Planet and Fixed Star Visibility Periods (2020–2030, Istanbul)
Heliacal Rising (first morning)
Cosmic Setting (last morning)
Acronychal Rising (first evening)
Heliacal Setting (last evening)
All heliacal events for the 5 classical planets from 2020 to 2030. Each planet passes through morning star and evening star phases according to its visibility cycle.
Superior Planet Visibility Cycle (☤ ♃ ♂)
1Heliacal Setting Disappears from the evening sky (approaching conjunction)
↓ invisible period (under the Sun’s beams)
2Heliacal Rising First visible in the morning sky
↓ morning star period
3Acronychal Rising Becomes visible in the evening sky as well (approaching opposition)
↓ visible all night (near opposition)
4Cosmic Setting Disappears from the morning sky, visible only in the evening
↓ evening star period → back to heliacal setting
Inferior Planet Visibility Cycle (♀ ☿)
1Heliacal Setting Disappears from the evening sky (approaching superior conjunction)
↓ invisible period (superior conjunction)
2Heliacal Rising Visible in the morning sky (morning star)
↓ morning star period
3Cosmic Setting Disappears from the morning sky (approaching inferior conjunction)
↓ invisible period (inferior conjunction)
4Acronychal Rising Visible in the evening sky (evening star)
↓ evening star period → back to heliacal setting
Annual heliacal rising dates for 15 prominent fixed stars. Fixed stars rise heliacally on approximately the same date each year. These dates served as critical calendar and agricultural reference points in the ancient world.
Star
Magnitude
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
Sirius and the Nile Flood: The ancient Egyptian calendar was based on the heliacal rising of Sirius (Sopdet/Sothis). The heliacal rising of Sirius heralded the annual flooding of the Nile and was regarded as the beginning of the Egyptian year. At Cairo (~30° N) this date falls in early August. Due to Istanbul’s higher latitude (41° N), the heliacal rising of Sirius shifts to mid-August.
Bar chart showing the visibility status of planets throughout the year. Yellow regions represent morning visibility (from heliacal rising to cosmic setting), green regions represent evening visibility (from acronychal rising to heliacal setting).
Morning Star
Evening Star
Invisible
Note: Istanbul’s latitude (41° N) directly affects planetary visibility. The angle between the ecliptic plane and the horizon varies from season to season. In the morning sky, the spring ecliptic is steep while the autumn ecliptic is shallow. Therefore, a planet with the same elongation is more easily visible in spring, but may remain below the horizon in autumn. The delay of Saturn’s spring heliacal rising up to ~40° elongation is caused by this effect.
Heliacal Rising (φάσις ἑὥα / Heliacal Rising): The moment when a celestial body, after being invisible for an extended period due to conjunction with the Sun, first becomes visible to the naked eye on the eastern horizon just before dawn. The Sun must be sufficiently below the horizon (arcus visionis) and the body must be above the horizon. In classical astrology, this moment is interpreted as a planet gaining strength.
Cosmic Setting (κοσμική δύσις / Cosmic Setting): The moment when a body visible in the morning sky is last seen on the morning horizon as it approaches the Sun. The body “sets” with the Sun, i.e., it disappears in the dawn light. It is the opposite of heliacal rising: the end of morning visibility.
Acronychal Rising (ἀκρόνυχος ἀνατολή / Acronychal Rising): The moment when a celestial body “rises” on the evening horizon as the Sun sets. The body becomes visible in the evening sky for the first time. For superior planets, this signals the approach of opposition. For fixed stars, it marks the beginning of the period when the star is visible throughout the night.
Heliacal Setting (κρύψις ἑσπερία / Heliacal Setting): The moment when a celestial body is last visible to the naked eye on the evening horizon as it approaches the Sun. After this moment, the body disappears under the Sun’s beams and remains invisible for a period. It is considered a temporary loss of planetary strength.
Arcus Visionis (Visibility Arc): The minimum angle the Sun must be below the horizon for a celestial body to be visible to the naked eye. This value depends on the body’s brightness. Brighter bodies require less darkness:
Significance in classical astrology: Ptolemy considers a planet’s heliacal condition (whether it is a morning star or evening star, visible or invisible) as one of the fundamental factors determining its strength. A planet that has made a heliacal rising (risen as a morning star) is considered empowered. A planet under the Sun’s beams (burnt/combust) is weakened. Whether Venus and Mercury are morning or evening stars changes their nature: morning Venus is interpreted as more measured and disciplined, while evening Venus is more passionate and exuberant.
Accuracy note: This calendar has been computed using the astronomy-engine library for Istanbul coordinates (41.01° N, 28.98° E). Dates are accurate to ±1–2 days. Actual visibility depends on atmospheric conditions (humidity, dust, light pollution), the observer’s altitude and horizon clarity. Arcus visionis values follow the Ptolemy and Schoch tradition; different sources may give slightly different values.
Sources & Method
Heliacal dates have been computed using the astronomy-engine library for Istanbul (41.01° N, 28.98° E). For each day, the altitude of the body above the horizon was checked at the moment the Sun reached the arcus visionis depth (>2° threshold). Fixed star coordinates were calculated from the J2000 epoch with precession correction.
Ptolemy, Tetrabiblos and Almagest (2nd c. AD) · Paulus Alexandrinus, Introductory Matters (4th c. AD) · Abu Ma’shar, Kitab al-Mudkhal al-Kabir (9th c.) · Al-Biruni, Kitab al-Tafhim (11th c.) · F.K. Schoch, Planeten-Tafeln für Jedermann (1927) · Jean Meeus, Astronomical Algorithms (1991)