If there are alien spaceships with cloaking device observing us within Earth's orbit, how can we detect them?

We can’t Padawan. They’re cloaking themselves from us.

waits patiently for the sound of blowing minds . . .

By becoming worth talking to and asking.

@talljasperman Indeed. Indeed…

Heat emissions.
There are quite a lot UFO sightings that were only visible in infrared.

We need a fleet of spaceships that fly around looking for anomalies… like suspicious missing patches of stars through the windscreen. These ships should then aim a cannon load of vaseline at the anomalous area, followed immediately by a blast of talcum powder. Voila! spy revealed.

@Blondesjon What about a sonar like device that we could attach to all the future satellites we will launch and use it to ping at their hulls with? : )

@Blueroses We better recruit Austin Powers to lead this mission then. Lol.

@mazingerz88
Sonar uses sound. There is no medium in space to carry sound waves.

Interferoscopic magnetons. Shhh. You didn’t hear it here!

@ragingloli Thanks, yes! Shows there is no way I could ever write a Star Trek script. Lol. So, what’s in a vacuum that we could detect, observe and measure in order to discover anomalies that may turn out to be ships out there? Wobbling light?

I say we some make really, really, really long sticks and wave them around in space until we hit one of them.

@lillycoyote Best solution ever!

You’ll never catch us unless you use @lillycoyote‘s solution… and put some tasty melted marshmallows on the ends of them.

@Symbeline I was catching up on Survivor last night and on the episode I watched they had the two people on Redemption Island fashion really long sticks to get keys off a hook. If I hadn’t watched that, I never would have thought of that solution. And people say nothing good can come from watching reality television! :-)

@RealEyesRealizeRealLies Aliens! Marshmallows? You are nothing but orbiting pinatas to us!

I see them all the time. It’s rather simple you just {redacted}

@zensky you just go where no man has gone before! :D

Maybe they will collide with some of the space junk in orbit.

look for a disturbance in the force

use the instruments we use for cataloging gases, after all the thing has to have a tailpipe…

Flash ‘em. They’ll show up themselves.

Hey – @Ayesha – settle down girl. You’re underage in space, too.

Pigeons!
They’d quickly develop headaches from constantly bashing their bonces off these craft.
Disheartened by this violation of their airspace, they’d approach local farmers/rednecks, cooing & frantically pointing one wing to the skies, while tapping the side of their heads with the other.

@ucme Just to clarify, astronaut pigeons, right? With the cute space helmets? : )

@mazingerz88 Nah, these pigeons can hold their breath a really long time.
Space pigeons, imagine all that shit on the windshield of those alien ships.

All mass has an effect on its surroundings, so even a cloaked spaceship would have an effect. it would have a transit effect across the sun for one thing (which is how we detect extrasolar planets).

Actually though, my answer is that we would detect them by throwing slices of cheese pizza at them and watcing it bounce off. (I’m working on a game of this nature called “The Pizza of Death”)