It is a push, but the scientific plausibility can be obtained. For example, six suns surround a planet, and change positions randomly every day. This would imply that the biological clocks of the alien world inhabitants must run really slow - compared to our clocks - so that the suns have the apparent speed of relative motion across the skies. Hard to see how the system could be stable, though, with a planet which skips about between the suns.
Off-putting is the fact that the population keep talking about the suns and darkness. As on Earth, the suns would just be taken completely for granted, and darkness, which noone has ever experienceed, would not have a word to describe it - then again, surely someone would have experimented with darkness? Surely it wouldn't be such a foreign phenomenon as it is made out?
There are also some unrealistic inferences made about the nature of stars. These have never been experienced, but people guess at what they must be like with an accuracy that can only be achieved with hindsight (except there is one deliberately wrong guess thrown into the story).
It is hard to see how the book could otherwise have been written, however.
The crux of the story is that when the last of six suns is eclipsed and the world is plunged into darkness for the first time in 2049 years, the stars appear and cause madness amongst the people. I can't help feeling that this is unnecessary, and that the darkness alone could have accounted for the rampant madness that ensued. Furthemore, the world is described as one having a climate like ours, with clouds and rain. But this would have meant that the people in some parts of the world would not have seen the stars, and so the continuity of civilization would have been unabated there, in contrast to the ideas in the beginning of the book indicating complete downfalls of all previous cultures.
This is a book which, like the films Titanic and Star Wars III, you basically know the plot from the minute you pick the book up. This gives it the tedious pre-tension of a horror novel, and leaves the reader constantly (and usually correctly) predicting the next few pages (I really don't like horror novels).
All in all, it is a good book, well thought through, and, at a small stretch, plausible. The last thing that I find personally not right is that in the end (the implication is) the university people give power back to the religious crackpots who take the responsibility for maintaining continuity in the civilization. I can't help thinking that intelligence would win out in the end.