This Java applet allows you to see what the sky would look like at a given time from any place on Earth. It shows the position of the Sun, the Moon, Mercury, Venus, Mars, Jupiter, Saturn, as well as 1377 bright stars. To identify a constellation, just click on it. Note that the Sun, the Moon and the planets are displayed much larger than in reality. The size of the Sun or the Moon, for instance, should only be a little more than one pixel.
All the algorithms used are based on the book ‘Calculs astronomiques à l’usage des amateurs’, Jean Meeus, Société astronomique de France, Paris, 1986, a translation of ‘Astronomical formulae for calculators’, Jean Meeus, Willmann-Bell.
In case of problem or question, have a look at the online help below or contact me.
Some notes about the control panel :
The positions of the objects on the screen are refreshed every time you change a field, choose a city in the list or click a check box.
The date format needs to be : day month year, and the local time format must be : hours minutes seconds. The year itself has to be between 1600 and 2400.
The time zone is the time difference in hours relative to Greenwich Mean Time (GMT). It is for instance 0 for the London, +1 for Paris or -5 for New York.
To take into account Daylight Saving Time (aka Summer Time) when required, click on the check box below the time zone. In the European Union, for example, this box needs to be clicked between the end of March and the end of October.
To select an observation site, you can either choose a main city from the list, or enter a longitude and latitude (both in degrees and minutes) yourself. Longitude is negative for places to the East of London and latitude is negative in the southern hemisphere. Don’t forget to change the time zone if you are not selecting from the list.
The last check boxes allow you to display or hide the ecliptic plane, the celestial equator, the names of the constellations, and to change the color of the applet.