Time and location are calculated automatically based on the geographical coordinates and time information obtained from your computer. If you deny access to geographical coordinates, the map will automatically be calculated for an observer based in London.
When you click on the map, it will display the name of the chosen constellation in the dropdown and highlight the whole constellation in a different colour. If the nearest star has a name, this name will also be displayed. You can also select a constellation from the dropdown and this constellation will be highlighted on the map.
The cardinal points can be rotated, therefore the direction of observation modified, by dragging the mouse on the map.
The animation buttons allow you to make time change automatically by minutes, days or sidereal days. A sidereal day is the time required for one rotation of the Earth (23 hours 56 minutes), which allows you to freeze the apparent motion of the stars.
Date and time can be updated. The time must be local to the observer. The date format needs to be day-month-year and the local time format must be hours-minutes-seconds. The year has to be between 1600 and 2400. To force daylight saving time, click on that check box. The « Now » button reinitialises time with the time provided by your computer.
If the location has been calculated automatically, the city dropdown displays dashes. To change the observer’s location, you can either enter the decimal longitude and latitude and a time zone or choose a city from the dropdown. Longitude is positive for places to the East of London and latitude is positive in the Northern hemisphere. The time zone is the time difference in hours relative to Greenwich Mean Time (GMT). It is independent of daylight saving time and for instance 0 for London, +1 for Paris or -5 for New York
The display can be updated to show or hide the ecliptic plane, the celestial equator, a grid of local coordinates, the outline of constellations, the names of the constellations and to change the colour of the map. A dropdown also allows you to change the language of the map.
Version 1.6.2 (19/08/2020): Animation speed control.
Version 1.6.1 (11/09/2018): Magnitude control and layout change.
Version 1.6.0 (17/09/2016): Ability to rotate the cardinal points by dragging the mouse.
Version 1.5.0 (01/11/2015): Automated geolocation.
Version 1.4.0 (25/10/2015): Dynamic size of the map, support for high definition and retina displays.