Whilst in Germanic mythology *Thunaraz became eclipsed by the increasingly more dominant *Wodanaz, in the Balto-Slavic world His equivalent maintained His dominance, although He was not always the most prominent deity in their pantheons:
"We will now examine it a little more in detail, commencing with the ideas attached to the early inhabitants of Russia to those solar gods who are supposed by many eminent scholars to have originally held higher rank than the wielder of the Thunderbolt, Perun." (Songs of the Russian People, William Shedden Ralston, 1872)
Readers of my blogs will realise that I have maintained consistently that over the millenia there has been a shift of power from *Tiwaz to *Thunaraz and then to *Wodanaz which is mirrored in the Celtic mythology also or at least the transfer of power from Nuada to Lug is. Taranis does not appear to be so prominent as *Thunaraz at the time of the recording of the Irish myths. The primary divine archetype that the folk requires does change from era to era to meet their current needs. We see a similar thing happening today with the gradual eclipse of the Woden archetype by Widar, His son.
Referring to the early solar deities of the Slavs Ralston states:
"The most ancient among these deities is said to have been Svarog, apparently the Slavonic counterpart of the Vedic Varuna and the Hellenic Ouranos. His name is deduced by Russian philologists from a root corresponding with the Sanskrit Sur-to shine, and is compared by some of them with the Vedic Svar, and the later word Svarga, heaven."
The Sun is the child of Svarog and is called Dazhbog. Dazh is identical with the Germanic Dag which in modern German is Tag, day. Thus Dazhbog is the Day God. Bog of course means God. Another son of Svarog is Ogon, fire and is cognate with the Indian Agni, which is where we get the modern English ignite from. As mentioned in my recent article http://aryan-myth-and-metahistory.blogspot.co.uk/2014/10/parjanya-original-indra-and-cognate-to.html the Indian Thunder God Parjanya is a more ancient God than Indra and performs very similar functions but appears to be less war-like. Clearly Parjanya is etymologically linked with Perun and Perkunas, being derived from the ancient Proto-Indo-European *perkunwos.
"Russian mythologists identify the name of Perun with that of the Vedic Parjanya. Whether the latter was an independent deity, or whether his name was merely an epithet of Indra, does not appear to be certain, nor are philologists agreed as to whether Parjanya means 'the rain' or 'the thunderer;' but 'it is very probable that our ancestors adored, previously to the separation of the Aryan race, a god called Parjana, or Pargana, the personification of the thundering cloud, whom they believed to rouse the thunder-storm, to be armed with the lightning, to send the rain, to be the procreator of plants, and the upholder of justice. Afterwards the Graeco-Italian nation, bent on the adoration of Dyaus, forgot him entirely; the Aryans of India and the Teutonic tribes continued to worship him as a subordinate member of the family of the gods, but the Letto-Slavonians raised him to the dignity of a supreme leader of all other deities." (Ralston)
The description of Parjanya, more so perhaps than Indra corresponds more closely to the Balto-Slavic Thunder God:
"The desription of Parjanya is in all respects applicable to the deity worshipped by the different branches of the Slavo-Lettic family under various names, such as Lithuanian Perkunas, the Lettish Perkons, the Old Prussian Perkunos, the Polish Piorun, the Bohemian Peraun, and the Russian Perun." (Ralston)
"Vayu-or Vata- 'Wind' is properly of atmospheric origin, a gale-god whose Indo-Iranian age is proved by his more important Iranian counterpart Vayu. Parjanya-(once [RV 1,164.51] in the plural [cf. Rudrah] is a related rain-god figure cognate in name with the Baltic (Lithuanian) thunder-god Perkunas and his Slavic (Old Russian) counterpart Perunu; in that case he is an ancient variant of the type, shunted to the Vedic periphery by the ascendancy of Indra." ( Comparative Mythology, 1987, Jaan Puhvel)
The Balts and Slavs lit a sacred fire before the image of the Thunder God:
"In Lithuania Perkunas, as the God of Thunder, was worshipped with great reverence. His statue is said to have held in its hand 'a precious stone like fire,' shaped in the image of the lightning,' and before it constantly burnt an oak-wood fire. If the fire by any chance went out, it was rekindled by means of sparks struck from the stone. His name is not yet forgotten by the people, who say, when the thunder rolls, Perkuns grumena, and who still sing dainos in which he is mentioned. In one of those a girl who is mourning for the loss of her flowers is asked,-
"Did the north wind blow,
Or did Perkunas thunder or send greetings?
In another it is told how when
The Morning Star held a wedding-feast,
Perkunas rode through the doorway,
Struck down the green oak" (Ralston)
There are many more such dainos or heathen hymns preserved by the Lithuanians which refer to Perkunas. It would serve us well to study them in more detail.
According to Jaan Puhvel the Goddess Frigg's father or lover was called Fjorgynn. Also a Fjorgyn is named as the mother of Thor. This is possibly an alternative name for Jord (Earth). These names Fjorgynn and Fyorgyn are cognate with Perkunas and they in fact have been a divine couple.
The German language Prussian Chronicle from about the year 1520 refers to the worship of a divine triad of Patollo, Potrimpo and Perkuno by a high priest called Bruteno. The icons of the Gods were installed in three niches of an oak tree. A perpetual fire was burned before the icon. As Lithuanian heathenism was not abolished until as late as the 15th century and it still continued to linger on it would serve us well as Germanic heathens to study closely the Baltic myths to gain greater insight into our own closely related Germanic deities. It should be noted that heathenism is growing in the Baltic and Slavic lands at an apparently faster rate than in Germanic countries.