#Parallax angle how to#

If not, we provide instructions here on how to make a similar angle-measuring device from easily available materials.įigure 3: Setup for the angle-measuring activity. Activity: the geometry of parallaxįor this activity, you will need an instrument for measuring the angles between sight lines – a theodolite (see figure 1), if there is one in your school’s mathematics, physics or geography equipment. In the next issue of Science in School, we will describe a photographic method of using parallax measurements that is even more accurate and astronomically authentic. We have successfully used this activity, which takes between 30 and 45 minutes including setting up, with students aged between 13 and 17. The activity we describe here reproduces the basic geometry of parallax measurements, using simple devices to measure angles.

#Parallax angle download#

There is also a short web article about the history of parallax measurements, which you can download from additional material section w1. In this article, we describe an activity that explores the way astronomers use parallax to measure interstellar distances by working out the distance of a ‘star’ set up in a classroom. Currently, the ESA satellite Gaia, which was launched in December 2013, is measuring extremely accurate parallaxes for more than a billion stars in our galaxy, the Milky Way, increasing accuracy by a factor of about 200. Surveyors also use this kind of measurement to draw accurate maps of the surface of Earth. In the mid-19th century, astronomers used parallax to work out the first stellar distances. This effect has been used for centuries to determine distances in space w1. Now stretch your arm as far as it will go and, moving your thumb closer to your face, repeat the experiment of looking with each eye separately at different distances: you will notice that the shift in apparent position increases as the distance between your thumb and your eyes decreases. As you change eyes, your thumb appears to jump sideways in relation to the more distant background imagery – because your two eyes are in slightly different positions.

You can reproduce the effect by making the thumbs-up sign in front of your face and watching your thumb first with only your left eye, then only your right eye. This apparent change in position depending on distance is called parallax. Look out of a side window of a moving car or train, and you will notice that your view of objects changes with their distance: nearby bushes or trees seem to be rushing by, while a distant tree or building appears to move far more slowly. How far away are the stars? Explore in your classroom how astronomers measure distances in space.