Monthly Archives: July 2015

DIY Watermelon Explosion

Here’s a fun summer experiment that ends with watermelon EVERYWHERE! Be sure to wear proper eye protection…delicious debris will fly in all directions. You’ll need one watermelon, a LOT of rubber bands, and an outdoor area that can get very, very messy. Cover your explosion zone with a large tarp for easier clean-up!

Step 1: Place a rubber band around the middle of the melon.


Step 2: Repeat step 1 until…


Check out the huge ball of rubber bands flying off to the right! It’s easier to see in slow motion:

Step 3: Snack. (At least with what is left!)

It can take a few hundred rubber bands to create enough of a squeeze to shatter the watermelon rind (the size of that rubber band ball should give you an idea of the volume involved), but the results are worth it! We had a great time with this one and hope you will too.

#WhySpaceMatters: NASA’s Anniversary

If you’d like to know what’s out there in the universe, it’s an awfully exciting century to be alive! From Vostok to Hubble to New Horizons, ambitious feats of engineering are bringing our corner of the cosmos into fuller detail and color all the time. At AstroCamp, we’re all about harnessing the wonder of space exploration as fuel for passion and inquiry. We hope that some of the students who peer through our telescopes into the deep, dark beyond will keep looking and pushing the boundaries of human knowledge as part of the next generation of scientists.


Campers at AstroCamp are #whyspacematters!

Space matters because it stimulates curiosity, drives innovation, and lends context to our existence on Earth. It matters because it changes our perspective on everything. In honor of NASA’s anniversary, here are a few mind-bending ideas that show #whyspacematters to us.


Campers get a closer look at the conjunction of Jupiter and Venus. Credit: Andy Balendy

Look up at the night sky. You are experiencing a tiny gravitational pull from every star and planet you see, and hundreds of billions that you don’t see. Even weirder, your body is pulling back on each one! If you replaced the sun with a black hole of the same mass, Earth’s orbit wouldn’t change, but 8.3 minutes later we’d get very, very cold. That’s the amount of time it would take for the sun’s last light to reach Earth.

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Two black holes (shown in purple) in spiral galaxy Caldwell 5. Credit: NASA/JPL-Caltech/DSS

When you look out into space, you’re also looking back in time. The average distance to a star you can see with the naked eye is in the ballpark of 100 light-years. This means the image your eyes receive is about 100 years old. The closest star to earth is 4.22 light-years away. If it mysteriously disappeared right this second, we’d have no idea until 2019! The Milky Way and its nearest neighbor, the Andromeda Galaxy, are on course to collide in roughly 4 billion years, as our sun nears the end of its life. Galaxies are mostly empty space, so the odds of things actually smashing into each other are remote, but any life forms present at that time will witness a complete transformation of the night sky.

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New Horizons LORRI image of Pluto, 7/14/2015. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Over 70 years ago, within the memory of many people alive today, no spacecraft had ever left our home planet. As of this writing, 533 people have orbited Earth. 12 have walked on the moon. A telescope the size of a school bus floats in space, probing the history of the universe. Robots study nearby worlds on our behalf. Voyager 1, which has been sailing towards the distant stars since 1977, is now three times as far from the sun as Pluto, over 12 billion miles away from Earth… and counting!

Happy Anniversary NASA! Here’s to the bright future of exploring the great unknown.

Eureka! Buoyancy And More

Have you ever felt pressure on your body– especially in your ears– as you swim deep underwater? The deeper you go, the more pressure you feel. This is the core of a principle called buoyancy. Buoyancy explains why, in a liquid, what goes down just might come up!


Let’s think about how water affects this metal sphere. Pressure increases with depth, so the water at the bottom of the sphere pushes it up more than the water at the top pushes it down. The same goes for you – when you float vertically in the water, the pressure is always greatest at your feet. This unbalanced force, called buoyancy, is illustrated here:


Photo courtesy of

Buoyancy doesn’t care how heavy things are, just how much space they take up in the water. The buoyant force lifting an object up is always the same as the weight of the liquid that would normally occupy that space. If you push a beach ball underwater, the buoyant force pushes back with the weight of the water that the beach ball has shoved out of the way. Push a yoga ball under, and you’ll feel a push back equal to– you guessed it– the weight of a yoga ball full of water!

