Budha-Aditya Yoga is formed by the conjunction of Budha, Mercury, with Aditya, the Sun, in the same sign. It is read for intelligence, learning, skill in speech and administrative capacity. The combination is extremely common for a straightforward astronomical reason: Mercury never appears more than about twenty-eight degrees from the Sun, so it is in the same sign as the Sun in a large proportion of all charts, and in an adjacent sign otherwise. That frequency is itself a caution about how such combinations should be weighted. The classical qualification here concerns combustion, astangata: a planet too close to the Sun is held to be burnt and weakened, so a Mercury within a few degrees of the Sun may be read as damaged rather than strengthened, and different authorities give different orbs for the effect.
Classical texts do not agree on a single combustion orb: figures commonly cited for Mercury range from about eleven to fourteen degrees of separation from the Sun, narrower still, to roughly thirteen degrees, when Mercury is retrograde, and different authorities apply the rule with different strictness. A further complication is that some later commentators distinguish ordinary combustion from a very close conjunction, within about a degree, which a minority of texts treat as exceptionally intensifying rather than damaging, on the reasoning that a planet all but fused with the Sun shares its light rather than being merely scorched by it; this reading is a minority position not shared by most classical authorities. Because the yoga's strength also depends on Mercury being otherwise undamaged, exaltation in Virgo raises its promised effect above the bare conjunction.