Glossary H

Heliacal Rising. The first visible morning rising of a celestial object on the eastern horizon before sunrise. On the previous day, the object was not visible because it was too close to the Sun. On the following day the object is visible for a bit longer until the brightness of the dawn obliterates it. In ancient times, the heliacal rising of a star or group of stars was one of the main astronomical methods used to determine the seasons. Hesiod, for example, notes the heliacal risings of Arcturus, Orion and the Pleiades.

Heliacal Setting. The last visible evening setting of a celestial object on the western horizon after sunset. On the previous day, the object was more easily visible as it set because it was further away from the Sun. On the following day the object will not be visible because the Sun will be nearer to it and the sky will be too bright. In ancient times, the heliacal setting of a star or group of stars was sometimes used determine the seasons. Hesiod, around 700 BCE for example, notes the heliacal setting of the Pleiades —which happened in late March— in Works and Days (383–7) as the time for sharpening tools.

Hellenistic Era. A conventional period of Greek history which runs from the end of the Persian Wars in 479 BCE to the death of Alexander the Great in 323 BCE. It followed the Classical Era (479 – 323 BCE) and was followed by the Roman Era (146 BCE – 476 CE).

Horizontal Coordinate System.

Hour.

Hour Angle.