the English sentence is in past tense.

Yes, I was aware of that, but I adapted it to the grammar of Esperanto.

I believed that in English they wished to say that during that time (when they believed), he was the son of the sun. In Esperanto you don't have to retain the past tense; instead, you can use the present tense, thus informing the reader that this fact is relevant for the present (even if that present was the past in the sentence).

So, the present tense was intentional in my sentence. However, this is still debatable, of course.

I was about to suggest that I would post another variant, in the past tense, when I realized that I have already done that. In fact, I took into consideration both scenarios, and posted one sentence for each :)

>So, the present tense was intentional in my sentence. However, >this is still debatable, of course.
I can't agree with you in the last point, because it's NOT debatable. In my comment I'll try to use a simple kind of Esperanto, so that - as I hope - it won't be to difficult for Marcello to understand. (By the way, Marcello, meanwhile I've seen some of the sentences you have produced recently, and I'm really impressed. You've made very fast progress in Esperanto).

La klarigo estas tre simpla.
La angla lingvo kaj Esperanto estas du apartaj mondoj kaj inter ili estas multaj diferencoj.
Pri tio ni povas facile konsenti, ĉu ne?

Unu el tiuj diferencoj estas la rilato inter rekta parolo (direct speech) and nerekta parolo (reported speech).
Se vi prenas anglan frazon en rekta parolo kaj volas transformi ĝin en nerektan parolon, tiam povas okazi, ke vi devas ŝanĝi la tempon de la verbo (pardonu se mi mencias tion, vi certe scias tion).
SED NUN: JEN BONA NOVAĴO!
Se vi transformas esperantlingvan frazon el rekta en nerektan parolon, tiam VI NE ŜANĜAS VERBOTEMPOJN.
Jes iam la vivo povas esti vere facila!!!

En la supra frazo "ili" ne PAROLAS. Ili pensas. Sed tio (gramatike) ne faras diferencon. Validas la samaj principoj:

English
Direct speech: They thought: "He is the son of the Sun."
Reported speech: They thought he was the son of the Sun.

Esperanto
Rekta parolo: Ili pensis: "Li estas la filo de la suno"
Nerekta parole: Ili pensis, ke li estas la filo de la suno.

Mi esperas, ke tio ne estis tro malfacila klarigo, sed demandoj estas bonvenaj.

Marcelo, actually, as I wrote my comment during the night, I saw that I had already added the other variant:

http://tatoeba.org/eng/sentences/show/686168
Ili pensis, ke li estis la filo de la suno.

in December 2010, more than a year ago, when I posted my current sentence.

Now, however, the other variant seems wrong, as the English should have been:
They thought he *had been* the son of the Sun.

and only then the correct variant in Esperanto would have been:
Ili pensis, ke li estis la filo de la suno.

I won't delete my other variant at the moment, but wait to hear your opinion, Alex and Marcelo. I believe we should delete the other variant, though, as it now seems to me incorrect (after I have reconsidered it).

@Eldad
>"...the English should have been:
>They thought he *had been* the son of the Sun.
>and only then the correct variant in Esperanto would have been:
>Ili pensis, ke li estis la filo de la suno."

You are completely right.

Excellent, so I'm deleting my other variant.
Thanks.

Venontfoje, mi simple malligos... :)
Mi forstrekis la frazon, sen kontroli ĉu alia frazo estas ligita al ĝi. Nu, oni lernas...

Very interesting. : O