What is a muhurta as a unit of time?
A muhurta, as a unit of time, is one fifteenth of the daylight period, about 48 minutes when the day is 12 hours long. The same name is used for the choice of an auspicious time.
What it is
Because the day length changes with the season, a muhurta also changes length. The fifteen muhurtas of the day are equal parts of the sunrise-to-sunset interval, and the night has its own muhurtas.
How it is worked out or read
The panchang computes the muhurtas from the day's sunrise and sunset, which is how Abhijit and Rahu Kaal are found.
Where it appears on this site
The panchang shows Abhijit and Rahu Kaal. See muhurat meaning.
Muhurta as a unit and as a choice
The word muhurta has two meanings in Jyotish. As a unit it is one fifteenth of the daylight period, roughly 48 minutes on a twelve-hour day. As a choice it is an auspicious time selected for an activity. The unit is a measure of time, and the choice is a judgement made with several factors. The two meanings are linked, because the choice is often made from the unit: a reader may look for the muhurtas of the day that are favourable and then choose one of them.
Why the unit changes with the season
Because the day is divided into equal parts of the daylight, the muhurta length changes with the season. On a long summer day the muhurtas are longer, and on a short winter day they are shorter. This is why the panchang computes the muhurtas from the actual sunrise and sunset of each date. A fixed clock-time table would be wrong for most of the year, and the traditional method avoids that by working from the day's own length.
Using the unit without the choice
A reader may use the unit alone, to know where the traditional windows fall on a given day, without applying any muhurta rule. The panchang shows Abhijit and Rahu Kaal for this purpose. Knowing where these windows fall is useful for planning, even if the reader does not follow the full muhurta tradition. The learn articles on Abhijit and Rahu Kaal explain each window.
The unit in everyday planning
The muhurta as a unit helps a planner divide a day into a traditional set of windows. Because the windows are fractions of the daylight, a planner who knows the sunrise and sunset can calculate them easily, and can plan around the windows that the tradition considers favourable.
Muhurta and the sense of a good moment
The traditional idea of a good moment is an attempt to match human activity to the rhythm of the day. A reader may describe the muhurta as a way of noticing when the day's light and the chosen activity are in harmony, while recognising that the choice remains a human judgement.
Thirty muhurtas
A full day and night together contain thirty muhurtas, fifteen for the day and fifteen for the night.