Thursday, December 10, 2015

Past to the Present

A joint Belles blog post! On November 18, 2015 we had an observing field trip to Mount Wilson Observatory - the place where Carnegie Astronomy began.

We owe so much to the astronomers, scientists, engineers and telescopes that came before us. Luckily  in the case of Carnegie, the original telescopes have been preserved and lovingly maintained by the Mount Wilson Institute on a mountain just above Pasadena.

Mount Wilson Observatory Carnegie Science 60-inch telescope
Four Las Campanas Belles were Mount Wilson Belles for the night. L-R: Erika Carlson, Rachael Beaton, Johanna Teske, Cynthia Hunt stand in front of the 60-inch reflector and the starry night sky.

Originally called the Mount Wilson Solar Observatory, the first permanent telescope on the mountain was the Hale Solar telescope in 1904. Named after Helen Snow who donated the coelostat, this horizontally projected telescope was the predecessor to the 60-foot solar tower and 150-foot solar tower.

Looking up the 150-foot solar telescope.
Photo by Paul Collison.
The Solar disc at the focus of the solar telescope, with the
largest sunspot group ever recorded, and marbles the size
of Jupiter and the Earth to scale.
Photo by Erika Carlson
We arrived at Mount Wilson in time to watch the sun set in a most unusual way: at the focus of the 150-foot solar telescope. Operator Steve Padilla kept the coelostat aimed at the sun as it dipped below the horizon of the Pacific ocean. When the sun started to turn orange, Padilla placed a to-scale image of the largest sunspot ever recorded in 1947, with a large marble the size of Jupiter and a small bb that is the size of the sun. At sunset, the atmospheric refraction and the reflection off the pacific ocean caused wonderfully deep red ripples, occasionally cut through by the silhouette of an airplane landing at LAX.

George Ellery Hale already had visions of the world's largest telescope, long before Mount Wilson Observatory was conceived, and even before the 40-inch refractor came online at Yerkes Observatory. With backing from his father, he commissioned the glass blank for the 60-inch mirror in 1894, and only accepted the directorship at Yerkes with the condition that they build a telescope with his mirror.  The University of Chicago failed to find funding for the telescope and mount for Hale's mirror, so he ended up donating the partially ground mirror to the recently formed Carnegie Institution of Washington in 1905 after moving to Pasadena. After years of tedious grinding and polishing the mirror's surface (so it was perfect within a few millionths of an inch!), constructing a totally new and very large mount and movement system for the mirror, surviving the 1906 San Francisco earthquake and widening the existing road up the mountain, the 60-inch mirror had it's first light on December 13, 1908 and the first exposures were recorded soon after (see below). It remained the world's largest telescope until the Mt. Wilson 100-inch was completed in 1918.

Orion Nebula. First light on the 60-inch telescope - December 24, 1908.
Image courtesy Carnegie Observatories Plate Archive and Dan Kohne.

The 60-inch telescope is, according to Dr. Allan Sandage, "the grandaddy of them all, where many of the problems of telescope design and solutions were first understood." The size of the telescope made it possible to obtain useful spectra of fainter nebulae and stars than ever before, leading to the discovery that the Andromeda Nebula (as it was known at the time) had a spectrum resembling the Sun's. Hale deduced from this that it was also full of stars; the 60-inch also provided the first photographs of stars in other galaxies.

The Mt. Wilson 60-inch also played a crucial role in advancing the research of one of our favorite Belles of the past, Henrietta Swan Leavitt. She was the first to recognize the importance of Cepheid variable stars, giant stars that brighten and fade on a time scale that is directly related to their true brightness (longer the period of variation, the brighter the star). Ms. Leavitt's period-luminosity relation made Cepheids the first "standard candle" in astronomy, making it possible to determine distances to far-away galaxies. Dr. Harlow Shapley of Mt. Wilson Observatory used Ms. Leavitt's period-luminosity relation to measure the distances to hundred of globular clusters (that he thought were) in the Milky Way, finding that the most distant clusters are about 200,000 light years away! This led to the Great Debate (the Shapley-Curtis Debate) at the Smithsonian Museum of Natural History, in which Harlow Shapley and Heber Curtis argued over the size and nature of the universe. The work of Edwin Hubble at the 100-inch on Mt. Wilson ultimately proved that the Milky Way is only one of hundreds of billions of galaxies in the observable universe. All of this was made possible by Ms. Leavitt, and by the facilities at Mt. Wilson Observatory.

Carnegie Science VAR Hubble plate Observatories
Image of the glass side of Hubble's H335H photographic plate of the Andromeda Galaxy, taken at the 100-inch on the night of Oct. 5-6, 1923.  The letters "N" mark novae, and the first Cepheid variable discovered in Andromeda has its letter "N" crossed out and is relabeled by Hubble as "VAR!" for variable. This discovery helped establish that Andromeda was a separate galaxy from our own.
Image courtesy of the Carnegie Observatories

Thus it was our great privilege to get to participate in eyepiece observing at the 60-inch for several hours. We got great views of the Moon (craters look really different up close!), Uranus, Neptune and Triton, globular clusters, open clusters, and planetary nebulae. This was the opening night for Dr. Chris Burns, a Carnegie research associate, who has been training to be a 60-inch operator for months. He gave us an exciting but smooth tour of the night sky above Los Angeles, which we all forgot was only a few miles away. You can see what I mean here.

It's worth checking out the photo reels from two staff members who captured our trip from the whole afternoon and evening: the Observatories IT/IS Manager Paul Collison's photos are here, and Observatories Facilities Manager Scott Rubel's pictures are here.

Many thanks to the Mount Wilson Institute and the Carnegie Observatories for giving us the opportunity to step into the shoes of the giants of astronomy for the night!

Mount Wilson Observatory observing 60-inch Carnegie Science
Erika observing through the eyepiece of the 60-inch telescope.
Photo by Paul Collison

The 60-inch telescope during our evening session: eye on the sky since 1908.
Photo by Cynthia Hunt


  1. Yeah, great post, Cynthia! Makes me miss Mt. Wilson even more!