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The speed of light raises questions regarding the age of the universe, which are usually summed up under the term "[[starlight problem]]".

The speed of light raises questions regarding the age of the universe, which are usually summed up under the term "[[starlight problem]]".

==History==

==History==

In 1676{{#tag:ref|Some sources state 1675.<ref name="Moreux"/>|group=note}}, the Danish astronomer [[Ole Rømer]] became the first person who attempted to quantitatively estimate the speed of light. His method was based on observation of the orbit of the satellites of [[Jupiter]] such as [[Io]] and evaluating their [[eclipse]] data as seen from the Earth. The Dutch scientist [[Christiaan Huygens]]  was first who applied the arithmetic onto Rømer’s estimate for the maximum time delay between periodical observations of Io's eclipse by Jupiter at the Earth's nearest and farthest position with respect to Jupiter.<ref>{{cite web |editor=Steven Soter and Neil deGrasse Tyson|title=Cosmic Horizons: Astronomy At The Cutting Edge|publisher=New Press, American Museum of Natural History|year=2000|url=http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/p_roemer.html|accessdate=August 4, 2013}}</ref>

In 1676{{#tag:ref|Some sources state 1675.<ref name="Moreux"/>|group=note}}, the Danish astronomer [[Ole Rømer]] became the first person who attempted to quantitatively estimate the speed of light. His method was based on observation of the orbit of the satellites of [[Jupiter]] such as [[Io]] and evaluating their [[eclipse]] data as seen from the Earth. The Dutch scientist [[Christiaan Huygens]]  was first who applied the arithmetic onto Rømer's estimate for the maximum time delay between periodical observations of Io's eclipse by Jupiter at the Earth's nearest and farthest position with respect to Jupiter.<ref>{{cite web |editor=Steven Soter and Neil deGrasse Tyson|title=Cosmic Horizons: Astronomy At The Cutting Edge|publisher=New Press, American Museum of Natural History|year=2000|url=http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/p_roemer.html|accessdate=August 4, 2013}}</ref>

In 1849, the French physicist Fizeau developed method which enabled to measure the speed of light between two points at the Earth by means of using the light source, rotating strobe disc (spinning toothed wheel), and the mirror. He shone a light ray between the teeth of a rapidly rotating toothed wheel. A mirror reflected the beam back through the same gap between the teeth of the wheel over the round-trip distance of 17&nbsp;km. By varying the speed of the wheel, it was possible to determine at what speed the wheel was spinning too fast for the light to pass through the gap between the teeth, to the remote mirror, and then back through the same gap, and the rotational speed at which the light returned through the ''next'' gap. The experiment showed that the light traveled over the known distance in 1/18000 second. The resulting speed of light through air was obtained by dividing the known distance by time.   

In 1849, the French physicist Fizeau developed method which enabled to measure the speed of light between two points at the Earth by means of using the light source, rotating strobe disc (spinning toothed wheel), and the mirror. He shone a light ray between the teeth of a rapidly rotating toothed wheel. A mirror reflected the beam back through the same gap between the teeth of the wheel over the round-trip distance of 17&nbsp;km. By varying the speed of the wheel, it was possible to determine at what speed the wheel was spinning too fast for the light to pass through the gap between the teeth, to the remote mirror, and then back through the same gap, and the rotational speed at which the light returned through the ''next'' gap. The experiment showed that the light traveled over the known distance in 1/18000 second. The resulting speed of light through air was obtained by dividing the known distance by time.   

The more precise methods, involving a rapidly rotating mirror, have been used by Americans Michelson and Newcomb.<ref name="Moreux">{{cite book |author=Théophile Moreux|title=Pour comprendre la physique moderne|year=1948|url=https://books.google.com/books?id=CetIPAAACAAJ&dq=Th.Moreux+Pour+comprendre+la+physique+moderne&hl=sk&sa=X&ei=lvL9UcmvKcfY4QTvm4DwBA&redir_esc=y|language=French}}</ref>

The more precise methods, involving a rapidly rotating mirror, have been used by Americans Michelson and Newcomb.<ref name="Moreux">{{cite book |author=Théophile Moreux|title=Pour comprendre la physique moderne|year=1948|url=https://books.google.com/books?id=CetIPAAACAAJ&dq=Th.Moreux+Pour+comprendre+la+physique+moderne&hl=sk&sa=X&ei=lvL9UcmvKcfY4QTvm4DwBA&redir_esc=y|language=French}}</ref>