* Size and Reflecting Surface: Sputnik 2 was much larger than Sputnik 1, but it was also more complex with a biological payload, which meant it had a smaller reflective surface. This made it harder for the human eye to detect.
* Orbital Trajectory: Sputnik 2's orbit was slightly different from Sputnik 1, with a higher perigee (closest point to Earth). This placed it further away from the surface, making it dimmer.
* Brightness: Sputnik 2, like Sputnik 1, relied on reflecting sunlight for visibility. It was not equipped with any lights.
Therefore, while it was theoretically possible to spot Sputnik 2, it required ideal conditions (clear skies, dark surroundings) and sharp eyesight. It was not as bright or easily recognizable as Sputnik 1, which was a major news event.
