I am pleased to introduce this series of articles from John Perlin, based on his ground breaking book, “Let It Shine: The 6,000-Year Story of Solar Energy.” Perlin will discuss the major breakthroughs in solar energy over the millennia.
First Major Breakthrough – Learning where the sun is throughout the year
No one seems to know where the sun is these days. Ask just about anyone and they’ll say it rises in the east and sets in the west the year round. That’s is as exact as they get. Thousands of years ago, the ancient he Chinese, though, knew precisely where the sun would be in relation to the earth, minute by minute, day after day, season to season. They were able to compile such data through their invention and use of the gnomon, a simple but precise instrument that consisted of a stick placed at right angles to the ground. As the sun moved across the sky, they recorded the changing length of the shadow of the sun cast by the gnomon (nomon).
The great philosopher of science Thomas Kuhn credits the gnomon for systemizing and quantifying “a vast amount of common but vague knowledge about the daily and annual variation of the sun’s position and in the process, using the sun as “a time reckoner and calendar keeper.”
The gnomon became a time keeper since its shadow grows larger throughout the day. It became a calendar keeper by its changing shadow throughout the year.
The long shadow cast by the gnomon in winter confirmed observations that at this time of the year, the sun remains low in the sky throughout the day. That the shadow’s stays put in the north throughout the day verified an observation made by an ancient Chinese astronomer: “On the day of the winter solstice, one does not see the sun in the east or west.”
Just the opposite occurs at the summer solstice. During mid-afternoon, the Chinese recorded the shortest annual shadow for the shortest time in the north indicating that the sun was at its highest point for the year and spending the least amount of the day in the south. They also found that the shadow fluctuated dramatically – toward the west during the early hours of the morning and toward the east in the late afternoon.
These solar facts substantiated by the gnomon lead to a second major solar breakthrough initiated by the Chinese – building with the sun in mind to use its rays for winter heating while avoiding them in summer to keep cool – which will be covered in the next installment of this series showing how solar techniques evolved, bettering the lives of millions.
“The Five Major Breakthroughs in Solar Energy” will be followed by four additional installments:
- Breakthrough Number 2 – Building with the Sun
- Breakthrough Number 3 – Trapping Solar Heat with Clear Materials
- Breakthrough Number 4 – Concentrating Solar Energy
- Breakthrough Number 5 – Photovoltaics – The Direct Conversion of Light
- into Electricity
Source | Images: “Let it Shine”, by John Perlin.
John Perlin is author of four books: “A Golden Thread: 2500 Years of Solar Architecture and Technology;” “A Forest Journey: Wood and Civilization;” “From Space to Earth: The Story of Solar Electricity;” and his latest book, “Let It Shine: The 6000-Year Story of Solar Energy.” Harvard University Press Chose “A Forest Journey” as one of its “One-Hundred Great Books” published by the press, as well as a “Classic in Science and World History.”