Monthly Archives: August 2016

Three Things You Should Know About Telescopes

1) They Come in Three Flavors


Image credit: Dale Mahalko.

All telescopes fall into one of three categories: refracting, reflecting, or combination. Most modern telescopes favor the reflector method for practical reasons. It’s easier to create and transport a large, precise parabolic mirror than a lens of equal usefulness. Mirrors also eliminate the problem of chromatic aberration (shown above; notice the discolored edges on the small boxes and the arm of the glasses). Chromatic aberration is an optical distortion resulting from light of different wavelengths emerging from a glass lens at varying angles.

2) Magnification Isn’t the Point


Image credit: NASA/JPL.

At least, it’s not the only one. If a telescope zoomed in on the image your eye records of, say, Jupiter, you’d see a large, fuzzy blob. Light collection in the human eye is limited by aperture size and perceptual frame rate. Poor light-capturing ability translates to blurry views of distant, seemingly tiny objects. Magnification is nice, so the small eyepiece lens on a telescope does enlarge the final image, but the scope’s large primary lens or mirror serves a different purpose: gathering lots and lots of photons. The image above shows Neptune as observed by the Hubble Space Telescope, whose primary mirror measures eight feet in diameter!

3) You Can Build A Simple Model Out of Stuff You (Probably) Already Have

The quality will be far from professional, but this DIY project is a fun, easy way to explore the concepts at work in a reflecting telescope. Set up a curved shaving/cosmetic mirror opposite the light source you want to observe (try a flashlight, or the moon if you’re feeling crafty…NEVER THE SUN). This is your primary mirror. Place a flat mirror in between the primary mirror and light source, facing the primary mirror– that’s your secondary mirror. Position yourself behind the primary mirror so you can see its reflection in the secondary. Play with each mirror’s angle and distance to resolve your target image. How does it turn out? What are the limitations of the system?

Take this project further by experimenting with mirror & lens combinations (try a magnifying glass lens), measuring mirror and lens focal lengths, and/or mounting your optical components along a cardboard tube or other support structure. Again, do not use these methods to image the sun. Irreversible injury and/or fire may result.

For a higher-quality alternative, try the Galileoscope, a user-friendly refracting telescope designed for educators and curious people. It’s easy to assemble without tools or glue. Watch below as our Galileoscope goes from a pile of parts to a working instrument (also not safe for sun-gazing).


Written By: Caela Barry

Curveball Science

The Magnus effect allows pitchers to throw curveballs, soccer players to bend kicks around defenders, and golfers to launch drives along near-triangular flight paths. This fun physics phenomenon relies on the difference in relative airspeed at various points on the surface of a round object.


Viral video captures the Magnus effect in action, 2015. Credit: YouTube channel How Ridiculous. Full footage:

Picture a ball moving through the air while spinning. For the ball to experience a net force, its axis of rotation must be oriented so that some points on the ball’s surface move in the same direction as its trajectory (let’s name one of these points A) while some move the other way (we’ll call an example of this type B).


At point A, the air dragged along by the ball’s surface and the air farther away rush past each other in opposite directions; at point B, they move in the same direction, although one still moves relative to the other (unless rotational speed and flying speed are perfectly matched). This is a bit like the difference between two cars going in opposite directions on the highway and a car in the fast lane passing one in the slow lane.

Like a boat traveling through water, the ball leaves a wake behind as it cuts through the air. The differences between relative airspeeds around a rotating ball cause its wake to pull to one side, resulting in an asymmetrical imbalance of air pressure. This lopsided push bends the ball’s path as it travels.


A DIY-friendly demonstration of the Magnus effect. Unlike the basketball, which had a backspin as it fell down the dam, the paper roll’s front edge is spinning along with its trajectory. This results in a backwards arc.

The Magnus force affects cylindrical objects in a similar way. Try this at home with a sheet of paper, rolled up and taped into a cylinder. Allow the paper tube to roll off the edge of an angled surface to give it a uniform spin, and watch its path curve!

Written By: Caela Barry

Fire Tornado!

Tornadoes are born when extreme weather circumstances come together. Their short, destructive lives are still not fully understood, but one leading theory goes like this: sometimes, winds at different altitudes blow at different speeds, rolling the air between them into a horizontal, rotating cylinder. If a supercell thunderstorm is nearby, the spinning column can be pulled into the maelstrom. Once the tornado is vertical, its lower end has the potential to touch down and wreak havoc on Earth’s surface.

West Texas wildfire

West Texas wildfire. Image credit: Texas Forest Service.

In a real supercell, swirling updrafts are created by variations in temperature, pressure, and wind speed in the storm area. In this experiment, we simulate updraft conditions by physically pushing the air into a rotating column formation using a window screen rolled into an open-ended cylinder. Without the screen (and the wind it generates), the spinning fire doesn’t do anything especially interesting. That’s because of Bernoulli’s principle: the faster a volume of fluid moves, the more neighboring molecules are sucked into the breeze. By giving the air a push, we draw extra oxygen in towards the flame.


Fire tornadoes are spectacular in the lab, but you don’t want to see one in nature. These twisting ropes of flame have played a tragic role in several of the greatest conflagrations in human history. From Chicago to Peshtigo to Tokyo and beyond, they’ve spread blazes with devastating speed and blocked victims from reaching safety in nearby bodies of water.

At least one team of researchers is working towards harnessing the power of the fire whirl for practical purposes. Hot, clean-burning blue fire tornadoes show potential as a tool for improved oil spill cleanup.

As with any experiment involving combustion, check in with an adult, keep a fire extinguisher on hand, and exercise caution if you decide to make a flaming tornado at home. We used a turntable with a heat-safe covering, a non-flammable window screen stapled into a cylinder, duct tape, a glass flask, and a few ounces of 99% isopropyl alcohol to create our fire whirl.

