A mere 25,724,800 miles away, Venus is Earth’s closest planetary neighbor. Often called Earth’s “sister planet,” it’s similar to our homeworld in many ways: their diameters, mass, volume, and even gravity are roughly the same. Early science fiction writers used to imagine Venus as a hotter, junglier, more mysterious version of Earth, populated by evil aliens and alluring vixens in equal measure.
Those old-timey sci-fi cats were, of course, super wrong about all but one thing: Venus is hotter than Earth—over 800°F hotter. To help students understand why it’s so much toastier on Venus, your friends at Demo Science cooked up this easy cheesy lemon squeezy science demo.
Build A Jaromometer!
Round up two thermometers and a jar big enough to hold one of those thermometers, and you’re good to go. It should be noted that the thermometers must be the old, classic-looking glass tube kind, or this experiment will not work (I swear) and your students will think you a buffoon.
The execution is almost comically simple: put one of your thermometers in the jar and secure the lid tightly. Put your both the jarred thermometer and the non-jarred thermometer by a window with direct sunlight streaming through it. Get a game of Heads Up Seven Up going for twenty minutes or so, then go back and check on the thermometers.
What you (and, more importantly, your students) will find is that the jarred thermometer will show a significantly higher temperature than the free range thermometer. But why?
Mostly Entirely About Atmosphere (Mostly)
The sun’s radiation contains both visible light (obviously) and invisible (to humans) infrared light. Most extremely hot things, like our sun, which runs at a balmy 27,000,000°F or so, give off infrared light. But both thermometers are in the sun, so that’s a wash.
What really gooses the reading on the thermometer-in-a-jar is the “in-a-jar” part. In this experiment, the jar mimics the Venusian atmosphere. Venus’ atmosphere is very thick compared to Earth’s, and while the sun’s visible light hits Venus like it does any other planet in our solar system, the atmosphere blocks most of it, allowing only the “hot” infrared light to reach the planet’s surface. The thick atmosphere traps the infrared energy and keeps it from escaping, which, in turn, makes the planet hotter still.
Your jar, of course, does not block the visible light, but it does trap a good deal of the heat. With nowhere for the heat to disperse to, the inside of the jar heated up, giving the enclosed thermometer a higher reading.