The Astrophysical Observatory is established in a wooden edifice built at the cost of the Smithsonian on the grounds south of the Smithsonian Institution Building. It is one of the earliest observatories to practice the "new astronomy," or astrophysics. SAO focuses its research on the study of solar radiation and the solar constant—the amount of energy from the sun that strikes the outer edge of the earth's atmosphere. More - http://siarchives.si.edu/collections/siris_sic_566.