Autonemesis

Yes, that's called Olber's Paradox, even though he was not the first to pose it: "Why is the sky dark at night?"

If the universe is static, uniform, infinite and eternal, as was generally assumed in the 17th century, then the night sky should be ablaze with light as bright as the sun since every direction you looked, your line of sight would sooner or later intersect the surface of a star. But the night sky is dark, therefore at least one of the assumptions had to be wrong, and so cosmology became one of the observational sciences, not just theoretical.

eh

Yeah, the funny thing is, I live in a steel town. I couldn't understand what the hell people were talking about when they mentioned a dark night sky. As far as I was concerned, the night sky IS glowing. A visit to the countryside cleared that up for me.

B. H. Manners

Why are we able to pick up sun size stars in other galaxies but cannot pick up planets around other stars in our own that are twice the size of jupiter?

Shadowy Man

yes.

do you know how difficult it is to see planets? stars are very, very bright.

NonHomogenized

Well, let's look at the objects involved:

Sun-like Star: A giant ball of thermonuclear reactions (a bit oversimplified, I realize, but, good enough for this purpose) which radiates approximately 4*10^26 joules per second (watts).

Planet: A large ball composed of various elements. Reflects light, but does not produce any (Jupiter has a luminosity of about 4*10^17 watts, or 1 one-billionth that of the sun, and a larger portion of it is not in the visible spectrum than the energy output of the sun).

So, if we could see a jupiter-like planet orbiting the nearest star, alpha centauri (4.3 light-years away), we'd be able to see a star like the sun at least (in our simplistic model, anyhow) 4.3 billion light-years away.

So, why can't we? Easy: we don't see planets outside the solar system at all. We detect them by the fluctuations they produce in the light of the star they orbit. If they're not signifigantly larger than Jupiter, we cannot at present reliably detect/analyze said fluctuations.

Shake

IIRC, all of the observeable (not necessarily visible, mind you) matter in the Universe makes up something on the order of only 10% of what current theory predicts. I.e. roughly 90% of the matter in the Universe is comprised of so-called dark matter. Possibly less if neutrinos are found to actually have some mass (something I've read a little bit about lately).

Of course, I'm just a semi-well-read layperson. You'd have to look up the particulars.

Lobstrosity

We do not possess at this time the ability to optically resolve a planet from its star at this time. The star is vastly more luminous than its companion and it's profile is a spread-out Gaussian surrounded by defraction rings produced by the telescope. This lack of resolution means that the planet's presences is optically masked by the star about which it orbits. New technology in the works may actually possess the resolution to directly observe what are known as "hot jupiters." One is the Keck interferometer. Currently, the twin Keck telescopes are the largest optical and infrared telescopes in the world, each having a diameter of ten meters. A project is now under way, however, to interferometrically link these two telescopes to produce, in theory, the resolving power of a 100-meter telescope (the baseline between the two is approximately 80 meters.

http://planetquest.jpl.nasa.gov/Keck/direct_detect.html
http://planetquest.jpl.nasa.gov/Keck/keck_index.html


The Space Interferometry Mission also would be able to directly resolve planets around other stars. It would be more effective than Keck because it won't have to deal with atmospheric distortion (which makes interferometry quite difficult due to asymmetric distortion of the wavefronts one is trying to combine).

http://planetquest.jpl.nasa.gov/SIM/sim_index.html


In short, if you want to be able to see planets directly, you need much more resolving power than any current telescopes have. Interferometry appears to be the way we'll eventually get there.