Geared to the Stars

The telescope at Ladd Observatory uses a clock drive to compensate for the Earth's rotation and track the stars. Modern telescopes use electric motors but this one was built in 1891 before electric power distribution was common. The Observatory originally had gas lamps for lighting and the telegraph system was powered by "gravity cell" batteries. The telescope's mechanical clock drive is weight driven with the speed regulated by a centrifugal friction governor.

A closeup of the clock drive showing the governor in motion.
An optical sensor and precision timer are used to measure the rotation rate.

Prismatic Analysis

One of the projects that I've been working on is the Brashear astronomical spectroscope from 1891. We're trying to recreate the ability to record spectra using the original photographic plate holder. Here is the wooden plate holder mounted in place of the eyepiece assembly that is used for visual spectroscopy.

A focusing screen was created by mounting the ground glass in a foamcore frame that fits the plate holder.

The Transits of Venus

The 2012 transit of Venus by Michael Umbricht

The June 5, 2012 transit of Venus across the Sun at 6:21:38 PM EDT captured using a modern digital camera through the historic main telescope at Ladd Observatory.

The telescope is a refractor with 12" aperture and 15' focal length. A solar pre-filter was used on the objective of the telescope and the camera used a broadband hydrogen alpha nebular filter to further reduce the brightness due to the sensitivity of the camera. The weather was mostly cloudy during the day and this image was taken during a brief thinning of the clouds which gives the Sun's surface a mottled appearance. 

The photo at left shows Michael Umbricht preparing the telescope and camera before the transit.