What is a karana?
A karana is half a tithi: a 6-degree interval in the Moon's lead over the Sun.
STEP 1
Count half-tithis
Subtract the Sun's longitude from the Moon's and keep the result between 0° and less than 360°, adding 360° if needed. Divide by 6°. A cycle of 30 tithis therefore contains 60 half-tithi intervals. Exactly 360° starts the cycle again.
STEP 2
Understand the repeating names
The 60 intervals use eleven names. Count from the start of the light half, Shukla paksha. Interval 1 has a fixed karana. Intervals 2–57 repeat seven names, starting with Bava, eight times. Intervals 58–60 hold the other three fixed karanas. The four fixed positions therefore straddle the cycle boundary.
STEP 3
Work an example
A gap of 26° contains four complete 6° intervals and 2° more, placing it in interval 5. This is the first half of tithi 3. The full tithi runs from 24° to less than 36°; its first half ends before 30°, where the second half begins.
STEP 4
Check the name table
Interval 5 is the fourth recurring karana, because Bava starts at interval 2. Use your panchang's name table to identify it. When checking the pattern, mark positions 1 and 58–60 as fixed, and positions 2–57 as recurring.