Science on This Day: December 18 | The Talking Satellite, the Electron and a Changing View of Earth
December 18 brings together three stories that show how scientists use technology to understand and connect our world. In 1958, Project SCORE demonstrated that a satellite could relay communications from space. In 1856, physicist J. J. Thomson was born; his later experiments helped reveal that atoms contain smaller, negatively charged particles called electrons. And in 1999, NASA launched the Terra satellite, beginning a major programme of observing Earth's land, oceans and atmosphere from orbit.
These events connect physics, astronomy, chemistry, environmental science and engineering. They also offer an opportunity to discuss how scientific instruments extend our abilities: satellites allow information to travel around the planet, experiments reveal particles too small to see directly, and Earth-observing spacecraft help scientists investigate environmental changes across vast regions.
December 18, 1958: Project SCORE launches the first communications satellite
Today, satellite communication is part of everyday life. Satellites help deliver television broadcasts, connect remote communities, support communications at sea and provide links for emergency services. But the technology had to begin somewhere, and one important milestone occurred on December 18, 1958, when the United States launched Project SCORE, widely recognised as the world's first dedicated communications satellite.
SCORE stood for Signal Communications by Orbiting Relay Equipment. The project was an experiment designed to test whether a satellite could receive, store and retransmit messages between Earth and space. It was launched aboard an Atlas rocket, and the satellite's equipment included radio receivers, transmitters and a tape recorder.
The satellite demonstrated two important approaches to communication. It could receive a signal and retransmit it to another location, and it could store a recorded message before broadcasting it later. This second capability made Project SCORE particularly memorable. The satellite carried a recorded Christmas message from US President Dwight D. Eisenhower, which was transmitted back to Earth on December 19, the day after launch.
The message was a demonstration of what the technology might make possible. For the first time, a human voice was broadcast from an artificial satellite in orbit. SCORE operated for a relatively short time, about 35 days, but it showed that satellites could play a practical role in communication systems.
It is important not to confuse this early experiment with the communications satellites used today. SCORE operated in a low Earth orbit and demonstrated basic store-and-forward and relay functions. Later satellites developed more sophisticated systems, including satellites in geostationary orbit that appear to remain above roughly the same point on Earth. Modern communication networks also rely on ground stations, antennas, signal processing and interconnected networks.
Nevertheless, SCORE helped demonstrate that space could be used as part of the world's communications infrastructure. The idea of using an orbiting object to carry messages had moved from possibility to practical demonstration.
Classroom connection: How do satellites send information?
This event is a useful introduction to electromagnetic waves and communication technology. Students can investigate how radio waves carry information and how a receiver converts a signal into something useful. They could compare a direct communication link between two distant locations with one that uses a satellite as a relay.
A discussion question might be: Why might a satellite be useful for communicating with a remote island, a ship in the ocean or a research station far from a major city? Students can consider distance, line of sight, terrain and the availability of ground-based infrastructure.
For older students, compare SCORE's store-and-forward system with modern satellite communication. What are the advantages of sending a message immediately, and when might storing information until a suitable transmission opportunity be useful? This could lead to discussions of communication delays, data storage and the engineering challenges of operating equipment in space.
My free Jupiter's Moons infographic, slides, podcast and quiz set offers another way to bring space science into lessons. Although Jupiter's moons are not communications satellites, the resource can help students explore how observations and spacecraft technology extend our understanding beyond Earth.
December 18, 1856: J. J. Thomson is born
Joseph John Thomson, usually known as J. J. Thomson, was born on December 18, 1856, in Cheetham Hill, near Manchester, England. His research would help transform the scientific understanding of atoms.
By the late nineteenth century, scientists had evidence that matter was made of atoms, but the internal structure of those atoms was still uncertain. The atom was often treated as the smallest unit of a chemical element. Thomson investigated cathode rays, which are produced when an electric voltage is applied across electrodes inside a tube containing gas at low pressure.
Cathode rays behaved in ways that suggested they were made of charged particles. Thomson investigated how the rays responded to electric and magnetic fields. By studying their deflection, he could estimate the relationship between the particles' electric charge and mass. His results, published in 1897, supported the conclusion that cathode rays consisted of tiny negatively charged particles present in atoms.
These particles became known as electrons. Their discovery was significant because it showed that atoms were not indivisible: they contained smaller components. Thomson's work changed the direction of atomic physics and helped establish the electron as a fundamental part of matter.
Thomson later proposed an early model of atomic structure in which negatively charged electrons were embedded in a region of positive charge. This model is often called the "plum pudding" model. It was eventually replaced after later experiments, particularly Ernest Rutherford's investigations of alpha-particle scattering, showed that atoms have a small, dense nucleus.
This progression is an excellent example of how scientific models change. Thomson's model was not the final answer, but it reflected the evidence available at the time. As new experiments revealed more about atoms, scientists developed better explanations.
Thomson received the 1906 Nobel Prize in Physics for his theoretical and experimental investigations into the conduction of electricity by gases. His work also influenced future generations of physicists, including his son George Paget Thomson, who shared the 1937 Nobel Prize in Physics for demonstrating the diffraction of electrons by crystals.
