In EVE everything within 1000km is on the same "grid". within a solar system you can only warp to known locations. That includes locations that were manually saved or celestial objects like moons and planets.
That means when someone warps to a moon, they can see anyone who warped to that moon, since they are on the same grid.
A safe spot is a location that isn't on the same grid as a known location. You can still be scanned down by someone, but there are ways to know about it.
Edit: Its been a while and I'm no expert, so anyone feel free to correct me.
Mensch, nach dem "Abrutschen" muss der Fuß aber mit der Schwerkraft vom 1000 Sonnen auf dem Pedal festgesteckt haben, damit man so lange auf dem Gas bleibt