Is translating an article (that could be found written in a popular science magazine or online in a science blog or personal webpage say) for a public newspaper or an online blog ...etc, requires permission from the author?
If the article you wish to publish is not in the public domain or under a license that allows preparation of derivative work, you must get permission from the copyright holder to translate it. (Unless one of the copyright exceptions applies.)
Besides the very good answer given by ff524 it's noteworthy that national laws apply and that those differ significantly. No matter what - it's always a good idea to get permission from the copyright holder (most likely the author or the publisher).
To give an example. German copyright law states the copyright as non transferable. So no matter how much the publisher would like to they cannot get the copyright from the author. However the publisher is usually granted an exclusive right of publication (at least for a limited amount of time). This license agreement between copyright holder and publisher might contain a clause concerning translations. So again the request for permission is necessary.