Crescent observation trainer

Version of 27.03.2008, Martin Elsässer


I have written a small visual tool, to practise seeing / finding faint lunar crescents. These are often of very low contrast, compared to the surrounding sky. As with most things, practice and preparation can make things easier.
The tool allows to set the elongation and orientation of the crescent, the brightness and colour of the sky, the brightness gradient of the sky, the field of view and the color and brightness of the crescent.

Required environment

The programm requires a Java 5 runtime environment (JRE), which probably exists on most modern operating systems.
If you do not have a JRE on your machine, you can download it for free from SUN:
Select "Java Runtime Environment (JRE)", and click download. The next page will then allow you to select your operating system and download the actual installation files.

Download and documentation

  • The required crescentTrain.jar for a Java 5 runtime environment. (Version from 26.3.2008)
  • The CrescentTrain.pdf documentation file, which explains all the keys and command-line parameters.

    Programm history

    26.03.2008 Using supersampling to make the crescent smoother
    25.03.2008 Initial version

    Known limitations

  • The crescent is just a uniform disk, no drop of brightness towards the terminator, no structures. These real-world properties make the task more difficult, which can easily be simulated by reducing the brightness of the crescent.


    Start screen, displaying a short description and list of keys.

    The crescent revealed, by pressing the "r" key.

    Daytime crescent, with blue sky.
    Startup parameters: rSky=150 gSky=150 bSky=220 gradient=0 orientation=-45

    Strong gradient, narrow field of view, big cescent left of the middle, pointing left.
    Startup parameters: gradient=200 field=1.0 orientation=65.0

    Wider field of view = smaller crescent (at the bottom).
    Startup parameters: field=2.5

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