All OK, except the second line: 'presence in Bulgaria's [no N] skies'. "Sky" would be OK, but I think the plural would sound better.
"On the occasion of" doesn't sound very warm, but it's OK; I'd prefer something like 'Celebrating' or 'In celebration of' or 'To celebrate'. Or even, maybe, 'Marking' - but that sounds a bit cold too.
Student or Learner