When looking at the night sky, the stars we can see just look like single dots. Are they alone in space- each one a single object? Or, when we look at a star, are we actually looking at a distant solar system within our galaxy?
What we see from the Earth's surface with our eyes are just stars, any planets surrounding them - indeed, entire planetary systems are not visible by the naked eye.
That does not mean that there aren't any planets around those stars, the exoplanets listed in this European based Exoplanet catalogue were detected using much more precise and sophisticated means, listed on NASA's Years of Exoplanets page as:
- Doppler shift measurements
- Astrometric measurements
- Transit method
- Direct observation
- Gravitational Microlensing
The NASA page also describes why it is not possible to tell if a star has planets from observing with the naked eye:
The challenges of observing extrasolar planets stem from three basic facts:
- Planets don't produce any light of their own, except when young.
- They are an enormous distance from us.
- They are lost in the blinding glare of their parent stars.
Asides from stars, looking up with the naked eye, we may also be looking at galaxies, systems of stars etc. - these would be resolved using instruments, not really discernable with the naked eye.