Written By: Caela Barry

How To Trap a Laser

Ever notice how, when you look into rippling water, you see slices of what’s below the surface mixed with broken reflections of the world above? When light hits a boundary between two different tirUFLmedia, it can either travel ahead into the second medium (refraction), bounce back into the first (reflection), or do a little of both. What actually happens depends on what it’s traveling through and into and the incident angle of the light rays. (Diagram at left courtesy of the University of Florida.)

Light travels fastest in a vacuum. It propagates more slowly (although still incredibly fast) in substances like air and water. The more optically dense a medium is, the slower light travels through it.

Picture a beam of light hitting a boundary from the slower or more optically dense side, e.g. traveling through water towards air. Sometimes, depending on the angle of incidence, the light bounces back completely instead of transitioning into the faster medium. In this situation, the image from underwater never reaches the eyes of an observer above the surface. The information is completely trapped within the slower medium. This is called total internal reflection, and it’s everywhere.


A mirage is an example of total internal reflection in nature. Photo by Brocken Inaglory.

If you’ve ever seen the illusion of a puddle of water on the road on a hot day, you’ve experienced total internal reflection in nature. Hot air near the ground is less optically dense than the cooler air above, so light travels faster through it. Rays of sunlight that approach the ground from a certain range of angles bend up and away as they near the surface of the road, carrying the image of the sky– which looks like water– to your eyes!

Humans take advantage of total internal reflection, too. Fiber optic cables shuttle electromagnetic information all over the world. Endoscopes use fiber optic technology to provide a non-surgical window into the human body.


The stream of water in this experiment partially traps a laser, making it a not-so-great fiber optic cable. The laser signal isn’t completely transmitted from end to end; some light is lost through the sides as the stream becomes turbulent. Escaping light gives the stream a bright green glow.

Try this at home by drilling a hole near the bottom of a clear container, filling it with water, and shining a small laser straight through the container and into the exiting stream!

Written By: Caela Barry

Levitate a Soda Can

Did you know that Bernoulli’s principle is a statement of conservation of energy? The sum of kinetic and potential energy is constant in every closed system. In fluid dynamics, potential energy is an expression of the pressure within a volume of liquid or gas. When a fluid moves faster (its kinetic energy increases), pressure (potential energy) must decrease to compensate.


Image credit: University of Oregon

This coupling of behaviors creates fun scientific results! We’ve explained before how to levitate a beach ball with a leaf blower. Today, we’re scaling Bernoulli’s principle down to tabletop size for a super-doable DIY experiment. All you need is an empty soda can and a mug big enough to contain it.


Place the can inside the mug and blow air into the gap between the two containers. Your breath moves faster than the surrounding air, so it creates an area of low pressure around the sides of the can. Stagnant air trapped underneath the can expands to fill the partial vacuum, pushing the can upwards. With a little practice, you’ll be able to jump the can from one mug to another!

Written By: Caela Barry  

DIY Fireproof Cash

smallmoneyburnWe soaked this $5 bill in flammable rubbing alcohol and then lit it on fire. So how did it survive? Does it have something to do with the bill itself?

This demonstration is impressive with money, but we haven’t been able to find an example of it using other materials. Many people have asked us what would happen to regular paper in the same situation. This opened up the chance for us to do some real science! We repeated our experiment, replacing the dollar bill with standard white paper and a brown paper napkin. Neither of these caught fire either.

The key to this trick is the part that stayed the same in all three experiments: a solution of rubbing alcohol and water. Water has a high specific heat, so changing its temperature takes a lot of energy, as we’ve seen before. Unlike water, rubbing alcohol is very flammable. It easily burns away until most if it is gone, leaving behind a mixture consisting primarily of water.  

By lighting pools of alcohol on our fireproof table tops, we measured the temperature of the water left behind after burning off as much of the alcohol as we could. Here are the results:


smallpaperDespite being literally covered in fire for thirty seconds, the water temperature only climbed by 11.8 degrees Fahrenheit! The water in the rubbing alcohol mixture is protecting the money with its high specific heat, preventing the paper in all of the above examples from getting hot enough to burn. As such, when performing this experiment, it’s very important that we completely soak the money (or other experiment subject). If any surface is exposed, it will catch on fire! After the flame has gone out, the paper doesn’t even feel warm to the touch.

Only try this at home with adult permission and a fire extinguisher!

Written by: Scott Alton


The (Almost) Invisible Fuse

When you light a candle, wax melts and travels up the wick via capillary action. As it gets close enough to the heat source, the wax vaporizes and ignites, providing more heat, which melts more wax, which is wicked up into the flame in turn. The cycle continues until fuel runs out, oxygen is depleted, or the heat source is removed (i.e. the candle is blown out).

In general, solid and liquid fuels burn when heat exposure causes them to release flammable vapors. Byproducts of gaseous combustion float away as smoke.


Extinguish a candle, and some wax vapor is left over in the smoke trail. In the moment before it dissipates, this column of flammable gas can act as a fuse and carry a flame back down to the candle wick.

This experiment depends on Earth’s gravity to work. Here on our home planet, the behavior of fire is predictably familiar. Warm air around the flame rises. Cool air rushes in to fill the void at its base, carrying a fresh supply of oxygen. The combustion reaction continues, heating more air and propagating the convection cycle.


Image credit: NASA/FLEX-2

Without Earth’s gravity to pull cool, dense air downward, hot air doesn’t float. For this reason, flames in space burn spherically, and a smoke trail would never rise from an extinguished fire!

Written By: Caela Barry


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