Updating UTC/Earth rotation data
The rotation of the Earth is not constant. Events like earthquakes, volcanic eruptions etc. all add to tiny fluctuations in the Earth’s rotation. The 10Micron mounts correct for these fluctuations to ensure maximum pointing accuracy. For that purpose, the mount uses a public data-source, generated by NASA. This data is only valid for a certain amount of time and needs to be updated from time to time, approximately twice a year. Whether the average amateur astrophotographer will ever experience pointing or tracking issues by not updating it is highly questionable. But the mount and software that manages the mount, such as MountWizzard, give error messages if you don’t. So it is good practise to get rid of the error messages by updating this data when expired. The updating process is extremely simple, but not very intuitive. Therefore in this blog the few simple steps to follow.
Step 1: Download the data
The data that is required consists of the following two files: tai-utc.dat and finals.data. The first one is a small table with corrections for discrepancies between the International Atomic Time (TAI) and the Coordinated Universal Time (UTC). Both tend to diverge over time and to bring them together again, so-called leap-seconds are used. Currently 1 leap-second is added every 2-3 years. So this file doesn’t change much over time. The finals.data file contains the Earth Orientation Parameters (EOP), which describe small irregularities in the earth’s rotation, based on actual observations. The EOP are produced by International Earth Rotation Services (IERS) and updated weekly. The latest finals.data file (IAU1980) can be found here: https://www.iers.org/IERS/EN/DataProducts/EarthOrientationData/eop.html. The tai-etc.dat file only changes ones every couple of years.
It is easiest to get the latest version of both files from a mirror and/or archive server. This used to be a US Naval Observatory (USNO) server (Maia.usno.navy.mil/ser7), which is also mentioned in the 10Micron software. However, this server has been taken out for maintenance and has not come back up again yet. Currently the best place to find both files is https://cddis.nasa.gov/archive/products/iers. Until October 31, 2020 this was a freely accessible server. But for access after that data, you have to register for a (free) account at NASA CDDIS. Once logged in, you will see a long list of files, in which you should look for tai-utc.dat and finals.data.
Step 2: Connect to the mount
To load the data-files into the mount controller, you need the 10Micron Updater Software that comes with the mount. Upon starting the software it searches for a connection to the mount. 10Micron recommends a wired connection using Ethernet, but I always use the mount through its WiFi connection and never had a problem.
Next there will be a pop-up screen where you can choose what you want to update. Un-tick all boxes, except the bottom one that says UTC/Earth rotation data. As a side-note, this is also the place where you can load the latest comet-data, so that you can point the mount with the hand-controller to a newly discovered comet.
Next you click on ‘Edit…’
Step 3: Import the data into the mount
Now comes the counterintuitive part. In the pop-up screen you will see that the software is asking for the tai-utc.dat and finals.data files. But when you click on ‘Import files…’, make sure you load the finals.data file first. Once you’ve done that, the system will ask for the tai-utc.dat file.
After that, you will be guided through the next steps and the data will be loaded into the mount. This should be done in a matter of seconds.
Once you have completed the process, the error-messages will be gone. In MountWizzard you can always check what the expiration date is for the loaded Earth rotation data, so you can prepare in time for the next round.
Update 05 February 2023
In recent versions of the firmware update tool there are a few subtle but relevant changes:
The software now asks for the finals.data file first, which is the right order. So the process is still the same, but the software is now clear about that too.
The software now asks for a CDFLeapsecondstable.txt file instead of the tai-utc.dat file. These are essentially the same. In fact if you open the txt file, it mentions that the data is from the tai-utc.dat file. The mount will accept either file. By the way, this file almost never changes. The last leap second has been added in 2017.