Telescopes dew up at night and heaters on the optics stop it, and the heaters are on a controller that logs the current to each one. The controller logs a heater that is not connected. It is the channel that ran the finder scope, a small telescope bolted to the big one for aiming, which was removed when the computer pointing came in. The channel draws current every night. The bolt holes where the finder was are warm to the touch and dry, on a tube that is running with dew.
I am the telescope operator at an observatory and the dew heater controller is the least interesting box in the dome, and it has one channel that is not mine.
The heaters.
Strips round the optics, warmed a degree or two above the air so the dew forms somewhere else, on a controller with six channels that logs the current on each. Five are connected. The sixth, channel four, was the finder scope, a small refractor on the side of the main tube that the observer looked through to aim, and the finder came off in 1990 when the pointing went computerised, and the channel was left, and has nothing on it.
Channel four draws current.
The current.
About an amp. Every night, from when the dome opens to when it closes. The controller shows it. The cable for channel four ends in a plug hanging off the side of the tube, connected to nothing, and I have had a meter on the plug and there is current going into nothing.
And the place on the tube where the finder was, which is four bolt holes and a ring of less faded paint, is warm. On a night when the main tube is running with dew, when the dew is dripping off the mount, the ring where the finder was is dry, and warm, a degree or two above the air, exactly what a dew heater does.
There is a finder scope there. It is being kept clear. I cannot see it.
What has been checked.
The controller, replaced. Channel four draws an amp.
The tube, at midnight, by me, with my hand in the ring. Warm. Dry. And above the ring, where the finder's eyepiece would have been, at the height of the observer's eye when the telescope is at that elevation, the air was warmer still, in a small space, the size of a face, and the dew on the tube beside it had a clear patch, and I put my own face into the space, where the eyepiece would be, and I looked, and there was the sky, through a finder that was not there, a wide field with the crosshairs on it, the old illuminated kind, red, and a star on the crosshairs, and I stepped back and the tube was wet and the sky was the sky.
Who.
The pointing went computerised in 1990 and the finder came off, and the observer who had used the finder for thirty years, who had aimed the telescope by eye every night with a skill the records describe as, remarkable, had been told that the skill was no longer required, and had retired, and the observatory's history says he came back at night for a while, to sit in the dome, and that it had been awkward, and then he had stopped coming, and then he had died.
He is aiming. Every night. Through a finder that is not there, kept clear by a heater that is not connected, at stars the computer finds for us in a second, and it takes him longer, and he is better at it, and nobody has asked him to point at anything for thirty five years.
What is done about it.
Channel four is on the controller log every night at an amp and the power is paid for and the engineer has asked what is on channel four and I have said, the finder, and he has said there is no finder, and I have said, it's warm.
What I do.
I operate the telescope.
The computer points. It is very good. But there is a step in the night when the pointing is checked, where the operator looks through an eyepiece at a known star and confirms the telescope is where the computer says, and in 1990 that step was done through the finder, by him, and since 1990 it has been done by a camera, in a second, with nobody looking.
So I ask him. At the start of every night, when the dome is open and the first target is up, I say, to the ring of warm paint, to the space where the eyepiece was, can you check that for me, and I wait.
The computer's pointing log has a field for the check, which the camera fills in automatically with a number, the offset, how far off the telescope was. Since I started asking, the field has two entries each night. The camera's, and another, a second later, from a source the log calls, manual, which is a source that has not been used since 1990, and the manual offset is always smaller than the camera's, and the telescope, when I apply it, is dead on.
He is better than the camera. He always was. And I have started writing in the night report, in the section for instrument performance, that the pointing was checked manually and found to be excellent, and the director has asked me who is doing the manual checks, and I have said, the observer, and she has looked at the date on the report, and at me, and let it go.