Chandrayan Vrat is not so known fast but it's an age-old practice to enlighten our Mind, Body and Soul

In olden times Rishi or Sage would do Chandrayan Vrat, it is more of Sadhna or Spiritual practice which eventually takes us to perfection, contemplation, purification, and the correct way of living life. Some people also call it Intermittent Lunar fasting. It can work as a Vedic Solution for most of our current lifestyle-related issues. In today’s context, I would say it detoxes the mind and body and ideally it should be done every 6 months. The first time I heard about this Vrat was almost a decade back when my Grandfather started keeping it. That's when I realised probably this is the most powerful Vrat or fast. In this, the Moon’s entire one month cycle and the food that we consume during this time are connected. Basically, we adjust the food portions as per the Moon’s phases during the entire 30 days cycle.  

Why is this connected to Moon?

According to astrology Moon symbolises our Subconscious mind, Liquid in our body and Spiritual nature.  It governs the Mind, Emotions and Innate nature. The moon controls the food energy, so much that traditionally in the eastern region farmers used to sow seeds on the full moon day. That's why if you have ever noticed when we eat on the full moon our body feels energetic, while on no moon day we feel less energy in our body.  The fact that our Vedic astrology is largely based on Moon proves its importance in ancient times. In Vedic astrology, the moon in the waxing phase (from no moon to full moon) at the time of birth was regarded as a highly favourable time zone. If you want to know more about Moon and the related Puja visit Askganesha puja Homam  

Chandrayan Vrat as explained in our Puranas

It is an extremely tough fast but considered worthwhile to undertake this fast.  There is a strong belief in Puranas that Chandrayan Vrat eliminates all our sins, and releases the body's disease. In fact, in astrology, Chandrayan Vrat is advised to seek penance from God. Performed as per our Vedic astrology calendar which in itself is largely based on the Moon. It is observed for a month following the moon phases in one cycle,  along with Gayatri Mantra Jaap every day. The Vrat ends with Hawan and a charity for needy people. People believed that those who continue to perform this Vrat every month, get moksha in the end. There are 12 Chandra maas or Lunar months as per Hindu Calendar. Amongst all Kartik month which is in 8th place is the most auspicious month to keep this Vrat. Besides Kartik month is also regarded as a righteous time to Donate, and to perform tulsi puja and Narayan puja.  

There are four kinds of Chandrayan Vrat

• Pipilika Madhya   
• Yavamadhya
• Yati Chandrayan  
• Sisu Chandrayan

The food quantity can be adjusted according to the type of Chandrayan Vrat you are doing for e.g in Yati and Shishu Chandrayan Vrat there is no need to increase or decrease the food portion quantity. 

There are two principal ways to perform this puja 

Shukla Paksha or Waxing Moon

Start the next day of Amavasya on the Pratipad of Shukla Paksha or Waxing Moon, eat only one morsel or one-bite portion. On the second day, two morsels and thereon increase one morsel each day till 14 or 15 morsels on the Purnima day. And after Purnima from the next day starts reducing one morsel each day like 14 morsels, then 13 and so on with the reducing phase of Moon or Wanning moon or Krishna Paksha. And finally, on Amavasya preserve complete fast. For exact moon phases check with your astrologer.

Krishna Paksha or Wanning Moon

This one starts and ends on Purnima or Krishna paksha Pratipad or Wanning Moon. In this you divide the meal into 15 morsels, first day on Purnima take the full 15 or 16 morsels and then reduce it every day by one morsel. And finally, on Amavasya don't eat anything. Then the next day onwards we start with one morsel, then 2 morsels and continue to increase take it to 15 or 16 morsels on Purnima day following the waxing phase of Moon or Shukla Paksha.   The morsels must always be adjusted according to the tithis or dates. Because, as per Vedic year many times there are changes in Tithi or Hindu calendar dates of Moon phases.  In fact, the size of the morsels is also mentioned in Puranas. The morsel can not be more than the size of a chicken egg, a peacock egg or a big sized amla.    Chandrayna Vrat along with Yoga, pranayam, and meditation helps to take complete control over the mind, leading to de-addiction, a disciplined lifestyle. wonderful life-changing habits. It develops concentration and brings wonderful life-changing habits into our life.    

Steps to observe Chandryan Vrat

1. Place an idol of Lord Chandra and Goddess Rohini in a cleanroom. Then, you must get Pran           Pratishthitha done. Also, keep Gayatri Yantra at the place of puja. 
2. On the first day of the fast, you must start with Panch Devta Puja and then Maa Gayatri, Lord Chandra and Maa Rohini puja.
3. Then, after taking Sankalp and saying your wish from the Vrat you can start the Chandrayan Vrat.
4. However, it is important to keep in mind that your wish from this Vrat should not be any materialistic pursuits. As this powerful Vrat is meant only for purification from any sins committed.
5. The people observing Chandrayan Vrat have to follow complete celibacy during this fast. One should not have any negative feelings toward others only pure thoughts should be in mind. 
6. During Chandrayan Vrat Gayatri Mantra should be chanted with 40 prayer beads or at least 11beads every day. At the end of the fast, one and a half lakh Gayatri Mantra chanting rituals should be completed.
7.  It is important that only 'Havishya Ann' means food used for giving Ahuti in Havana like Ghee, rice, sesame seeds, Moong, cows Ghee, milk and yoghurt etc should be consumed.  
8. The Person who keeps fast should sleep on the ground

To complete the Chandrayan Vrat the fasting person must perform Gayatri Havan of 1100 Ahuti and give donations to the needy people. Although Purana says to donate a cow for Chandryan Vrat, instead you can also donate money for the well being of the cow to a Gaushala or Cow Shed.  Apart from this, those who want can also donate Gayatri Yantras, Silver, Gems, etc.    If you are planning to observe Chandrayan Fast consult an Astrologer and I would also suggest speaking to your health physician to understand your health capacity.