Sun trace


This experiment has been conducted on the 22nd December 2019 (winter solstice). Here we present the results. The original description can be found further down.

Without further ado, here is the result of the experiment:

Black points represent the location of a user who has submitted a measurement. Red crosses represent the calculated location of the sun (average over one hour in five minute intervals, see below) and the blue line a fit to the sun’s path. As the sun was traced during the winter solstice, this corresponds to the axial tilt of Earth. The fit yielded 23°.

The red crosses are obtained for a reference time at five minute intervals. For each reference, the data points of the past hour are used to calculate the position of the sun. Then from these positions, 50% outliers are removed by iteratively calculating the average location, removing the measurement that is farthest away and then repeating this over until 50% remain.

Here is an animation of the submitted data over time:

(Black lines are great circles from the users position to the individually calculated sun positions. Note that the representation glitches when crossing the edge of the map.)

If you want to play with the original data set as contributed by the users, you can download it here. This data set contains every submission by every user with all the original data with only minor changes to ensure the user’s anonymity:

  • The user ID has been replaced by a simple unique number.
  • Latitude and longitude have been rounded to two decimals to mask the location while retaining enough precision for calculations.

The columns are the timestamp of submission, a unique ID to match individual users, latitude, longitude, altitude, azimuth and magnetometer calibration. The magnetometer calibration is an estimate of the calibration quality by the phone’s operating system. Zero means that the magnetometer is not calibrated and three is the highest possible calibration quality.

Original instructions

[French] [German] [Portuguese] [Taiwan / Trad. Chinese]

Preview of the trace so far and the contributions from the past 15 minutes.

This is a collaborative experiment, which is planned for the 22nd December 2019 (winter solstice). We try to track the movement of the sun across the sky by users world-wide. And you can help us!

Simply open this experiment in phyphox, point your phone at the sun at different times across the day (22nd December 2019) and submit its position to us.

There is a simple way to ensure that your phone is aligned well. Just look at its shadow. If it is as small as possible, your phone is pointing directly at the sun.

After the event, the data will be usable by teachers in their courses and by students who want to analyze it. Of course, we will also make it available on this page.