Using Smartphone Camera Technology to Explore Stellar Parallax: Method, Results, and Reactions

Abstract

Abstract The use of a smartphone, with both still and video capabilities, to develop the concepts surrounding stellarparallax is described. The hands-on activities generate useful discussion amongst high school students. Reactionsof both students and teachers are presented. 1. INTRODUCTION Stellar parallax is a concept that is dealt with infrequently in the high school classroom other than by qualitativeconsideration of stereoscopic parallax and argument by analogy, such as that outlined in Zeilik (1998). The mostcommon approach involves students being asked to view their finger held at arm’s length and first viewing itfrom one eye and then the other. They “see” their finger’s apparent movement against the background of theroom. Following this qualitative approach, the unit of distance used in astronomy is introduced from adefinitional point of view: “The parsec is the distance of an object at which the angle subtended by a baselineequal to the distance between the Earth and the Sun is one second of arc.” This description is quite abstract,however, and it is unlikely that students will really get a conceptual feel for the idea of a parsec as a distancemeasure from an abstract mathematical statement. As the parsec is the fundamental unit of distance inastronomy, it is important that students have some strong insight to what this unit actually means (Marin 2010).We assessed a sample of diagrams available on the internet using a Google Image search. The first 50 diagramspresented from the search term “Stellar Parallax” were examined. Out of the 50 diagrams, 18 showed thealternative conception that all stars in the night sky “wobble” in a straight line, a further 20 showed the specialcase, where the star is on the ecliptic equator where they actually do wobble in a straight line, and a further 7 hadmajor faults. Only five out of the 50 diagrams accurately represented the relationship between the Earth–Sunorbit and the parallactic ellipse in the sky. That is to say, of this sample of 50 diagrams, only 10% could beconsidered to be scientifically accurate and a complete conceptual representation of stellar parallax.The experimental determination of stellar parallax is seldom dealt with in the science classroom because theparallactic angle is so small. Students have little, if any, idea of how astronomers collect their data because theydo not normally conduct the experiment first successfully executed by Bessel in 1838 in measuring the parallax