Hi Slava
In general, I agree with Ivan's answer (above), but just to add that "celebrate" is more often used for happy events, whereas sometimes "mark" means to 'recognise the importance of'' an occasion.
For example: "Next year it will be 10 years since the terrible loss of life in the earthquake , and authorities are already planning to mark the occasion." - "celebrate" is not quite the right word in this context
Hope this helps
Chris