Heliacal setting

• A star rises approximately one degree further to the west each day, until it is no longer visible, because it has sunk below the horizon. This is known as its Heliacal setting.

Heliacal Rising and Setting

• Following a period when a star or Planet has not been visible, its first appearance on the eastern horizon just before sunrise is known as its Heliacal Rising.

• From this moment onwards, the star will rise earlier and stay visible for longer before sunrise.
• A star rises approximately one degree further to the west each day, until it is no longer visible, because it has sunk below the horizon. This is known as its Heliacal setting.

• One year later, the same star will rise again in exactly the same position, but the day and time may vary, because its observation will depend on the weather conditions.

Heliacal Rising of Sirius

• The Ancient Egyptian Calendar was based on the Heliacal Rising of Sirius.
• The Ancient Babylonians, the Ancient Egyptians, the Ancient Greeks and the Ancient Romans all kept records of the Heliacal Rising and Heliacal setting of the major Planets and stars, in particular, of [Sirius]].