Suncalc
Suncalc models the relationship between the date, time of day, the geographic location of a place, and the position of the sun in the sky, together with the length & direction of the shadows it casts.
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Suncalc models the relationship between the date, time of day, the geographic location of a place, and the position of the sun in the sky, together with the length & direction of the shadows it casts.
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https://www.suncalc.org
SunCalc can be used for geolocation and chronolocation in various ways:
Location of a chosen point on the earth's surface
Date
Time of Day
Height of an object at the chosen point (for shadow calculation)
Establishing the Time/Timeframe of Source Imagery: When dealing with research imagery sourced from social media, remember that the time at which an image was taken is not necessarily the time at which it was posted on social media, which could be any time after it was created. Sometimes regional internet blackouts are imposed where the authorities wish to prevent publication of current affairs, and this makes reconstruction of event timing particularly difficult. Many social media platforms strip metadata like the time the image was taken before publishing. This metadata is less likely to be deleted if images are sent using a platform's file transfer service, rather than being "posted".
The red centre circle shows the selected location over the map, with horizontal and vertical crosswires for accuracy.
The sun is shown over the earth as an orange disc.
The thin yellow curve is the trajectory of the sun for the chosen location and date
The shaded yellow arc (crescent moon shape) shows all the sun's trajectories superimposed for the entire year, i.e. the variation of the sun's path over the year.
The two coloured radial lines are the position of the sun at sunrise (lighter yellow in the East) and the position of the sun at sunset (darker orange in the West).
Menu buttons top left and top right of the map display show menus to toggle overlays for night, eclipse, and date and for distance measurement (Top Left Option Icon) and to set the source of the base map from 4 options (Top Right Layer Icon). See menus above.
Open Source Imagery often contains shadows in the same image as the object which cast them. Trigonometry can be used to relate the height of the object, the length of the shadow and the angle of elevation of the sun. It is the elevation angle of the sun which determines the ratio of the height of an object to the height of the shadow it casts.
These transparent protractor images can also be found online and be transformed in 3D by graphics programs to rotate to an angle which compensates for non-orthogonal shadow images, but some accuracy is lost. Above is a digital protractor in *.png format to preserve transparency so that measurements can be made whilst the image beneath is visible.
SunCalc Shadow Length Function allows the user to input the height of an object at the chosen location, and then displays the length of the shadow of that object for the given location, date and time. This shadow length is displayed above the input window for object height.
To open the input window for shadow length, click on the Object Level text input window in the sidebar, then enter text or use the buttons to set the object height - see above.
This animated graphic is generated by SunCalc for location Eiffel Tower, Paris, France. A still photograph taken from that exact location at a known date and time is shown below for comparison. The last graphic shows how to generate the animated graphic in SunCalc.
SunCalc can run an animation showing the sun's daylight trajectory over time from dawn to dusk for the day and location chosen in the sidebar. This is activated from the Time Input Window as shown above.
Some technical knowledge and practice is required to use Suncalc efficiently. The interface is not always immediately intuitive. For Open Source research, the calculation of shadow lengths and the relationship with the elevation angle can be error-prone.
None. No account is needed.
Accuracy: The main limitation in the use of SunCalc for Open Source investigation is variable accuracy of the results. SunCalc itself is a very accurate tool, but the accuracy of the SunCalc input values obtained in Open Source research is often questionable. For example, taking measurements from imagery is often inexact, e.g. azimuth and elevation sun angles, shadow and object lengths which aren't at 90 degrees to the photographer.
Graphical Interface: Many users find it counterintuitive that the background map in Suncalc can be moved by the user, but the geographic location point cannot. There is good design justification for this, it simply doesn't align with other tools on this point and so requires adjustment from the user.
Torsten Hoffmann, Germany
Sophie Tedling
UTM () co-ordinates
Julian date (), (Difference between Terrestrial Time and Universal Time), Greenwish Mean Sidereal Time (), Greenwich Hour Angle (), Solar , (celestial equivalent of longitude), Date and Time of March, June, September and December
, and
Where a solar eclipse is to take place, this is tracked on the map as a thick purple line with its date.
Beware: For accurate results, the object in a source image and the shadow it casts must be at right angles (i.e. orthogonal) to the camera. A useful tool for dealing with angles in imagery is a transparent digital protractor. The example below can be copied and pasted for personal use and is provided under a creative commons licence by pngall.com at
SunCalc general tutorial (not specifically Open Source research)
The effects of the earth's orbit around the sun at
Real time sun and moon tracking at
Moon calculations at
Planet calculations at
Satellite orbit tracking at
