Today's Panchang in London

Panchang (also spelled Panchangam) means five limbs: the five things a Hindu almanac states for each day. They are the tithi (lunar day), the vara (weekday), the nakshatra (the star group the Moon is in), the yoga (a measure of the Sun and Moon together) and the karana (half a tithi). Around them an almanac lists sunrise and sunset and the timed periods of the day, such as Rahu Kaal, Choghadiya, Hora and Abhijit Muhurat.

It is used to choose a day and a time for ceremonies, journeys and beginnings, and to know which festival or fast falls on which date.

Tithi: the Moon gains 12 degrees on the Sun for each tithi, so a lunar month has 30. The 15 tithis from the new Moon are the bright fortnight (Shukla paksha), ending with Purnima, the full Moon; the next 15 are the dark fortnight (Krishna paksha), ending with Amavasya, the new Moon. A tithi lasts roughly 19 to 26 hours, so it begins and ends at any time of day.

Vara: the weekday. In the Panchang the day starts at sunrise, not at midnight.

Nakshatra: the Moon travels through 27 nakshatras, each 13 degrees 20 minutes of the zodiac, and stays in each for about a day.

Yoga: the sum of the Sun's and Moon's longitudes, divided into 27 parts of 13 degrees 20 minutes. There are 27 yogas, from Vishkambha to Vaidhriti.

Karana: half a tithi, so 60 in a lunar month, from 11 names: seven that repeat and four that occur once a month.

The Moon's position is the same for everyone at the same instant, but the Panchang day starts at the local sunrise and every period is a fraction of the local day, so the clock times, and sometimes which tithi is current at sunrise, depend on where you are. Use the Panchang of the place where you are, or where the ceremony will be.

Sunrise, sunset, moonrise and moonset come from the Navamsha astrology API; where it is not available they are computed by our own engine, which agrees with it to a fraction of a second. The moment each tithi, nakshatra, yoga and karana ends is computed by that engine from the positions of the Sun and Moon (NASA JPL DE421 ephemeris) in the sidereal zodiac with the Lahiri ayanamsa. Rahu Kaal, Choghadiya, Hora, Abhijit Muhurat and the other periods are fixed fractions of the day worked out from sunrise and sunset.

Almanacs differ in how they define sunrise. Here the Sun rises when the centre of its disc is on the horizon, with no allowance for refraction. Almanacs that use the Sun's upper edge and refraction show sunrise a few minutes earlier and sunset a few minutes later, and their Rahu Kaal and other periods move with it. For a ceremony, follow the Panchang your family priest or local temple uses.

London is far north, so its summer days are very long and its winter days short, which stretches and squeezes every Panchang period; it also changes its clocks in March and October.