Keeping an Observatory Logbook

Joachim Köppen Strasbourg 2008

The observatory's logbook serves two functions: to inform any user of the state of the instrument and whether there have been any problems or irregularities. If these were not recorded, it will be more difficult to identify the error and fix it. The other vital function is to keep all additional information about the observation itself, such as anything that is not recorded in the data file, but will or might be of importance for the interpretation.

What we should do:

• record the times of starting the system, and also when the system is closed down.
• every time you do something with the telescope or on the computer, write down the time and what you did. And better write down the numbers ...
  in the beginning the positional data were not recorded in the file and sometimes the exact position is important when interpreting the wiggles of the plot. Someone made a couple of failed attempts to observe the moon, and he had the impression that the positions did not agree with the predictions ... however, he did not keep any record at all, and thus the data he obtained are completely useless ... moreover, we could never find out what went wrong!
• record any irregularity of the system
• it is better to write down as much as possible: the measurements of the sun and the calibration source; although these will be stored in the file, it is good to write them down ... to see what values you get later in the observation period ...
• add your comments and explanations ... like "missed the sun again"; write down your impressions and thoughts ... even if you one hour later find out that you did something wrong or your interpretation wasn't correct ... you might have forgotten all that when you look at the data the next day! but then it is too late to exactly reconstruct what you had been doing!
• when you try out something or run a test, record what you do, why you do it, your thoughts and findings
• on 10 GHz the water vapour in the atmosphere causes absorption. While this may have only a small effect on strong sources (sun and satellites), it is crucial for a weak source, such as the moon. Thus it is a good point to look out of the window and record the weather ... this may make it later easier when you find that the measurements on one day are a bit different from the other days ...

• what you don't write down while it happens cannot be reconstructed in detail some time afterwards.
• paper (or a computer file) is patient: better write too much than too little.