2 ms·

Doesn’t this ignore the vast number of systems between us and the visible star?

• lrem 5y ago
  It doesn't. Imagine the night sky. What do you see? I see stars, that are bright dots on black background. That is, to a first approximation the overwhelming fraction of the area of the sky actually doesn't actually have a star. Now, the obvious error in that is the Milky Way, which is kind of a faint bright smudge. The non obvious error is that some things I see as stars really aren't. In both cases you can get a telescope and see that, upon closer inspection, this is actually a bunch of stars on black background, that were close enough to seem to be one star, or a smudge. As you point ever stronger telescopes at those, you discover that many smudges and stars are in fact bunch of individual stars (but some stars are actually singular stars and some smudges are nebulas). More annoyingly, when you point those telescopes at the black background, you notice more individual stars on black background. Now, you'd think you know the pattern and can do it ad infinitum. But you can't, because at some point the black background is resolved to the point of, well, the background radiation at the edge of the visible universe. And some of the bright dots turn out to be dense clusters and galaxy cores, where we can't make out individual stars. But, as far as I understood, we have catalogued tens of millions of stars we have a clear view of. And when something passes between our system and a visible star, it's often (usually?) an exoplanet in that star's system, of which we've discovered almost five thousand.