To create a graphics skin for AstroClock the following set of graphics are required.
All images (except the icon) should be of the same resolution and should have a transparent background.

Background rings

The radius of the clock is divided into 4 equal parts.
The outer 3 parts are each used for a ring.
The diameter of the empty circle in the middle is twice the width of a ring.

Year

The outer ring shows the position of the seasons. Mid summer should be placed at the 12 o'clock position.
Spring is on the right side, autumn is on the left side and winter is at the bottom of the ring.
On the southern hemisphere the pointer is rotated 180 degrees and the image is left unchanged.

Moon

The middle ring shows the phase of the moon. Full moon should be placed at the 12 o'clock position.
On the southern hemisphere the moon phases are reversed so the image will be mirrored along the vertical axis and the clock hand will continue to move in clockwise direction.

Day

The inner ring shows the position of the sun during a day. Mid day should be placed at the 12 o'clock position.

Hands

The values for each ring can be displayed by moving the hands at different speeds in clockwise direction or by moving the rings at different speeds in counter clockwise direction.

Hand rotation

For each ring an image should be created to indicates its current value.
The hand should probably start at the center and end at the ring which it serves.
It could also be possible to start at the outer edge of the clock and have the hands point inwards.

Ring rotation

In this display mode only a single pointer is required to indicate that the part of the ring at the 12 o'clock position, is the current value for that ring.

Indicators

Indicators do not move around a great deal and only serve as a demarcation between certain parts of a ring.

Sunrise/Sunset

These indicators are placed between the day and night part of the inner ring.
As the length of day varies during a year, these indicators move too.

Equinox

These indicators are placed at the spring and autumn equinoxes in the outer ring.
The current version of AstroClock does not show these yet.

Icon

To be able to easily identify a skin, an icon should be provided of 48x48 pixels.