Nova computers

The Nova computer was a "16-bit minicomputer" introduced to McDonald Observatory around 1970 by Dr. Ed Nather for instrumentation control. In fact, Ed bought Nova SN 1 with drawings signed by Edson de Castro himself, the founder of the computer manufacturer, Data General Corporation. The machine was small enough to fit on a roll-around cart so that it could be easily used at the 30-inch or 36-inch telescope to control an instrument mounted to the back of the telescope.

Digital memory and micro-computers were not yet available, so the computer used core memory, up to 8 kilobytes per board (about 12" x by 12"), a CPU designed with small scale TTL digital "chips," and user-designed interfaces that all slid handily into the chassis. Software was loaded into the computer from paper tape using an ASR-33 teletype, and data in turn were punched to paper tape.

The light sensor was a photomultiplier tube, a one pixel device that converted photons to electronic pulses which could be counted by the Nova computer interface. In an effort to reduce internal noise, the tubes were kept cold in insulated boxes stuffed with dry ice. Condensation on the boxes during inclement weather would sometimes short out signal cables, so that at one time de-humidifiers were installed at the 30-inch and 36-inch telescopes.

Early on, Nova software was all written in "assembly language." High-level languages and operating systems came later. With an understanding of the Nova assembly language, software could be modified or entered using the computer front panel switches. Lights on the front panel permitted reading the software by stepping through the program one instruction at a time.

At night, the stillness in front of the TQ (Transient Quarters) was broken all night by the rat-a-tat-tat of teletypes punching UBV photometry data on miles of paper tape which was feed into a temporary storage receptacle — a trash can. And in the telescope, each tape punch was preceded by the mechanical sound of the filter wheel advancing about every second to the next color. Up until the Nova computer, the filter had to be turned by hand and the data written in a notebook.

The mini-computer revolutionized the measurement of flare stars, and put McDonald at the forefront of this branch of astronomy. But astronomy keeps moving on, so that now flare star photometry is relegated to amateurs and mini-computers are replaced by microprocessor chips.

The automated photometers freed the astronomer up to guide the telescope; this was before the day of automatic guiding. Astronomers on break would meet at the TQ for coffee with patches over their guiding eyes to maintain light sensitivity.