Solar Energy Research

The foundations of solar energy and climate research were laid at the Allegheny Observatory in the late 1800s. While most astronomers were studying the positions of stars and planets in the sky, Samuel Langley wanted to know what the stars, and particularly the sun, were made of. Langley began studying the nature of the light and heat coming from the sun. Langley mapped the intensity of the sun's heat energy reaching the earth using spectroscopy. He carefully measured the intensity of heat energy, or infrared light, along its wide spectrum of wavelengths. He also made the same measurements on top of California's Mount Whitney, which is over 14,000 feet high. Most of the earth's atmosphere lies below that altitude, and so the air is much thinner there. Langley compared the differences between the sun's energy that reaches the earth closer to sea level with that on the mountain top. He learned that specific wavelengths of the sun's heat energy are being absorbed by water vapor in the air. As we now know, absorption of the sun's energy by gases in the earth's atmosphere influences the world's climates.

• Langley's assistant, James Keeler, performed similar experiments and later learned that certain wavelengths of the sun's energy are also absorbed by carbon dioxide in the air. As is the case for Langley's discovery of absorption of the sun's energy by water vapor in the atmosphere, this knowledge formed the foundation for today's climate research.
• Langley was such an important pioneer in the study of the sun's energy that the unit of solar energy distribution over an area, the langley (Ly), was named in his honor.
• In 1906, when coal was plentiful and the oil industry was just beginning to prosper, John Brashear was perhaps the first person to recognize the limitations of fossil fuels and the potential benefits of solar energy. In an address to professors at Lehigh University, he said:
  

  Perhaps there will come a time when our fuel supply will be exhausted, then why not capture the original source of energy and make it do our bidding. Professor Langley calculated that it would require all the coal of all the coal fields of Pennsylvania to keep up the energy of the sun one thousandth of a second.
  
  When we learn that the solar energy, if conserved, would approximately equal a horse power for each square meter of the earth's surface for every twenty-four hours, we may surely consider it a problem worthy of profound study by our scientific investigators.