The earth revolves around its own axis once in a day. As a result, we, stationed on Earth, see the Sun rising in the east and setting in the west everyday. The earth also goes round around the Sun in a year and so the Sun appears to travel in the sky once in a year with respect to fixed stars. The earth takes 365.25 days to complete its rotation. So the Sun appears to move in the sky about one degree per day. In this process it moves through the 12 constellations of stars. The constellations are called the Zodiacal signs or Rasis, each Rasi being 30 degrees of arc in the ecliptic. The transit of the Sun into a Rasi ( zodiacal sign ) in its geocentric travel is having specialty as per Dharma sastras and are days of remembrance of Ancestors. This is called Punyakal or holy period. Jyotishasastra helps in determining the correct day and time of such occurrence. The literal term for this transit is Rasi Sankramanam and it is termed as Sankranti or Solar ingress.
This week on 15 June Sun Transits to Mithuna Rasi ( Sign Of Gemini) which is a Shadasitipunyakala.
The following is my translation of the relevant portions from Dharma Sindhu on Sankranti Nirnaya
In Meshasuryasankramana ( Sun entering Aries) 15 ghatikas ( 6 hours as per modern clocks)before and after the time of transit is Punyakala . In Vrisha (Taurus) 16 ghatikas prior (6 hrs 24 minutes), In Mithuna (Gemini) 16 Ghatikas after, In Karka (Cancer) 30 Ghatikas ( 12 hrs) prior, Simha (Leo) 16 ghatikas prior, Kanya ( Virgo) 16 Gh. after, Tula( Libra ) 15 Ghatikas before and after as in Mesha. , Vrischika( scorpio) 16 Gh. Prior , Dhanu( Sagittarius) 16 Gh after, Makara ( Capricorn) 40 Gh ( 16 Hrs ) after , Kumbha ( Aquarius 16Gh prior, Meena (Pisces) 16 Gh after time of transit is Punya kala
If transit occurs with less than two Ghatikas ( 48 Minutes) to end of day i.e., sunset, then for Mithuna, Kanya, Dhanu, Meena and also Makara,punyakala should be considered prior to transit.
Likewise If transit occurs with less than two Ghatikas ( 48 Minutes) to beginning of day i.e, Sunrise then Punyakala for Vrisha, Simha, Vrischika, Kumbha and Karka should be reckoned after transit
If transit occurs in night :
a ) before midnight second half of previous day is punyakalam
b) after midnight first half of next day is punyakalam
c) exactly midnight both the last half of previous day and first half of next day are punyakalam.
This above is the rule for all sankramas other than Makar and Karka . In case of Makara always next day is punyakalam In case of Karka always previous day is punyakalam
Three Ghatikas( I hr and 12 minutes) after sunset is Sayam Sandhya , if makarasankram occurs at that time, previous day that is the day before the sunset is Punyakaalam.
Three Ghatikas( I hr and 12 minutes) before sunrise is pratasandhya , if Karkasankramanam occurs at that time day after sunrise is punyakalam.
Now we talk about Sankranti danam (Charities during suns transits.)
Mesha: Goat
Vrishabha: Cow
Mithuna: Clothes and food
Karkataka: Grutha dhenu ( milch cow)
Simha: Umbrella and gold
Kanya: House and clothes
Tula: Tila (Sesame seeds) and Buttermilk
Vrischika: Lamp
Dhanu: Clothes
Makara: Firewood and fire
Kumbha: Water and grass fr Cow
Meena: Land Other material suitable for occassion with similar ideas can be given
Sraardha without pinda should be done on all sankrantis. Tarpanam for one’s ancestors shall be done with Til ( Sesame seeds) and water. In addition danas may be given on Sayana Sankranti days as per Ayanamsa ( precession) . The current Ayanamsa is approx 23 degrees . Therefore it should be understood that 23 days prior to the Sankranti date in Panchangam is a parvakala as Sun has apparently entered the Rasi.
The Sankrantis in Vrisha, Simha,Vrischika Kumbha are called Vishnupadapunyakalas. Mithuna,Kanya,Dhanu,meena Samkramanas are called Shadasitipunyakalas. Mesha Tula are called VishuvaPunyakalas(equinoxes) and Makara Karkata are Ayana sankrantis (Solstices). The four varieties are having increasing holiness( Punya) i.e, Shadasitipunyakalas are holier than Vishnupadas, Vishuvas are holier than shadasitis and so on.
If Sankramana falls on the Janma nakshatra( birth star) of a person, he will suffer loss of money and grains. To overcome this bathing should be done with lotus leaves in the water.
Studying and teaching of Vedas should not be done in the night before Sankranti and Day of sankranti or in case of night sankrantis previous days and following night in the case of Vishuva and Ayana sankrantis . This is named as Pakshini Sankranti. The idea is that there should not be reading and teaching for 1 1/2 days.