A story about a derelict ship orbiting a planet with spider-like creatures

I read this one probably about 15 years ago, but it was already somewhat older then. I would put it in the 1980s maybe?

There are some details I remember, but the thing I remember most is the meeting at the end, and it's a thing I've wanted to share with people a few times already... if only I could remember the title of the book.

From what I remember:

• There is a planet which is sometimes warm and light, and sometimes goes into a dark, cold state (when it moves too far from the sun I think?).


• Two factions of humans have a spacewar near the planet, which ends with both factions crippled.


• Unknown to them, it turns out spider-like alien creatures live on the planet below. They hibernate during the cold periods and live during the warm ones. Throughout the book their society and civilization advances quite a bit.


• One of the aliens sees "strange flashes of light", which is the battle happening overhead. He is one of the main drivers of progress on the alien planet if I remember well.


• For most of the story, these aliens and the main characters on the derelict ship live separately, but at some point they start communicating.


• When they communicate, it very much feels like two vaguely-humanoid species talking.


• At the end of the book, the aliens rescue the main characters on the derelict from the bad guys (who are also there, I think the MCs were prisoners or something?)


• And then they meet; and in that meeting it completely changes the way the aliens are described and you suddenly realize you've been subconsciously treating these completely alien things like humanoids and how weird that was (or at least; that's what it was like for me).

I hope someone can tell me the title of this book, so I can share how cool it is with more people.

Answer

This is A Deepness in the Sky by Vernor Vinge (1999), the prequel to A Fire Upon the Deep.

The plot begins with the discovery of an intelligent alien species on a planet orbiting an anomalous star, dubbed OnOff because for 215 of every 250 years it is dormant, releasing almost no energy. During this period, the planet freezes and its fauna go into hibernation. The planet's inhabitants, called "Spiders" by the humans for their resemblance to arachnids, have reached a stage of technological development very similar to that of Earth's humans in the early 20th century, although humans believe that they may once have been capable of space travel. If this is true, then whoever can establish ties with the aliens first could reap unimaginable rewards.