If they said "blue," we could investigate why the sky is blue, talk about what light is, debate particles vs. waves, investigate the electromagnetic spectrum, study rainbows, Raleigh scattering, sunsets, transparency vs. absorption, sunburns, radio/tv/cell phone signals, and anything else they want to find out from there.
If they said "clouds," we could investigate what clouds are, the water cycle, why and how liquids condense and freeze, why hot air rises and rain falls or doesn't, what lightning and tornadoes and hurricanes are. Maybe then we'd be fascinated by disasters and investigate earthquakes and the structure of the inside of the Earth and other planets. Or maybe we'd decide to look more closely at electricity and build our own charge collectors and study Coulomb's Law and from there move to capacitors and circuits and then wave a compass near a strong current and build a motor.
If they said "birds" or "trees," we could investigate which particular birds or trees or other living things live where we are, how they've adapted to living here, how other living things have adapted to living elsewhere, what living things need in their environment, what we would need if we wanted to export ourselves to another planet, what makes a planet habitable for creatures like the ones around us, the search for other habitable or inhabited planets, the scale of the solar system and the scale of the galaxy, the Drake equation and how to talk about stuff you don't know.
If they said "stars" or "the Moon" or "the Sun," we could jump directly into the structure and behavior of the solar system, what holds it together, how we know what we know about the solar system, maybe we'd build a telescope or maybe we'd look at Hubble photographs with Galaxy Zoo or hunt for craters on the Moon. We would definitely have to keep a Moon journal, argue about whether Pluto and Eris and Ceres and Makemake should be planets or not, talk about eclipses and transits and eclipsing binary stars and searching for extrasolar planets, and wrestle with how light be both a particle and a wave at once while going so awesomely fast that time stands still.
I wouldn't be able to write a content-based final exam for the class before June, but I could write an open-notes, process-based final exam:
- Explain the scientific process, using examples from your work this year.
What question(s) would you use to start a class?