I'm doing my MS in Astronomy and Astrophysics so almost all of the literature I need is readily available on NASA ADS website (ui.adsabs.harvard.edu) with links to downloadable PDFs and HTML articles. But sometimes I come across conference proceedings, or some old articles where only abstract is available for reading but it DOES contain what I'm looking for.
Since I can't read the whole thing, is it okay to cite that?
Apart from the original links to downloadable PDFs, if something I want to cite is in the abstract but I want to dig deeper and the paper is not available for download in any form, should I look for other papers that have same information and are available or can I use sci-hub. And how fair is it to use sci-hub?