Sherlock Holmes and Dr. Watson were on a camping expedition. One night, Holmes wakes Watson and says "Watson, look at the stars above us, and tell me what you deduce."
Watson, rising to the challenge, says "Well, I notice that the stars shine brightly, which tells me we are far from manmade light sources, i.e. cities. They twinkle very little, so I know that we are viewing them through a relatively thin layer of air, i.e. we are at great altitude."
"Judging by the visible constellations, we are in the Nothern Hemisphere, and the declination of these constellations tells me that morning is fast approaching."
Watson winked and added "Oh, and I can guess by your question that Astronomy is one of your hobbies".
Holmes raises an eyebrow, and says
"Watson, you idiot. Someone stole our tent!"
