirer, sets the time it takes light to travel the distance from the Sun to Earth at 14 m 10 s instead of 8 m 13 s.

The telescope

Römer, who had witnessed in Paris the difficulties in making the lens of a wall quarter-circle move in the plane of the meridian, that is, a lens balanced on a very short axis and forced to apply continuously on a limb imperfectly made, he imagined and built the meridian telescope.

This instrument, which today can be seen in many astronomical observatories, is therefore due to the inventiveness of the Danish astronomer.

The Micrometer

He is also responsible for the invention of an ingenious micrometer, very commonly used towards the end of the 17th century to observe eclipses. With this micrometer it was possible to increase or decrease the image of the Sun or the Moon until they were between two threads located near the eyepiece.

From the properties of the epicycloids he deduced the most suitable shape that the teeth of a cogwheel should have to ensure a uniform movement.

Eponymy

• The Ole Rømer Observatory of Aarhus in Denmark.
• The moon crater Römer.
• The asteroid (2897) Ole Römer.