Lagna = Rising sign at birth = 1st House

Lagna shifts ~1 Rashi every 2 hours as Earth rotates

12 Rashis × 2 hours = 24 hours = full rotation

Whole-Sign System (Vedic standard):

If Lagna is in Mesha (Aries) → 1st house = all of Mesha (0°-30°)

2nd house = all of Vrishabha (Taurus) 30°-60°

...and so on for all 12 houses

Placidus System (KP method):

Houses = unequal arcs based on time-based trisection

House cusps calculated from LST and geographic latitude

LST (Local Sidereal Time) = GST + Longitude/15

Lagna longitude = atan(sin(LST) / (cos(LST) × cos(ε) - tan(φ) × sin(ε)))

where ε = obliquity (~23.44°), φ = geographic latitude