Yes, Flying Electric Trousers. Years ago astronomers actually rode inside the Hale Telescope all night long. They would sit at the top end of the telescope in what is called Prime Focus. They would be up there to make sure the pointing and tracking were accurate, focus the camera, and physically pull the shutter to start exposing the image.
We have a nice look back at those from the late Jesse Greenstein. He gives two quotes that put things into perspective:
"Working at night in the small cage high above the primary mirror, feeling closer to the stars than the earth, remains an exhilarating and unforgettable experience."
"You also had to have a tough bladder because, if possible, if it was a good night, you stayed up from seven o'clock to five. That's ten hours!"
Imagine working high inside the telescope, by yourself, in the dark, for the entire night. Nights on Palomar can be cold, especially in the winter time. That's where the Flying Electric Trousers come into the story.
The trousers and shirt were used to keep the astronomers warm during the night. They were surplus F3-A electrically heated flying suits used by the U.S. Army Air Force during World War II.
Recently a cache of these old suits was uncovered at Palomar. One of the suits is now on display for the observatory's many visitors to see. If you are in the area, come and have a look. The suit on display belonged to Horace W. Babcock, Palomar's director from 1964 - 1978.
A few years ago Jean Mueller, telescope operator (aka Night Assistant) on the 200" managed to save one of the manuals for the old F3-A suits. It is fragile, but it has now been scanned. Here is the cover:
I can post all of the F3-A manual if people are interested in seeing it.
By the way, modern astronomers make use of the Hale Telescope from the comfort of a warm room. A large digital camera rides in Prime Focus. The room features computers for controlling the telescope & cameras, a stereo, coffee, a bathroom and heat. For our smaller telescopes the astronomers do not even need to come to Palomar. They can be operated remotely from the comfort of an office, kitchen or elsewhere.