So, why do some things float and others sink? We can think of the answer as a battle between the forces of buoyancy and gravity. A rock is heavier than the amount of water it pushes out of the way. Gravity pulls down more than buoyancy pushes up, so the rock sinks to the bottom. A beach ball, on the other hand, is much lighter than a beach-ball-sized blob of water, so in this case buoyancy beats gravity. It floats! In general, if an object is less dense than water, it floats. If it’s more dense, it sinks.


In our Coke can experiment, we see that regular Coke is denser than diet. The sugar in the red can drags it to the bottom of the tank.

Buoyancy works in other substances, too. A helium balloon floats in air for the same reason a beach ball floats in the pool. Water stays in the pool because it’s more dense than air– if it wasn’t, it would float to the ceiling!

Explore Hydrogen: WARNING DANGER!

Hydrogen: it’s the most common element in our universe, the main ingredient in stellar fusion, and the lightest element of them all. We love to play with hydrogen in the classroom because it’s highly combustible, which means it’s great for explosions! In this experiment — which is not one we recommend for home DIY — we’ll fill soap bubbles with hydrogen and light them on fire.


Warning: Don’t try this at home!

Hydrogen and oxygen react to form water molecules. So, how do they create such violent explosions? The water molecules have less potential energy than the sum of their hydrogen & oxygen parts, and that extra energy has to go somewhere. It’s released as light and heat! This kind of reaction is called exothermic.


Warning: Don’t try this at home!

In this experiment we trap hydrogen inside of soap bubbles until we’re ready to trigger an explosion. Any container will do the trick, though, as long as it doesn’t block the activation energy. A balloon full of hydrogen creates a bigger fireball than the bubbles you see here. A single spark transforms a blimp filled with hydrogen into a massive firestorm– exactly what happened in the Hindenburg tragedy of 1937. Once the explosion is set in motion, it continues until all available fuel is consumed, for better or for worse.


Photo credit: NBC News

Instant Snow for Summer Fun!

With things heating up this summer, we wanted to just play in the snow! The stuff you just saw is called sodium polyacrylate. It is also known as waterlock, which shouldn’t be surprising considering what you just witnessed! Its ability to absorb an incredible amount of water makes it useful for certain purposes–like diapers and thickening agents–but it can also make for a super fun science project!.


We used about 30 grams of sodium polyacrylate, and poured about 1000 grams of water into it! Since all of the water was absorbed, the 30 grams of sodium polyacrylate became about 34 times heavier! The average adult in the US is about 180 lbs. For them, this would be the equivalent of going swimming and coming out at over 3 tons, which is about the size of a small adult Orca!


Even  after absorbing all of that, the snowy substance felt damp, but still could have absorbed more! Sodium polyacrylate has been called a super absorber for the fact that it has been known to absorb up to 300 times its own mass!

An interesting chemistry note: adding salt to the water and snow mix changes the properties of sodium polyacrylate immensely. Check it out below as the salk breaks down the mixture, resulting in truly wintery pile of wet, sloppy slush.

snow to slop

Enjoy your summer while you can!

Balloon Stabbing Science

How does this balloon stay intact? It’s got everything to do with our angle of attack.

Latex, the stretchy material most balloons are made of, is a polymer. Polymers are made of macromolecules, or long chains of repeated small parts. When a balloon inflates, the long molecule chains in its surface stretch out & make room for the air collecting inside.


The balloon isn’t stretched equally in all directions, though. It experiences less tension in two places: the knot at the bottom, and the point directly opposite the knot. You can usually see this point as a dark spot on the top of the balloon. These areas of least stress are ideal targets if we want to stretch the latex out even more…by stabbing it with a skewer, for instance!


Once the surface has been punctured, the polymer stretches tight around the skewer, keeping the air trapped inside the balloon. We coated our skewer with dish soap to make it more slippery and to help seal the gap between skewer and latex.

It’s important to be gentle during the stabbing process– stretching the polymer too much will cause those long molecule chains to tear, popping the balloon! It also helps to twist the skewer slowly as you break each surface (remember to aim for the dark spot at the top of the balloon on your second puncture). A careful touch, a little patience, and, you, too, can have a balloon kebab!



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