Since the universe we live in is so complex, science has a pretty hard job. Because it has to try and give explanations for all the phenomena in this great universe in an orderly, rational, provable fashion. And since everything is connected to everything in the universe, from the macroscopic level to the microscopic one, and our human mind tends to work by dividing things and putting them into neat categories, you can see why mistakes may happen.
Not necessarily because a certain scientific theory is flat out wrong, although that sometimes happens as well, but because the information available at one point changes later and influences the premises that the theory was initially based on, which needs to be revised.
However, when that theory is revised, the world and its people who aren't scientists don't necessarily follow suit. Which leads to cases in which a certain thing is believed which might seem plausible or might have seemed so in the past, but is no longer so.
Since space is vast and its field of study is equally so, here's 3 space things people know wrong. Keep in mind that the things discussed below might suffer revisions as well, if new information comes to light.
1. The emptiness of space
I'm sure you've heard this expression frequently in sci-fi movies, usually with the accompanying intense stare into nothingness of a main character, along with dramatic music. Well, scientists are now saying, based on recent discoveries that space might not be all that empty after all. And that even between planets and stars, though there is a seeming void, in fact there the density of material is just really really low, but clearly not zero.
Not to mention that even more recent explorations focus on something called dark energy which seems to be is everywhere within that void and all around the universe. Though some theories explain it as being part of the fabric of space and others use different approaches, it is still an argument that the space between planets and stars is not just nothingness.
Explosions and the fires that accompany them do not behave at all like we've been taught in the movies. Meaning that a great wave of fire, sound and accompanying shock-wave do not happen. This is logical if you come to think about it. As fire needs oxygen to burn and sound is actually pressure on your ear-drum caused by moving masses of… air, water whatever as long as it is liable to cause vibrations.
But keep in mind that there would be oxygen at hand, from inside the destroyed vessel. So in fact, an explosion in space would happen, but it would take a fraction of a second while the fire manages to consume some of the oxygen before it dissipates and it would look kind of like a flash.
3. Dodge skills
You won't need that much of them. In case you thought they were essential when navigating an asteroid field. Which is another common opinion often depicted in movies. You know, that part when the beleaguered protagonists, the underdogs and their clearly inferior ship in size and firepower decides to take the dangerous decision of losing the other ship in an apparently suicidal attempt to traverse a dense asteroid field.
In reality, asteroid fields's elements are pretty widely spaced apart. Along the lines of weeks, months or even years of space travel between one asteroid or another, with current technology. Which is something that some legendary sci-fi writers knew very well and made note of in their works (like Orson Scott Card in his prequels to “Ender's game”, which features a family of asteroid miners).