I first bow down to my guru and take their aajna (permission).
1. Sankathara chaturthi vrata
According to smriti kaustubha, the sankanthara vrata has to be done without eating food. The common vrata paribhasha says, "Drinking too much fluid (often, even water), eating tobacco, or betel nuts, or betel leaves, or any other activity prohibited by vrata" will break the fast. Now smriti kaustubha grantha says that the vratha has to be broken at the moonrise time after doing puja to ganesha and argya to ganesha. One needs to celibate during vrata period. One can drink water but not too often. One cannot smoke or consume alchohol or eat meat of anykind during vrata or after breaking the fast, and the fast cannot be broken with meat products.
2. Now question comes what happens when you are in your monthly menstrual period?
The Nirnaysindhukar clearly addresses this issue by saying, whenever sutaka (ashoucha) appears one can continue doing vrata by following sharirika dharma. It means you can keep fast. Do manasika (in your mind) puja but actual puja can be performed on your behalf by a brahmin or your family member. They can take sankalpa on your behalf. If your vrata involves giving alms or other thing that can be done after the ashucha period is over.
3. When to break fast?
At the time of moonrise, one can perform ganesha puja and give arghya water to moon. Now comes the trick what if moon is not visible due to clouds? Similar situation arises during surya/chandra grahana. Tithinirnay and other grantha says, "Grahana Punyahkala exists if grahana is visible". This has to be understood properly. It means if it's visible in your area then do all punyakala. It adds further.... "if grahana is not visible due to megha (rain), clouds or other things, refer to the shatrokta ganita and find out sparsha and moksha timings and then do punyahkala things needs to be done". This clearly mentions that we are unable to see the eclipse due to clouds, but one can verify and one has to verify that eclipse or that celestial body has risen by making sure it's a grahana or celestial body's rising time. This is because any other celstial body may appear and look like moon. The similar story is said in karwa chauth vrata katha where "brothers light artificial fire and tells their sister that moon has risen and she breaks fast without verifing with shastra thus incurring wrath". It's very difficult for a normal person to calculate moon rise times and sparsha, moksha time for eclipse. The daily newspaper will give sunrise, sunset, moonrise and eclipse timings (if it's happening). One can note down and then wait for moon to appear. If it doesn't appear within an hour one can do ganesh puja and then make a picture of moon or with the help of rice make moon and give arghya. This is completely shastroka as per sankathara chaturthi vrata katha. Sometimes one can call friends in neighbouring city to check if they have seen moon but after verifying shastroka moonrise time from the ephemeries. Now many online ephemeries are available to find out actual moonrise time. It will take roughly half an hour for moon to appear as the moonrise timing mentioned in the ephemeries are usually the upper limb visible on the horizon. Now you cannot take moonrise time of India and break your fast. This is completely illegal. That's because i've already explained that the moonrise time mentioned is the upper limb visiblity on the horizon. This horizon differs from place to place, city to city. The best way is to visit http://www.mypanchang.com/ and click on "panchangam/calendar" then scroll down to your city and click on either amavasyant or poornimant calendar. Then click on the month on top and go down to the date. You will see moonrise: and the time.
Following mantra is from Pandit Kashinath Upadhyay's Dharmasindhu and similar verses is found in Nirnay sindhu, smriti kaustubha, and Tithi Nirnay about what to do when the eclipse is not visible due to clouds. So we can take same for other celestial bodies as visibility is the principle behind both this situations.
Here it's clearly mentioned that when the grahana is not visible due to clouds one can get "sparsha" / "moksha" kala from ephemeries and observe grahana and do punya. Likewise The same rule can be applied to all vratas which requires 'observance' or seeing the particular celestial body.
4. When to start this vratam.
Sharvan krishna paksha chaturthi or angaraki (when sankathara chaturthi appears on tuesday). This vrat can be observed for 21 sankathara chaturthi or life time.
5. Sankathara chaturthi vrata katha?
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