Occult v4.2022.x.x

Occultation Prediction Software
by David Herald


  1. What is Occult v4.2022.x.x
  2. First Time Installation Instructions and Notes
  3. Updating Occult
  4. Copyright Issues


Occult is designed to generate occultation predictions, and analyse occultation observations, for a wide range of occultation phenomena, including:

In making these calculations, Occult uses many basic astronomical calculations. Many of these are made available for general use, such as:

To make these calculations, Occult provides for downloads of 42 separate data files which are subject to regular revisions. In addition Occult can use a number of star catalogues having file sizes of several GB (for example, a downloadable subset of the Gaia EDR3 catalogue to mag 16.0, file size 2.64GB, and UCAC4 with a size of 8.6GB [which needs to be separately obtained]).

The program is regularly updated, with a full list of the program changes being provided in Occult under the menu item Program updates - List version changes


You need to download and save (use right click on your mouse and select "Save target as"):

To install Occult:

Now run Occult. Occult will complete the installation by creating a number of subdirectories, downloading the two data files (unless you have already downloaded them and placed them in the Occult directory), and unzip them into the relevant directories. Occult will then take you to a page that displays a range of default settings. You can change the settings here at any time after Occult has been installed. However at this stage you should do the following:

You will then be taken to the download page, where you can download the latest versions of a number of data files - including some large catalog files. The files that need to be downloaded will be tagged with a chevron. However you do not need to download them immediately.

Finally you will be taken to the main form of Occult, where you can use its functionality.

To assist you in learning how to use the program, the Help file system includes a topic First time user - examples. You should work through each of the examples under this topic - to become familiar with how the program works, and the functions that are available. [If you can't access the Help topics, click the menu item Help... if Help not working on the main form of Occult for instructions on how to fix the problem]


When you run Occult, the existence of updates will appear at the bottom-left of the main form. To update, simply click the update text. The frequency at which Occult will check for updates is set in the User Settings, which are accessed from the Maintenance tab of Occult. You can manually check for updates using the Menu item Program updates...

If for some reason you need to do a manual update of the program files:

Tips for using Occult by David Dunham (pdf file)


Occult relies heavily on data that is freely available. Items such as various star catalogues and the planetary ephemerides have been developed by government funded agencies or grants. Occultation and graze observations have been contributed mainly by the efforts of amateur astronomers (or as I prefer to call them, unpaid astronomers) from around the world. This contribution needs to be recognized and acknowledged.

The philosophy behind my writing and maintaining Occult is to encourage useful observations of occultation phenomena, thereby increasing our knowledge of the world around us. Accordingly:

For the record, I reserve all rights to the Source code and any decompilation thereof - but with IOTA being able to continue to maintain/improve the program on the same basis as above, when I am no longer in a position to do so.

Dave Herald
October 2022


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