06 Jul Discovering Mount Wilson Chapter 4: 60-foot Solar Tower Telescope
We continue “Discovering Mount Wilson” with Chapter four, highlighting the 60-foot Solar Tower Telescope. George Ellery Hale knew he needed something to correct the distorted images caused by the sun heating the ground when using the Snow Solar Telescope. His solution? Build a telescope with “a high tower and no tube.” This worked by placing mirrors and a lens high above the heated ground, which would avoid many of the problems encountered by the Snow Solar Telescope. This enabled astronomers to use a large spectrograph in a pit beneath the tower where the temperature would remain almost constant.
The 60-foot Tower was completed in 1908, becoming the world’s greatest tool for solar research. Its vertical tower design allowed much higher resolution of the solar image and spectrum than the Snow telescope alone could achieve.
On June 25, 1908, with the new telescope in place, Hale achieved one of his greatest astronomical discoveries: he detected for the first time that magnetic fields exist outside of Earth. Hale observed spectral lines that were split into two or more lines, within the spectrum of a sunspot, which indicated the presence of a magnetic field. This splitting of spectral lines, known as the Zeeman effect, was discovered in laboratory experiments by Dutch physicist Pieter Zeeman (1865-1943) in 1896, for which he received the 1902 Nobel Prize in Physics.
The success of the 60-foot Solar Tower Telescope – at the time, the world’s largest — prompted Hale to begin work on his next achievement, the 150-foot Tower.
Hale’s solar work in the early days of Mount Wilson was of such great importance that it became the foundation for almost all solar and stellar research to follow.