Eclipse experiments: temperature, light, crescents and sounds, without looking at the Sun

To do science with the eclipse you don’t need to look at the Sun for a single second: it’s enough to measure what happens around you. There are four experiments anyone can do: the temperature in the shade, the light, the crescents cast by a tree or a colander, and the sounds of animals. They work inside and outside the path: Málaga will have totality, and in Madrid the Sun will be up to 86.1% covered. Last summer there were also citizen-science projects with sound recorders, photometers and weather balloons; for 2027 we haven’t yet found any that has been announced.

The log sheet

Always note things down at fixed intervals, and start before first contact and carry on until after the last, so you have something to compare with. The Málaga sheet gives the percentage of the Sun’s disc covered according to the eclipseando engine, in Spanish time (CEST, UTC+2); you fill in the other columns:

In Málaga, totality lasts 1 min 49 s according to the IGN (Spain’s National Geographic Institute), around the maximum at 10:49. In Madrid the eclipse runs from 09:46 to 12:02, and the maximum, at 10:51, stays at 86.1%. The times for your own municipality are on when is it? and on its page, like the ones for Málaga or Madrid.

Temperature

What has been measured at other eclipses, and why the one on 2 August, in mid-morning, is a different matter, is in how much does the temperature drop during an eclipse, along with where to put the thermometer and how long to keep taking readings. Use the same thermometer in the same spot all morning, without moving it. If you’d like your data to be useful to others, NASA’s GLOBE Observer app lets you log air temperature and clouds during any eclipse.

Light

You can measure light with your phone if it has a light sensor. Phyphox, an app from RWTH Aachen University, reads the phone’s sensors (the light sensor is on its list, although not all phones have the same ones) and exports the data so you can make the graph afterwards. Leave the phone still, screen up and always in the same place, preferably in the shade rather than the sun so it doesn’t heat up. You don’t have to look at the Sun at all. At the end, compare your curve with the Sun-covered column on the sheet.

Crescents

During the partial phase, the gaps between a tree’s leaves and the holes in a kitchen colander project the bitten Sun onto the ground: dozens of crescents at once. How to do it, with the pinhole box and other viewers, is in the homemade viewer (in Spanish). The experiment is to photograph the same patch of ground, or the same card, every ten minutes and from the same spot. At the end you have the whole sequence, and you can compare how thin each crescent is with the percentage on the sheet. You look at the projection, never through the hole towards the Sun.

Sounds and animals

What animals do and what to watch for, we cover in the eclipse and animals (in Spanish). To turn it into an experiment, record the ambient sound with your phone kept still from a while before totality (or before the maximum, if you’re outside the path) until a while after, and note the time, the place and what you see. Also record at the same time the day before and the day after, so you have something to compare with: that’s what the Ecoeclipse project did with its recorders. And in the path, just before and after totality, look at the ground in case shadow bands appear.

Last summer’s citizen science

According to elDiario.es, a Spanish online newspaper, before last summer’s eclipse there were several projects in Spain open to volunteers:

• Ecoeclipse, coordinated by Airam Rodríguez and Irene Mendoza: more than 300 automatic recorders to log birds and bats over five days, the 48 hours before, the day of the eclipse and the 48 hours after.
• FreeDSM, by Eduard Masana of the Institut de Ciències del Cosmos (UB-IEEC) at the University of Barcelona: a low-cost photometer that the participants assembled themselves to measure the brightness of the sky, with humidity and temperature sensors. They went from about 20 volunteers to almost 100.
• Misión Globo Sonda Eclipses, by the Agrupación Astronómica de Madrid, an amateur astronomy association: 16 balloons, 13 teams and almost 100 people aged 9 to 85.
• Proyecto MEE, by the Agrupación Astronómica de Barcelona: photographing the stars near the Sun during totality with amateur equipment, to repeat Eddington’s 1919 experiment.

NASA has its own tool, GLOBE Eclipse, within the GLOBE Observer app. It was opened for the eclipses of 2017, 2019, 2020 and 2024 to collect observations of clouds and temperature, but not for last summer’s; its page notes that with the same app you can log clouds and air temperature during any eclipse. For 2027 we haven’t found any published call, from these projects or any others.

To look at the Sun: glasses with the EN ISO 12312-2 filter in all the partial phases, and no filter only during totality itself; how to check them, in our glasses guide. And if you’re doing these with children, the explanation to give them first is in explaining the eclipse to children.

Sources: Los experimentos científicos del eclipse en los que se podía participar — elDiario.es, Antonio Martínez Ron (in Spanish: Ecoeclipse, FreeDSM, the weather balloons and the MEE project, with their figures); Eclipse Overview — GLOBE Observer, NASA (which eclipses GLOBE Eclipse was opened for, that it was not opened for last summer’s and what can be logged during any eclipse); phyphox — RWTH Aachen University and its sensors (the app, the light sensor and the data export); eclipseando data (percentage of the Sun covered every ten minutes, times and maximums, skyfield + DE440s engine; length of totality in Málaga, IGN).