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Harquahala Peak Observatory

It was in the late 1800’s when  Dr. Samuel

Peirpont Langley proposed that the sun caused

 changes in the climate of the earth. He believed

 that by measuring these, the solar constant, he

and other scientists could accurately predict the

weather. Dr. Charles G. Abbot, Dr. Langley’s protégé,

 began to pursue his theory, and began testing at the

Harquahala Mountain Observatory. Telescopes were

not used here. Instead they used a variety of

 instruments. A coelostat was used to first reflect

sunbeams into the observing chamber. Next, a theodolite

was used to measure the altitude of the sun above the

horizon. Then a pyranometer was used to measure the

heat from the atmosphere around the sun. Finally, two

pyrheliometers measured the heat from the direct and

scattered rays from the sun. Readings of these

instruments, were recorded onto other instruments.

Then, scientists calculated the data by hand, and sent

the reports to the Smithsonian Institution of Washington D.C. This data was compared with recordings from other observatories from around the world. Eight scientists from 1920-1925 were sent from the Smithsonian Astrophysical Observatory were sent from Washington D.C. However, in 1925, it was decided that the severe weather, increased haziness in the air, and difficult access caused the station to be moved to Table Mountain in southern California.


The building that stands today was the observatory which included the laboratory and living quarters on each floor. In December of 1920, tie rods were added to the structures to fix the cracks that developed. One year later, corrugated iron was added to protect the fragile adobe walls. Between 1921-1922, cisterns, porches and a workshop were built. These structures have collapsed and in 1975, the site was added to the National Register of Historic Places.

Communication at first was by heliograph, or reflecting Morse code signals on mirrors. However, this took a lot of time and night and cloudy times caused problems. Next up was wireless radio’s transmitted to the nearby Wenden. However, the tall towers were hard to keep upright on the windy summit. When this method was abandoned, they were used as receivers to listen to national broadcasts. Finally, the telephone was the answer to the communication problem but needed lots of wire to be ran up the rough trail. Communications on the mountain today include microwave facilities used to direct the water flow in the Central Arizona Project.




"Harquahala Observatory." Arizona Pioneer & Cemetery Research Project. N.p., n.d. Web. 21 Mar 2010. <>.