Twilight -------- This application calculates twilight from sun and moon. This is useful when planning a voyage and specially when out in the wild, be it climbing, hiking or sailing, where twilight is an important feature. If you are looking at the stars or hunting northern lights, best periods will be when there is complete darkness. I wrote 'Twilight' when waiting for the first sun after a long and cold winter on board of a sailboat in the Thule region in northern Greenland. Twilight is licenced free of charge. So you are free to use and share it with others provided that copies are not made or distributed for commercial advantage. Output from ‘Twilight’ may be published provided that acknowledgement is made to ‘Twilight’ and the copyright holder. Please feel free to feed back. Suggestions are welcome. Contact >> http://igloo.sailworks.net Have fun :-) Peter Gallinelli, March 2016 Installation ------------ Twilight is written in Java and so should work on any computer. Just extract the zip file to a suitable location and double-clic the twilight*.jar file to make it start. If nothing happens, you may have to type 'java -jar twilight*.jar' from a console. If it still does not start, check that you have the Java Virtual Machine installed. It can be obtained at no cost from the Java (Oracle) website. Definitions ----------- The solar geometry calculations take into account corrections for time and solar refraction. 'Twilight' is divided into civil, nautical and astronomical twilight. Civil twilight: from sunset to the time at which the sun is 6° below the horizon. At this time, there is enough light for objects to be clearly distinguishable without artificial illumination. Civil twilight is the definition of twilight most widely used by the general public. Navigation by sight is generally possible till the end of civil twilight. Nautical twilight: the time when the centre of the sun is between 6° and 12° below the horizon, and only general or vague outlines of objects are visible, when it is still possible to perceive the horizon. This term goes back to the days when sailing ships navigated by using the stars. The use of a sextant to measure the altitude angle of stars required horizon visibility. Astronomical twilight: the time at which the sun is between 12° and 18° below the horizon. It is that point in time at which the sun starts lightening the sky. During the evening, this is the point where the sky completely turns dark. Available daylight will of course depend very much on weather and cloud cover. Moonshine --------- Once the sun has set and no more twilight is available, moonlight can prove useful. 'Twilight' calculates moon phases and times. Under good weather conditions a visible full moon provides sufficient visibility for navigation and other outdoors activities, particularly when reverberation form ice and snow is available. Solar energy ------------ In addition solar energy calculations can be made for tilted surfaces, e.g. to orient your solar panel. The calculations take into account direct and diffuse solar radiation as well as reflected radiation from the ground (albedo) and obstructions. Practical --------- Clic or clic and drag the graph to select a single day or day sequence to be displayed on the day-banner. Stations can easily be added by creating new station files. They can be edited with any simple text editor (do NOT use Word). The format is straightforward. Have a look into the stations folder. Latitude and longitude coordinates are given in degres and decimals. By convention North is positive and South negative, East positive and West negative. The ':' is reserved for parsing, so avoid using it in names. Obstructions can be taken into account by adding a horizon section. The format is as follows: az = bearing from North [deg] ht = altitude above station [m] dt = distance from station [m] e.g. Shorizon_az:0:80:110:170:180:225:235:255:260:265:270:290:295 Shorizon_ht:500:500:700:600:900:600:0:0:500:600:0:0:600 Shorizon_dt:2000:4000:30000:23000:40000:45000:25000:25000:30000:40000:40000:25000:25000 Technical --------- The sunrise and sunset results should be accurate to within +/- 1 minute for locations between +/- 72° latitude, and within ten minutes outside of those latitudes. The moon calendar should be accurate to within +/- 1 hour. Version History --------------- Version beta 0.4 - added dialog to define geogaphical position : pg 2018-05 - added moon calculations and display : pg 2016-05 - added calendar (leap years) : pg 2016-05 - added dynamic resize functionality : pg 2016-05 - banner only functionality : pg 2016-05 Version beta 0.1 - created March 2016 : pg * * *