Rahu Kaal: why the time is different every day
Most people remember Rahu Kaal as a fixed hour on a particular weekday. It is not one. It is a fraction of the daylight, which is why it moves through the year and differs between two cities on the same day.
Ask around and you will be told Rahu Kaal is half past four on a Thursday, or half past ten on a Monday. Those numbers are somebody's city, in some particular month, remembered and passed on.
Rahu Kaal is not a clock time. It is a proportion of the day, and that changes everything about how you look it up.
An eighth of the daylight
Take the time between sunrise and sunset and divide it into eight equal parts. One of those eighths is Rahu Kaal. Which one depends only on the day of the week:
| Day | Which eighth |
|---|---|
| Sunday | Eighth |
| Monday | Second |
| Tuesday | Seventh |
| Wednesday | Fifth |
| Thursday | Sixth |
| Friday | Fourth |
| Saturday | Third |
That is the whole calculation. Everything else follows from it.
Why it moves
Because daylight is not a fixed quantity.
In Surat in June the sun is up for about thirteen and a half hours, so an eighth is a little over a hundred minutes. In December it is closer to eighty. The span is a different length and it starts at a different time, because sunrise has moved too.
Two consequences people find surprising:
- Your city matters. Sunrise in Kolkata and sunrise in Ahmedabad are close to an hour apart. A Rahu Kaal calculated for one is simply wrong for the other, even though both are in the same time zone.
- A remembered rule of thumb drifts. It was accurate the month somebody learned it and has been sliding ever since.
This is also why almanacs print Rahu Kaal per city rather than as a national table.
Yamaganda and Gulika
Two other periods work exactly the same way — a different eighth of the same daylight, assigned by a different weekday table. Yamaganda and Gulika Kaal are read the same way as Rahu Kaal and, like it, move with the season.
If you are checking one, it costs nothing to see all three.
What it is actually for
Rahu Kaal is traditionally avoided for beginning things: signing, buying, travelling out, opening, marrying.
It is not a period in which to do nothing. Work already under way continues through it. The distinction is between starting and continuing, and it is the part most often lost.
There is also a counterweight most people are never told about. Abhijit Muhurta — the eighth of fifteen muhurtas of the daylight, straddling solar noon — is the one span of the day considered auspicious by default. If a morning is crowded with periods to avoid, that is the one to aim at.
Look up today's
Our panchang computes all of this for your own place: sunrise and sunset to the minute, all three inauspicious periods, Abhijit and the other favourable muhurtas, and the day's tithi, nakshatra, yoga and karana with the times they end.
It is worked out from an ephemeris rather than a table, so it is right for your city on the day you are asking — which, given that the whole thing is a fraction of your own daylight, is the only way it can be right at all.