A chelengk was a decoration of the Ottoman Empire... It was a jewelled aigrette consisting of a central flower with leaves and buds, and upward-facing rays. In modern Turkish, a çelenk is a wreath or garland, a circular decoration made from flowers and leaves, usually arranged as an ornament.
A specially-made chelengk was awarded to Horatio Nelson by Sultan Selim III in honour of the Battle of the Nile in 1798. This was the first time that a chelengk was conferred on a non-Ottoman. The usual seven rays were augmented to thirteen, as described in a contemporary letter:
Lord Nelson sporting his chelengk
The Aigrette is a kind of feather; it represents a hand with thirteen fingers, which are of diamonds, and allusive to the thirteen ships taken and destroyed at Alexandria, the size that of a child's hand about six years old when opened;
In Patrick O'Brian's Aubrey–Maturin series of novels, Captain Jack Aubrey is awarded a chelengk by the Sultan after capturing two rebel ships. His chelengk was worn, like Nelson's, on his dress uniform hat and contained hidden clockwork, so that the diamond strands shimmered in the sun.I'm fascinated by the bit about 'hidden clockwork' that caused the strands to move about the center. You can be sure that if I had a chelengk, I would be wearing it on a regular basis.