TzolkʼinTzolkʼin (t͡sol ˈkʼin, formerly and commonly tzolkin) is the name bestowed by Mayanists on the 260-day Mesoamerican calendar originated by the Maya civilization of pre-Columbian Mesoamerica. The tzolkʼin, the basic cycle of the Maya calendar, is a preeminent component in the society and rituals of the ancient and the modern Maya. The tzolkʼin is still used by several Maya communities in the Guatemalan highlands. While its use has been spreading in this region, this practice is opposed by Evangelical Christian converts in some Maya communities.
Ali ibn RidwanAbu'l Hassan Ali ibn Ridwan Al-Misri (أبو الحسن علي بن رضوان المصري) (c. 988 - c. 1061) was an Arab of Egyptian origin who was a physician, astrologer and astronomer, born in Giza. He was a commentator on ancient Greek medicine, and in particular on Galen; his commentary on Galen's Ars Parva was translated by Gerardo Cremonese. However, he is better known for providing the most detailed description of the supernova now known as SN 1006, the brightest stellar event in recorded history, which he observed in the year 1006.
Egyptian astronomyEgyptian astronomy began in prehistoric times, in the Predynastic Period. In the 5th millennium BCE, the stone circles at Nabta Playa may have made use of astronomical alignments. By the time the historical Dynastic Period began in the 3rd millennium BCE, the 365 day period of the Egyptian calendar was already in use, and the observation of stars was important in determining the annual flooding of the Nile. The Egyptian pyramids were carefully aligned towards the pole star, and the temple of Amun-Re at Karnak was aligned on the rising of the midwinter Sun.
Thābit ibn QurraThābit ibn Qurra (full name: Abū al-Ḥasan ibn Zahrūn al-Ḥarrānī al-Ṣābiʾ, أبو الحسن ثابت بن قرة بن زهرون الحراني الصابئ, Thebit/Thebith/Tebit); 826 or 836 – February 19, 901, was a polymath known for his work in mathematics, medicine, astronomy, and translation. He lived in Baghdad in the second half of the ninth century during the time of the Abbasid Caliphate. Thābit ibn Qurra made important discoveries in algebra, geometry, and astronomy. In astronomy, Thābit is considered one of the first reformers of the Ptolemaic system, and in mechanics he was a founder of statics.
