IOTA Title Image

Grazing Occultations 2018 - GRAZPREP Download

The GRAZPREP-software is a system to provide you with all necessary information about lunar grazing occultations as introduced by Eberhard Riedel in 2009. The old system of precalculated event prediction data files you could download in the past was replaced by the GRAZPREP software enabling any interested observer to create his/her own individual event predictions. Here you find some general information. Those not able or willing to run this software should give notice to IOTA/ES to still obtain predictions as files or in print.

Among all occultation phenomena in the sky grazing occultations of stars by the moon have a very unique character. The observation of these spectacular events does not require any large and expensive telescope, but rather a small and transportable instrument like many amateur astronomers own one. Here you can read a good overview about these events and their observations.

Introduction to GRAZPREP

GRAZPREP was designed as a tool to easily access the grazing occultation prediction data supplied each year to interested observers by IOTA/ES (see below). The software was tested under Windows 7, 8 and 10.

The main idea of the program is to easily visualize the complete list of all grazing occultation events in an area plus the complete line data for any selected event and (simultaneously on the same screen) both the geographic circumstances on earth and the enlarged topographic situation at the lunar limb including a fairly realistic display of the sunlit lunar portion as well as the approximate sky brightness due to the sun’s altitude. This way GRAZPREP assists in figuring out the best observing site in advance by graphically showing the expected apparent stellar path through the lunar limb terrain. A judgment about the entire graze circumstances is easily possible at a few glances and a selection of the best events quick and easy.

Besides that the software allows a filtering of the most suitable events according to a variety of personal preferences for individually selectable observing stations with any geographic center and radius. Also an output similar to the former GRAZEREG-output was included. Any graze line for any selected favorable offset to the predicted limit can be displayed in Google Earth. In addition a report form is included to enter and report occultation observations in a common IOTA-format.

Through the use of the LRO/LOLA topographic limb data the approximate number of dis- and reappearances is calculated for any site coordinates and elevation. GRAZPREP uses the high-resolution LUNLIMB-data provided by Dietmar Büttner, Chemnitz, calculated from the original LRO/LOLA source data.

The stellar positions are taken from the Gaia-Catalog (DR1) for over 90% of the stars.

A zipped installation file of the most recent version of GRAZPREP can be downloaded via

Unzipping and running this installation file installs GRAZPREP with all necessary data in a folder of your choice (do NOT install into the Windows Program folder offered as a default). The password required for the installation is "IOTA/ES". Also use the above site to download one of the prediction files matching your region.

After starting GRAPPREP first read the user's manual to become familiar with all the options of the software. The manual can be opened from the Main Menu under 'Open Manual for Help'! (this requires an installed Adobe PDF-Reader)