There is now a new article called How Time Works that answers all of these questions about clocks and calendars, plus many more! You will be amazed, because we take all of this stuff completely for granted and the origins are amazing!
High material costs and relatively low efficiency have held solar energy back as an alternative to fossil fuels. But that hasn't stopped people from finding some practical everyday applications for solar panels.
How many regular-sized helium-filled balloons would it take to lift someone? What is the equation to figure it out?