This night I've seen two SL-16 R/B on the sky with my binoculars. These where part of some Zenit rockets that launched satellites in the 90s. They travel at altitudes that double the ISS, uncontrolled.
I tried to understand what part of the Zenit rocket are they exactly but I couldn't find an answer. I guess they are not the first stage since that shouldn't get to orbit, is it then the second stage?
My questions are:
1) What part of the Zenit rockets are they?
2) Is there any model or picture to see how they look?
3) What size does it have?
4) How long is expected for these objects to be in orbit? One of those I saw this night was there since 1995 so I guess there is little drag at that altitude.