Guest post by Liesbeth Venema, Senior Physics Editor, Nature
We are basking in light. In our daily lives we encounter a multitude of light-based technologies from basic lighting, optical fibre communication, television and computer screens, to diagnostic techniques in healthcare. Sunlight energy harvesting will almost certainly be essential to match the world’s growing energy needs. The International Year of Light 2015, which is celebrating these achievements, and more, is now in full swing.
Of course, light plays a key role in scientific inquiry and discovery. To take a closer look, we have opened up a poll to find out what are the most striking, beautiful experiments with light. To have your say, please click here and simply select three experiments from the list of candidates that would be top of your list. Over the next few weeks, we will introduce the candidate experiments on this blog, in chronological order. The results of the poll will be announced here at the beginning of May.
So let us start – with Greek philosophers who of course already pondered the nature of light. They debated for example how we can see: with light emitted by our own eyes or by absorbing rays that reflect from objects?But the first experiment on our list is a down-to-earth measurement, literally, using shadows and trigonometry to calculate Earth’s circumference. Circa 240 BC, the mathematician Eratosthenes determined the sun’s altitude in Alexandria at noon on midsummer’s day, from the shadow of a tower. Knowing also the distance to Syene in Southern Egypt, where the sun would be straight above at the same time, he worked out the circumference of the earth (around 40.000 km), within an error of at most 16%.
By the middle ages, the centre of scientific progress had shifted to the Arabic world. A highlight is the appearance around 1015 of a seven-volume work on optics by the Iraqi-born scholar Ibn Al-Haytham. The 1000th anniversary of this treatise is one of the highlights of the International Year of Light.
Nevertheless, our next experiment is attributed to Ibn Sahl, another Arab scholar, who in 984 discovered one of the most fundamental properties of light: refraction. Knowledge of the law of refraction, now better known as Snell’s law, enables the design of mirrors and lenses, which play a pivotal role in the discovery of microscopic as well as astronomical worlds – as we will find out in next week’s instalment.
Experiments covered this week:
240 BC Eratosthenes’ calculation of the earth’s circumference using a tower’s shadow
984 Ibn Sahl’s discovery of the law of refraction
In the next blog, Iulia Georgescu looks at Huygen’s observation of Saturn’s rings by telescope and Newton’s prism, splitting the rainbow, among others.