Several times each year, Stroller Hikes participates in huge community events, such as festivals and fairs. This coming weekend, on Saturday, September 21st, Stroller Hikes will participate for the 7th time at the 8th Annual Blossom Family Picnic, more recently named Birth and Family Fair (BFF). This year, Mora, Blossom’s director, invited us to do something more science-y than our usual obstacle course, tattoos, or crafts.
I asked Max what we should do, and he of course arrived at what he enjoys most about hikes – plants and animals to discover along the way. We’ve had a “touch tank” before with slugs and snails, pill bugs and caterpillars, but with probably over two hundred people interacting with them throughout the day, I would feel guilty for imposing so much stress on the critters. So animals are out. What to do with plants?
It had to be hands-on. It had to be intuitive. It had to be interesting and relevant to the whole family…
What’s more all-encompassing, important, and relevant than the sun? Many of us slather on sunscreen daily, look to the skies to decide what to wear for the day, and love plants for their shade, color, and smell. And with renewed interest in sustainable forms of energy, solar power can be thought of as more than just a feature of weather.
So if you come out next weekend to see the Stroller Hikes booth in downtown Palo Alto at BFF, here’s what you’ll find us doing: Making UV-sensitive bracelets (beads change color in the sun), cooking up some s’mores in a simple solar cooker, and exploring what colors are best to wear on sunny days that are hot (answer: white) or cold (answer: black). This all lends itself to how plants have made use of solar energy over the ages, but let me first explain the science behind color, heat, and the sun.
Energy comes in all forms, including sound, light, heat, and movement. When energy hits molecules, molecules often change, and the energy changes as well. We often quantify the amount of energy based on temperature, because thermometers are so easy to use. When light hits pigment molecules, it can reflect off of them, or enter the inside of the molecule and bounce around a bit, perhaps being bent or split into different types of light, or changing to heat energy. A prism (typically cut glass) has all sorts of angles to it, so light will hit a flat surface and bounce off, helping us see that surface as shiny. At an angle, light can separate into several colors, and we see a rainbow. Something similar happens with large molecules like proteins. Proteins are so big and complicated in terms of shape, they are not so different from a prism with holes here and there, and sides that are not always flat. When light hits the protein, the light can not only reflect and separate, but can enter the nooks and crannies of space in the protein. Based on this movement of light, the protein will appear to be a certain color and sheen. If light becomes trapped, its absorbance into the pigments are detected as heat.
Unique proteins present different colors, based on their own obstacle courses along which light can travel, bend, and break. This is why your black shirt is black, your blue shirt is blue, and your white shirt is white. Black pigment is shaped so light’s obstacle course has enough space for light to enter, split, and be trapped. That’s why a black t-shirt will get warm on a sunny day, relative to a white shirt. White pigment is more reflective (imagine a prism with a largely flat surface and less nooks and crannies), so the light reflects off of it pretty quickly. On a cool day, black is better to wear than white (for keeping you warmer), but white is a great choice when it’s sunny and the air temperature is already plenty hot.
We can take advantage of all of this to cook food or lock in energy through solar panels. Our solar cookers for BFF are very simple – simply foil over the inside of a pizza box. The aluminum foil’s molecules create a very smooth shape that will reflect light. We cook on a black platform that will absorb light, and use foil above and around the black to reflect more light towards the platform.
We’ll affix some thermometers to the solar cooker and some differently colored shirts, to show where the light and heat energy are accumulating, but what’s more clear than to actually cook something? S’mores will be roasting in our solar cookers, and if we get a bright enough day, we should get some gooey, golden brown caramelized treats.
Everything’s better in threes, so we round the whole Stroller Hikes booth experience off with a craft: UV-sensitive bracelets. The Nobel Prize in Chemistry in 2008 was awarded for understanding and subsequently engineering fluorescent pigments. Since then, much of the world has paid more attention to these and other colors. Out of that interest, we now have inexpensive, widely available paints that are particularly sensitive to different forms of energy. The paint absorbs energy, which causes its molecules to change in shape, so new light energy makes it appear as a different color. Remove the energy source, and the molecules change back, and the new color is gone. Very cool! This is how glow-in-the-dark paint generally works. UV-Sensitive Beads absorb UV light, which warms up their pigments, causing the pigments to change shape. The new shape causes light that hits them to bend and break into new colors not seen before UV. At our booth, kids will make bracelets that can indicate if there is UV light in a room, under a tree, or in a sunny field. Cool!
So where do plants come in? Plants, like pretty much everything, don’t want to be eaten, so some produce stinky chemicals. Chemicals stink because they are volatile, or air-borne. The plant may make the chemical as a solid or liquid, then relies on heat to help the chemical hit the air. So… a plant with a dark enough pigment to absorb (rather than reflect) light, will get warmer in the sun, and the stink will take flight… to hit the “noses” of would-be-herbivores and repel them. Other plants use odors to attract, so may rely on pigments to indirectly attract pollinators with smell and directly attract them with color.
We hope you can join us for BFF this coming weekend, but if not, all of these crafts are quite inexpensive and easy to do at home. You’ve likely got foil and a box, some black and white, and some string for beads at home, and local craft stores like Joann Fabrics carry UV-sensitive beads.
-Debbie (Founder and President, Stroller Hikes), Holly (3), Max (7), and Andrew