During my recent vacation in California, I visited Griffith Observatory. It is one of the most impressive landmarks in Los Angeles, built on top of a mountain in Griffith Park, North of Hollywood and right next to the famous Hollywood sign.
This observatory hosts a 12-inch refracting telescope and is open for viewing by the general public since 1935. It is named after Griffith J. Griffith, who ordered the construction of a public telescope after looking through the 60-inch reflector telescope at Mount Wilson Observatory in 1910. He was deeply moved by the experience, and wanted to offer the general public a similar view the of the celestial wonders.
It is neither the largest nor the oldest telescope in the world, but more people have looked through this telescope than through any other telescope in the world. Each new visitor that looks through the eyepiece will actually set a new world record! (And they then loose that record after about 30 seconds, when the next person starts looking through the eyepiece.)
During my visit in April 2018, over 8 million people have observed the Moon, planets or other bright objects through this telescope. The telescope is open for viewing on every clear night except Mondays, and visits are always free of charge.
The telescope itself was built by Carl Zeiss in 1931, and completed in 1935. It is mounted on a stress-compensated equatorial fork mount, which means that the tube itself is kept straight mechanically and does not bend under its own weight.
The main telescope is a 12-inch, f/16.7 refractor (5000 mm focal length). Two additional telescopes are mounted piggyback on top of the 12-inch Zeiss: a 9½-inch refractor (acquired in 1955) and a 9¼” Celestron SCT (from 2006), which provides live images using a digital camera.
Since Earth rotates, the telescope tube also needs to rotate slowly in the opposite direction to keep objects centered in the field of view. A small electric motor (1/70th Horsepower, ~11 watts) rotates the 4.5 ton assembly exactly once every 24 hours, and since this telescope was built before the invention of computers, the precise rate of rotation is controlled with analog electronics. Griffith Trust paid around $15,000 for this instrument in 1931, which is the equivalent of about $230,000 in 2018.
Due to its popularity, the waiting line for the 12-inch refractor is usually 30-40 minutes. Since 2003, there are also several (modern) mobile telescopes setup on the lawn outside of the observatory, which usually have much shorter waiting lines.
I was able to observe the planet Venus through both a computerized Celestron NexStar 11” SCT telescope, and the 12-inch refractor. The image quality of the modern instrument was much better, despite it being much smaller and lighter. It’s amazing how the capabilities of optical equipment have progressed in 80 years.
During the day, you can also view the sun through the coelostat, a device that tracks the movement of the sun. It provides 3 different views of the sun: a projected white-light sun image, the solar disk in hydrogen-alpha (spectrohelioscope), and the complete visible spectrum of our sun with dark Fraunhofer absoption lines (spectroscope).
The observatory also has several exhibits on the ground floor. One of these exhibits features two Schmidt plates from the 1950’s, photographed through a 48-inch Schmidt telescope for the Palomar Observatory Sky Survey. Surprisingly, I recognized something on one of these plates: Markarian’s Chain of galaxies in the constellation Virgo!
Another part of the exhibition displays a research line, large format cooled CCD camera manufactured by SBIG in the early 2000’s. This is a serious piece of astrophotography equipment!
At the end of my visit, I could enjoy a beautiful view of the city under a bright full Moon. It’s really hard to capture all the details and atmosphere on camera, especially with an old cellphone, but definitely worth the trip!
Astro Virus 
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