Compare how the rising time of the same sign changes across different latitudes.
| Sign |
0° Equator |
30° Cairo |
41° Istanbul |
51° London |
60° Helsinki |
Observation: As latitude increases, signs with long ascension rise even more slowly, while signs with short ascension rise even faster. Near the polar circle, some signs barely rise at all. This is why classical astrologers prefer the Whole Sign house system at high latitudes: house boundaries are not distorted in proportion to the sign's rising time.
Rising Times (Ascensional Times): The time it takes for a sign to fully rise (appear) above the horizon. At the equator, all signs rise in equal time (~2 hours). However, due to the obliquity of the ecliptic (~23.44°) and the observer's latitude, actual rising times vary greatly from sign to sign.
Long Ascension: In the northern hemisphere, signs from Cancer to Sagittarius are of long ascension. These signs rise slowly over the horizon, remaining visible in the sky for a longer period. As latitude increases, Virgo and Libra become the signs with the longest ascension.
Short Ascension: In the northern hemisphere, signs from Capricorn to Gemini are of short ascension. These signs rise quickly over the horizon. In the southern hemisphere, the situation is reversed.
Significance in classical astrology: Rising times form the foundation of many techniques in classical astrology. House sizes (in systems like Porphyry and Alcabitius), profection calculations, primary directions, and planetary ages all rely on rising times. Ptolemy, in the Tetrabiblos, bases commanding and obeying signs on these times: sign pairs with equal rising times are considered "equal in power."
Commanding and Obeying Signs: Sign pairs with equal rising times are symmetrically positioned around the summer solstice axis (0° Cancer / 0° Capricorn). The sign on the summer side "commands," while the one on the winter side "obeys." This concept is closely related to antiscia.
Calculation formulas:
Declination: δ = arcsin(sin(ε) × sin(λ))
Right Ascension: α = atan2(cos(ε) × sin(λ), cos(λ))
Ascensional Difference: AD = arcsin(tan(δ) × tan(φ))
Oblique Ascension: OA = α − AD
ε = obliquity of the ecliptic (23.4393°), λ = ecliptic longitude, φ = geographic latitude, δ = declination