Sun has been revered across cultures since time immemorial. Ancient Egyptian God of Creation, Amun resided in the Sun and from 4th Dynasty Sun was worshipped as deity Re. Aztecs knew this energy as Tonatiuh, Pre Islamic Arabia worshipped it as Shams/Shamsun, Baltics as Saule. The Sun God occupied a central position in both Sumerian and Akkadian religion as Utu and Shamash. In ancient Rome, feast of Sol Invictus (Unconquered Sun) on December 25 was celebrated and eventually this date was taken over by the Christians as Christmas. Surya is glorified in the Vedas as the devta of gyan, who rides a chariot of seven horses, which are the seven colours of spectrum as observed when sun rays pass through a prism.
What is in the sun that renders it so special and auspicious? It is the heat of the sun. Science tells us that the temperature at the surface of sun is about 5,600 degree Celsius and that at its core is over 15 million degree Celsius! Compare it to the temperature on earth. On a hot summer day if the temperature even nears a 50 degree Celsius, we get uncomfortable and are unable to bear it. Imagine what it would be like to near the sun? If earth was to approach the sun, it will burn out in mere 10 per ecnt of the distance! That is, the earth and its inhabitants do not have the capacity to take the heat of sun.
The heat of sun is the heat of gyan. To access gyan, to go near the sun, one needs to increase the capacity to withstand this heat of gyan. That is, one has to constantly increase his/her heat, in other words tapa, through seva and sadhna under a Guru. There is no time to pause or rest, because the temperature difference is phenomenal.
Everybody wants gyan, but how many are prepared to bear the heat? This becomes the deciding factor for those who stay on the path and those who leave… because majority will run to seek comfort in an AC room at the slightest exposure to heat. Heat here refers to the strife which is a constant in the journey of a sadhak. That heat has to be generated. And that heat is also not for the self, it is to redistribute in Creation. The day sun decides to hold the heat with itself, that day the sun will disintegrate. So one generates that heat and then distributes it, as an equal and opposite reaction the heat of the person increases manifold.
People who are adept, when they perform a yagya (you can see the video on Dhyan Foundation website) they are able to keep their hand in the yagya agni without any blisters or the hand burning. If you increase the heat inside you through right practices under a Guru, it will happen with you too.