ZET comes with a database of 9 100 stars which are utilized in creating the Sky tableau and the background of the Cosmos tableau - and which can be applied astrologically. The optional add-in Hipparcos Star Catalog which can be downloaded here allows 200 000 stars to be displayed in the Cosmos and Sky tableaux.

Astrological usage of stars in ZET is controlled thru the many options available in the Chart Settings - Stars window. The Cosmos and Sky tableaux have separate settings in their own Settings windows.

In contrast to planets, ZET does not automatically update the positions of stars whenever dates or times change - for example with new event data, under animation with Dynamics of Time or Location, etc - unless the option to do so has been explicitly set (see General Settings, Misc tab). This feature allows ZET to work efficiently on a wide range of computers.

Due to several astronomical phenomena the positional coordinates of the so-called 'fixed' stars tend to drift with time. This is due not only to precession (57 arc-seconds per year), but also to the different movements of individual stars (arc-seconds, and fractions of arc-seconds per year). While in absolute terms the drift is not large, it is nevertheless significant in comparison to the precision of calculation employed in ZET. Since a tableau may use potentially many objects in its display, recalculating stellar coordinates to update them to the Epoch of the event data can take up significant computing resource. The facility exists, therefore, to effect the updating of stars' positions under user control.

ZET tracks the accumulated precession, and when the lag, etc becomes significant, the Star precession indicator on the Status bar is activated (see the graphic here). If you pause the mouse pointer over the indicator, a popup tooltip displays the precession, e.g. "Precession has reached 0°0'57 - click to recalculate stars". If you require immediate full correction for precession, click the indicator button.

See also: Star Catalog, Planet - Star Conjunctions, Constellations.