Positions of the Moon and major planets
This plot shows the whole of the celestial equator and a band of 30 degrees north and south of it. It is plotted in such a way that the Sun is always at both ends. The top scale shows right ascension (RA) and the bottom scale shows elongation in degrees eastwards from the Sun. Elongation 180° is the meridian at midnight. Any planet on the meridian is at opposition.
Initial letters are used for identifying the planets. The 2 M's are distinguished by Mercury having a small letter and its dot being cyan, whereas Mars is orange.
The short green lines through the Sun are tangents to the horizon at sunrise and sunset for the given latitude. The parallel grey lines are 18 degrees above the horizon, to give a quick indication of areas that will at best be seen in twilight (astronomical twilight ends when the Sun is 18 degrees below the horizon).
The applet attempts to get your latitude from your system, by finding your country code and looking up the mean latitude of that country. However, if that does not work, or it is not accurate enough, you can click the button and enter a different value. The latitude value only affects the angles of the horizon and twilight markers.
The sizes of the Sun and the Moon are exagerrated, so it means nothing if planets appear in front of them (Sun and Moon are always plotted before planets).
The calculation scheme for the planets is based on theory given in "Orbital Motion" (3rd edn) by A.E.Roy, Institute of Physics Publishing, UK, 2002, ISBN 0-85274-229-0. The calculation is only an approximate one because it uses the mean orbital elements (as shown for example on NASA's fact sheets). This is accurate enough for this small image display and for a few decades around the present time. It is probably not useful for dates many centuries from the present.
The position and phase of the Moon are calculated using Chapront's theory as described in Chapters 47 and 48 of Astronomical Algorithms by Jean Meeus (2nd Edition).