In Public Service Broadcasting's video for their song "Sputnik", there's some very nice animation of the first manmade satellite orbiting the Earth. Sputnik is shown to be polished to a mirror finish. While this makes for dramatic imagery, it seems less than plausible to me for reasons I can't put my finger on.
So just how shiny was Sputnik, anyway?
The Sputnik-1 was indeed just as shiny as you see in replicas and media. In fact, it was a key design feature. Apart from tracking by radio, it was intended to be visible to ground based observers. It doesn't take a very large object to reflect enough sunlight to be visible in the night sky. You can sometimes see streaks of light in the night which are actually just sunlight-reflections off satellites, such an occurrence is known as an iridium flare. Though it must be said that today, ground based visual observation isn't a feature of satellites, instead, it's a result of the various reflective materials used for insulation and/or solar arrays.
Source: https://nssdc.gsfc.nasa.gov/nmc/masterCatalog.do?sc=1957-001B
If you want to try to observe an iridium/satellite flare, check this article out for details: http://www.skyandtelescope.com/observing/celestial-objects-to-watch/observing-iridium-flares/