A classroom analogy demonstration showing how astronomers, looking at stellar luminosity, look for traces of orbiting exoplanets.
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Theory
An exoplanet orbiting a distant star will block a small fraction of light from that star if its orbiting geometry leads it to transit between the star and an observer on earth. By measuring the total luminosity from the star during transit, astronomers can look for "dips" that can represent the existence of an exoplanet.
To show this in a classroom setting, we can create analogies of the three things needed for this kind of measurement: (1) the distant star, (2) the exoplanet, and (3) the observer measuring the luminosity change when (2) moves in front of (1).
For a star, we used an LED flashlight pressed into a styrofoam ball. It looks great on the video (if we say so ourselves) but any bright "circle" can be used. We recommend not using a direct source of light like a lamp or other light source shining directly into the observer. Since all we are looking to do is measure light blockage, you just need a bright background for the exoplanet to travel in front of. A good "star" can be a piece of dark construction paper with a large circle cut out to it and a piece of white paper glued behind.
For the telescope, we use a PocketLab Voyager, which has an on-board light sensor. You can try to use more available tools such as the PhyPhox app on a smart device but we warn against doing that without lots of testing. PhyPhox results vary wildly depending on the device being used.
For an exoplanet, you need a smoothly moving sphere, smaller than your choice of star. We used an elaborate sir track system, but you could easily accomplish something similar with a long arm pendulum, swinging in front of the "star". The important thing is to have the "exoplanet" moving smoothly and slowly between the star and telescope. The smoother and slower, the better the data will look.
Apparatus
- LED Flashlight
- Styrofoam Ball
- Air Track with cart and ball
- PocketLab Voyager (with device for data taking)
- Dark backdrop
Procedure
- Place LED flashlight into the back of a styrofoam ball. You will need to carve out a space in the ball to insert the flashlight. Once combined, mount the ball on a three-finger clamp and place a dark background around it.
- Mount the light sensor so as to directly face your star. If using the PockeltLab device, please note that it has a flashing LED on its face that really interferes with careful light measurements. It can't be blocked externally. I ended up opening it up and disabling (ie destroying) the onboard LED.
- Place the air track bound exoplanet in front of the sun. Adjust the angle of the track so that the cart moves slowly from release between the star and the detector.
- Record and plot the data. Experiment with larger and small "planets" as well as with transit speeds. If you use the PocketLab voyager, you can also experiment with data rates vs transit times.
