who was the first to attempt to measure it?
"Isaac Beeckman", in 1629.
Speed of light
In 1629, Isaac Beeckman proposed an experiment in which a person observes the flash of a cannon reflecting off a mirror about one mile (1.6 km) away.
what is the value of speed of light in vaccum Its exact value is defined as “approximately”, because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of second.
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Speed of light [SEP] First measurement attempts
In his 1704 book "Opticks", Isaac Newton reported Rømer's calculations of the finite speed of light and gave a value of "seven or eight minutes" for the time taken for light to travel from the Sun to the Earth (the modern value is 8 minutes 19 seconds). Newton queried whether Rømer's eclipse shadows were coloured; hearing that they were not, he concluded the different colours travelled at the same speed. In 1729, James Bradley discovered stellar aberration. From this effect he determined that light must travel times faster than the Earth in its orbit (the modern figure is times faster) or, equivalently, that it would take light 8 minutes 12 seconds to travel from the Sun to the Earth.