Originally Posted by chaika
No, that's not right.
The letter O can also be pronounced as a schwa, the dreaded uh-sound (I use # to indicate this sound). In standard Russian, as I understand it the rule is
words spelled with letter O in pretonic syllable: the O is pronounced A. For example, Mосква is pronounced /maskva/.
But if an "o" occurs in earlier pretonic (tonic syllable = stressed syllable) positions, or in post-tonic positions, it is pronounced like the a in English sofa. At least when I say it, it's not "sofA" but "sofuh". This uh-sound is called schwa.
So take the word города cities. The first O is pronounced uh and the second is ah [guhradA]. And look at новости [nov#s't'i].
And I'll tell ya this, it's even more complicated, but you won't be wrong to pronounce any unstressed letter O as /a/. дАстАпримечательнАсти will sound a little unusual to a Russian but probably better than дОстОпримечательнОсти, which will make you sound like a real peasant out of the North!