# Making Nitrogen Balloons Float

When you blow up a balloon with your breath, you’re filling it with a mixture of nitrogen, oxygen, and a little bit of carbon dioxide. And when you let go of it, it falls down to the floor. Why does it do this? And how could we prevent it from doing so?

Think of it like rocks in water. If you throw a stone into a river, it will sink to the bottom. This is because the rock is more dense than the water around it, due to its higher mass that’s concentrated in a smaller volume. The water tries to push back against the rock with a buoyant force, but the force of gravity is stronger, so the rock sinks. In our example, the balloon filled with nitrogen, oxygen, and carbon dioxide is the rock, and the atmosphere around us (made up of nitrogen and oxygen) is the water. Even though the gases inside and outside the balloon are approximately the same, the balloon material adds to the weight, causing it to sink down. If we wanted to get the balloon to float, we would have to either decrease its density or increase the density of the air around it. By putting a low-density gas like helium or hydrogen inside the balloon, we can make it light enough to float.

But the cooler thing to do is to change the density of the air around the balloon! We can do that here at AstroCamp by allowing dry ice to heat up and change into its gaseous form: carbon dioxide. The higher density of carbon dioxide makes it so that the buoyant force is way stronger on the balloon, which causes it to float!

Density experiments are really cool. You can actually learn a lot about them if you try it at home! Try mixing cooking oil and water with each other, then put object like rocks or pieces of wood inside! See what happens and let us know in the comments below!

Written By: Scott Yarbrough

# Lights and Lasers: How the Glow Wall Glows

One of the most popular classes at AstroCamp is Lights and Lasers, where students learn about the different energies and properties of light. The Lights and Lasers room is easily recognizable because of its Glow-in-the-Dark Walls. Once you turn the lights off, these awesome walls glow a vibrant green, slowly dimming until you shine light on them again.

These walls have a physical property known as phosphorescence. It is a type of photoluminescence: an emission of light occurring when an object absorbs and releases photons. Other common types include bioluminescence — a chemical reaction in living organisms that give off light — and electroluminescence — the process by which LEDs give off light.

Phosphorescence works by absorbing photons into the object’s electrons. This bumps those electrons into a higher energy level. But the electrons cannot then easily reemit the photons to return to their ground state: the electron becomes “trapped” and it requires a “forbidden transition” to return to its lower energy.

However, due to quantum mechanics, this forbidden transition can still happen, but it does so at a fairly slow rate. This allows the material to “store” the light and let it out slowly, sometimes taking hours to let out all of its light! This same material that we use for our glow wall is what is used for things like glow in the dark stickers! So even though they seem simple, next time you see them you’ll know that there’s a lot more going on than what first appears!

Written By: Scott Yarbrough

# Black Holes Explained (Sort of)

Black holes are a confusing topic in astronomy. You’ve heard about them starting from a young age, but whenever you ask someone for more information about them, there’s a whole lot of “I dunno”s. The truth is, black holes have been romanticized by science fiction, when in fact they are nothing more than an oddity of physics (albeit still pretty cool). Once you understand a few basic rules of physics, learning about black holes is easy.

Step 1: Gravity

The first step on the road to understanding black holes is understanding how gravity works. An object with mass will cause a bend in spacetime, affecting other objects around itself. This effect is what causes gravity. The more mass something has, the more gravity it produces. The force of gravity gets weaker the farther you get from the center of mass proportional to the inverse of its distance squared. Yeah, I know, that sounds confusing. Maybe it’s easier if you see the equation for calculating the force of gravity.

In this equation, M is the mass of the larger object, m is the mass of the smaller object, G is the universal gravitational constant, and r is the distance between the two objects. If you double the distance between two objects, then the force of gravity is ¼ what it was before. If you triple it, then the force of gravity is only ⅑ the original.

Step 2: Escape Velocity

In order to escape the gravitational field of a massive object, you need to attain a specific speed, called its escape velocity. It’s calculated using the force of gravity, taking into account the mass of the large object and how far away you are. Once something is going at minimum the escape velocity, then it is no longer captured by the massive object.

Step 3: Singularity (or, infinite density)

Density is an easy calculation, as seen below.

Where m is mass and V is volume. As mass increases or as volume decreases, density goes up. In a black hole, the volume is essentially 0, which causes the density to approach infinity. This creates what is called a singularity.

Putting it all Together

When the most massive stars in the universe go supernova, the force of the explosion causes the core of the star to get smaller and smaller, essentially packing it all into a volume of 0. This point of infinite density creates such a huge bend in spacetime that it creates a singularity. At a certain distance away from this singularity, the force of gravity the escape velocity reaches the speed of light.

As defined by the theory of relativity, nothing in the universe can go faster than the speed of light. So if the escape velocity of this object at a certain distance is higher than that, then not even light can escape the singularity. With no light escaping, the object and the space around it gives off no light.

This is the black hole.

There’s a lot more that goes into defining black holes, such as its mass, spin, etc., but that’s just icing on the cake. There you have it. There’s so much more to learn about black holes, but knowing even this much gives you the tools you need to understand them at a fundamental level.

Written By: Scott Yarbrough

# 3D Printing an Asteroid

NASA has always been about accomplishing crazy. In the 1960s, the idea of people walking around on the moon was ludicrous, but NASA got them there anyways. Now, NASA is performing another crazy feat: sending a probe to an asteroid, collecting rock samples, and returning that probe to Earth. Additionally, the probe has created a digital map of the asteroid which we can recreate, simply by using a 3D printer.

In September 2016, the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer space probe (OSIRIS-REx for short) was launched aboard an Atlas V rocket. It quickly made its way into space and began its journey towards the asteroid designated 101955 Bennu. This journey lasted over two years as the robe used low-power thrusters and gravity assists from Earth to reach its destination.

Side by Side – 3D Printing Asteroid

OSIRIS-REx reached Bennu in December of 2018, and as it approached, it used its long-range PolyCam sensors to map out the surface of the asteroid. After arriving, OSIRIS-REx used its short-range cameras to take even higher resolution images of Bennu’s surface. NASA scientists used that data to create 3D models and released them to the public!

Since we’re lucky enough to have a number of 3D printers here at camp, we decided to print our very own Bennu asteroid! You can see the results below, but if you want to have your own version of the asteroid, you can find the files at https://www.asteroidmission.org/updated-bennu-shape-model-3d-files/

Written By: Scott Yarbrough

### WELCOME TO OUR ASTROCAMP BLOG

We would like to thank you for visiting our blog. AstroCamp is a hands-on physical science program with an emphasis on astronomy and space exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and astronomical happenings. This blog has been created by our staff who have at least a Bachelors Degree in Physics or Astronomy, however it is not uncommon for them to have a Masters Degree or PhD. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science, space and astronomy information. Feel free to leave comments, questions, or share our blog with others. Please visit www.astrocampschool.org for additional information. Happy Reading!