At the heart of the Nyingma tradition is the practice of Dzogchen.The main practices are emphasized in the three inner tantras of Maha Yoga, Anu Yoga, and Ati Yoga. Ati Yoga is also known as the Great Perfection, or Dzogchen. Dzogchen practitioners who have attained ultimate insight (wisdom) and compassion, a phase in which pure and total presence is stabilized (Trek-chod), are then allowed to practice To-gal.

To-gal is the final practice of Dzogchen. This final practice enables the master yogi or yogini to dissolve his or her physical body into the essence of the elements at the time of death. The master disappears into a body of light becoming the wisdom body, the term is called ‘Ja’-lus or The Rainbow Body, It is considered physical immortality or the highest perfection.

The final process of dissolution of the body happens over varying amounts of time ranging from a short period to many days. During this process the body shrinks dramatically eventually down to only bits of hair, toe-finger nails, and possible nasal septum left behind. Some saints such as the great Milarepa (1050-1123) and Padmasambhava dissolved entirely into light, leaving no relics behind at all. The culmination of one’s life into the rainbow body is widely recognized as a sign of extreme sanctity. The process from these traditions is generally considered to take approximately seven days, during which time the body progressively shrinks in size. This shrinking is proportional and may stop at approximately small child size. The Rainbow Body – The Body of Light is light without shadow; it is awareness without obscurations; it is omniscience; it is pure space. It is the ultimate fruit of spiritual cultivation. The Body of Light represents a complete and total and radical transformation of one’s status of being, a rediscovery of what was primordially present, and this condition is permanent. It is Awareness itself and is dependent on nothing else

      This photo was taken on 2011 by TheNON2
      Terton Chokgyur Lingpa's Rainbow Body

       This photo was taken on 2005 by TheNON2
       HH.Chogye Trichen's Rainbow Body

       This photo was taken on 2009 by TheNON2
        XiRao Khenpo's Rainbow Body

Rainbow body is a level of realization

“Rainbow body” is a phenomenon that when the person died, his body is transformed partially, or totally into five pure lights. This means either the physical body become much smaller than before, and the skin quality become as freshness as a newborn baby, or even left nothing behind. This phenomenon is hard to understand according to modern science, but it has been well documented in history

     This photo was taken on 2011 by TheNON2 
      HH.AChuk Lama's Rainbow body, The body shrink dramatically to
      the smaller size.

       Achuk Lama Rinpoche who manifested the rainbow body in
       photograph (by the way, the lotus at the bottom is not there when
       they took the photo, in case you are wondering…)

Some exceptional practitioners such as Padmasambhava are held to have realized a higher type of rainbow body without dying. Having completed the four visions before death,His or her physical body self-liberates into a nonmaterial body of light with the ability to exist and abide wherever and whenever as pointed by one's compassion.

       TheNON2: Supernatural Energy