The flag of Turkey (Turkish: Türk bayrağı) (meaning: Turkish flag) is a red flag with a white crescent moon and a star in its centre. The flag is called Ay-yıldız (moon-star) or Al bayrak (red flag). The Turkish flag is referred to as Al sancak (red banner) in the Turkish national anthem. The geometric proportions of the flag were legally standardised with the Turkish Flag Law in 1936 during the republic period of Turkey.
The current design of the Turkish flag is directly derived from the late Ottoman flag, which had acquired its final form in 1844. IOttomans used several different designs, most of them featuring one or more crescents, for different purposes, such as the flag with green background signifying the caliphate. During the late imperial period, the distinctive use of the color red for secular and green for religious institutions became an established practice. In 1844, the eight-pointed star was replaced with a five-pointed star and the flag reached the form of the present Turkish flag; Red was the colour of the Western Turks. In the 14th century red became the colour of the Ottoman Empire. Star and crescent There's a saying that after the Battle of Kosovo -1389, Sultan Murad visited the battle field, and all he saw was a field all in red because of the blood and the star next to it. Some say the Sultan Murad was in tears with the scene right before his eyes, and the reflection of the moon and the star in the bloody field inspired the idea for the flag of the victorious Ottoman Empire.source: wikipedia