- Northern celestial hemisphere (Wikipedia)
The northern celestial hemisphere, also called the Northern Sky, is the northern half of the celestial sphere; that is, it lies north of the celestial equator. This arbitrary sphere appears to rotate westward around a polar axis due to Earth’s rotation.
- Southern celestial hemisphere (Wikipedia)
The southern celestial hemisphere, also called the Southern Sky, is the southern half of the celestial sphere; that is, it lies south of the celestial equator. This arbitrary sphere, on which seemingly fixed stars form constellations, appears to rotate westward around a polar axis due to Earth’s rotation.
- Ptolemy (Wikipedia)
Claudius Ptolemy (/ˈtɒləmi/; Greek: Πτολεμαῖος, Ptolemaios; Latin: Claudius Ptolemaeus; c. 100 – c. 170 AD) was a Roman mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importance to later Byzantine, Islamic, and Western European science. The first is the astronomical treatise now known as the Almagest, although it was originally entitled the Mathēmatikē Syntaxis or Mathematical Treatise, and later known as The Greatest Treatise. The second is the Geography, which is a thorough discussion on maps and the geographic knowledge of the Greco-Roman world. The third is the astrological treatise in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day. This is sometimes known as the Apotelesmatika (lit. “On the Effects”) but more commonly known as the Tetrábiblos, from the Koine Greek meaning “Four Books”, or by its Latin equivalent Quadripartite.
- Aquila is a constellation on the celestial equator. Its name is Latin for ’eagle’ and it represents the bird that carried Zeus/Jupiter’s thunderbolts in Greek-Roman mythology.
- Eta Aquilae (Wikipedia)
Eta Aquilae (η Aql, η Aquilae) is a multiple star in the equatorial constellation of Aquila, the eagle. It was once part of the former constellation Antinous. Its apparent visual magnitude varies between 3.49 and 4.3, making it one of the brighter members of Aquila. Based upon parallax measurements made by the Gaia spacecraft on its third data release (DR3), this star is located at a distance of roughly 272 parsecs (890 light-years). The primary component is a Classical Cepheid variable.
- Altair (Wikipedia)
Altair is the brightest star in the constellation of Aquila and the twelfth-brightest star in the night sky. It has the Bayer designation Alpha Aquilae, which is Latinised from α Aquilae and abbreviated Alpha Aql or α Aql. Altair is an A-type main-sequence star with an apparent visual magnitude of 0.77 and is one of the vertices of the Summer Triangle asterism; the other two vertices are marked by Deneb and Vega. It is located at a distance of 16.7 light-years (5.1 parsecs) from the Sun. Altair is currently in the G-cloud—a nearby interstellar cloud, an accumulation of gas and dust.
