Null Results, Real Learning: Geomagnetic Response to an X1.8 Solar Flare with Research-Grade and Smartphone Magnetometers in a Citizen-Science Classroom Activity

TL;DR

This study evaluates smartphone magnetometers for geomagnetic monitoring during the 4 November 2025 X1.8 solar flare, using co-located measurements with a research-grade Geometrics G-857 proton magnetometer to establish a quantitative baseline. It demonstrates a substantial systematic offset of about $+626\,\mathrm{nT}$ between smartphone and G-857 readings and only weak, negative coherence in minute-scale variability ($r\approx-0.38$), indicating smartphones cannot reliably detect nanotesla-scale flare signatures at mid-latitudes. The work frames smartphones within an instrumentation ladder that connects research-grade observatories to citizen-science networks, highlighting strong educational value through explicit NOS reflection, data handling practice, and authentic inquiry, while also acknowledging the limits of low-cost sensors for precise space-weather measurements. The findings support deploying tiered magnetometer networks (from professional to community kits) to broaden participation and spatial coverage, with smartphones serving as engagement and context tools rather than primary quantitative sensors.

Abstract

Introductory college Earth and space science courses offer rich opportunities for citizen science projects. One especially compelling context is Earth's geomagnetic field: a self-excited dynamo in the liquid outer core generates a global field that couples Earth's interior to solar forcing, providing a natural laboratory for space weather education. We tested the viability of smartphone magnetometers for quantitative monitoring during the 4 November 2025 X1.8 solar flare, linking planetary magnetism, space weather, and authentic undergraduate research. Co-located observations were obtained with a Geometrics G-857 proton-precession magnetometer and tri-axial smartphone sensors logging via Physics Toolbox in a course-based undergraduate research experience (CURE) emphasizing the Nature of Science (NOS). Fourteen one-minute paired averages spanning 17:27-17:40 UT revealed a systematic smartphone bias of about 630 nT (95% confidence interval 550-710 nT) relative to the G-857 and a weak negative correlation (r ~ -0.4). Smartphone magnetometers thus lack the precision and calibration stability needed for nanotesla-scale flare signatures but remain valuable as pedagogical and engagement tools. We frame smartphones within a tiered instrumentation ladder linking research-grade observatories, intermediate-cost community magnetometers (for example, HamSCI Personal Space Weather Stations), and smartphones as high-engagement entry points to geomagnetic and space weather studies. This hierarchy aligns citizen science with open data protocols and NOS pedagogy, transforming low-cost sensing into epistemically grounded inquiry suitable for introductory college laboratories.

Figures (5)

• Figure 1: (a) Collaborative observations of multi-parameter data collection of the atmosphere, geomagnetic field, and the Sun. Observations completed, while not a part of this study, included meteorological conditions (wind speed, humidity, temperature, barometric pressure), generalized ionizing radiation using a Geiger counter, and sunspot measurements using multiple telescopes, chiefly two Seestar S50 all-in-one smart telescopes and a Celestron SkyProdigy 6 computerized telescope, all with solar filters. (b) Example astrophotograph of the Sun using default Seestar S50 specifications around the time of the 4 November 2025 X1.8 solar flare.
• Figure 2: Multispectral images of the Sun taken by the Solar Dynamics Observatory (SDO) using the Atmospheric Imaging Assembly (AIA) instrument, accessed through the Helioviewer Project. Panels (a) and (b) show a zoomed view of the flaring active region in a hot 94 Å band, emphasizing the compact flare core and overlying coronal loops; panel (c) shows the same region in a 1700 Å band that highlights the underlying sunspots and chromospheric structure; and panel (d) reveals extended flare structures and surrounding arcade in 175 Å. The bright arch-like features visible in panel (d) are coronal loops---distinct, arch-shaped structures of relatively dense plasma confined within magnetic flux tubes, anchored at two footpoints in the photosphere and extending upward through the transition region into the lower corona. In each panel, overlays and markers indicate the region of interest and sampling locations used in our analysis of the 4 November 2025 X1.8 flare.
• Figure 3: Unprocessed total magnetic-field observations with a smartphone magnetometer over UT 04:17:33 to 04:17:40.
• Figure 4: Processed total magnetic-field observations with a smartphone magnetometer, showing 10-second sample averages that substantially reduce the number of data points relative to the raw high-cadence data. These observations are over UT 04:17:33 to 04:17:40.
• Figure 5: Processed total magnetic-field observations with a smartphone magnetometer and the G-857 magnetometer, showing one-minute averages over the broader flare-centered window.