Classroom connection: How do we know atoms contain smaller particles?
Thomson's work is a useful way to introduce the relationship between evidence and scientific models. Students cannot directly observe individual electrons with their eyes, but scientists can investigate their properties by observing how they behave in electric and magnetic fields.
Ask students to explain why the deflection of cathode rays was evidence that they carried electric charge. What would scientists expect to observe if the rays were neutral? How might changing the strength or direction of a field affect the path of a charged particle?
For middle school students, this can be simplified into a discussion of how models help us explain things that cannot be seen directly. For older students, Thomson's experiments can lead into charge-to-mass ratio, electric fields and the development of atomic theory.
The story also illustrates why a scientific model should not be treated as an unchangeable fact. Thomson's model helped explain some observations, but further evidence led to its replacement. Students can compare early and modern models of the atom and identify the evidence that led scientists to revise their explanations.
December 18, 1999: NASA launches the Terra Earth-observation satellite
The first two events focus on communication and the structure of matter. The third turns our attention towards the planet we live on.
On December 18, 1999, NASA launched Terra from Vandenberg Air Force Base in California. Terra became a major part of NASA's Earth Observing System, a programme designed to investigate how Earth's land, oceans and atmosphere interact. Rather than studying just one place or one type of environmental process, Terra carries several instruments that collect different kinds of observations.
These instruments measure different properties of the Earth system. The Moderate Resolution Imaging Spectroradiometer, known as MODIS, collects observations that help scientists investigate vegetation, clouds, aerosols, fires and changes in land and ocean conditions. Other instruments measure thermal emissions, the movement of atmospheric pollutants and the way sunlight is reflected and scattered.
Terra travels in a near-polar, sun-synchronous orbit at an altitude of about 705 kilometres. Its orbit allows it to observe different parts of Earth as the planet rotates beneath it. This is particularly useful for environmental monitoring because researchers can collect observations over large areas and compare them across seasons and years.
Satellite observations help scientists investigate questions that would be difficult to answer using measurements from the ground alone. For example, researchers can monitor changes in vegetation over large regions, study the distribution of atmospheric aerosols and examine patterns in Earth's energy balance. When observations are collected consistently over long periods, they can help scientists distinguish short-term changes from longer-term trends.
Terra's measurements do not automatically provide a complete explanation of every environmental change. Scientists need to calibrate instruments, account for uncertainty, compare satellite data with ground measurements and combine observations with models. A change in a satellite image may raise a question, but further analysis is often needed to understand its cause.
The satellite's long record has made it useful for studying changes in the Earth system. Its mission also demonstrates how space technology can be applied directly to questions about the environment, climate and human activity.
Classroom connection: Using satellite data to study Earth
Terra offers a practical introduction to remote sensing and environmental data. Students can examine satellite images of vegetation, fires, clouds or land-use change and ask what the observations show. They can then distinguish between what is directly visible in the data and what requires further evidence or interpretation.
For example, if a satellite image shows a reduction in vegetation in a particular region, students could suggest possible explanations such as seasonal change, drought, fire or land clearing. They should also identify what additional information would help distinguish between those explanations.
This is an opportunity to practise scientific reasoning rather than simply identify features in an image. Students can discuss why scientists use repeated observations, why one image may be misleading and how data from different instruments can provide complementary evidence.
For older classes, Terra can also introduce the use of datasets in climate and environmental science. Students might compare measurements from different years, investigate a regional environmental trend or consider how scientists assess uncertainty when using remote observations.
If you are teaching space science alongside planetary environments, my space exploration reading comprehension passage and questions provides another way for students to explore the technology and science involved in investigating space.
Bring science history into your classroom
Project SCORE, J. J. Thomson's experiments and the launch of Terra all show how scientific instruments change what people can do and what they can know. A communications satellite extends the reach of a signal. An experiment with cathode rays reveals evidence of particles inside atoms. An Earth-observation satellite collects measurements across the planet that help scientists study environmental processes.
These stories can be used as short lesson starters, discussion prompts or introductions to a longer topic. Students could compare the purpose of each instrument, the information it collects and the scientific or technological question it helps answer. They could also discuss the limitations of each system: a satellite has finite power and operating life, an experiment depends on the quality of its measurements, and an Earth-observation instrument cannot explain every environmental pattern by itself.
My December Science on This Day resource set makes it easier to build these connections into lessons throughout the month. It includes 132 STEM events across December, with an interactive HTML resource for browsing and selecting events, editable slides with classroom discussion questions, a spreadsheet and a printable PDF. Teachers can use one event as a quick warm-up or select a date that connects directly to a topic they are teaching.
What else happened in science during December?
December's remaining dates offer further opportunities to connect science history with the curriculum. On December 20, the Experimental Breeder Reactor I in Idaho produced electricity from nuclear energy in 1951, providing a follow-up to the science of nuclear fission and a useful starting point for discussing how nuclear reactions can be used to generate electricity.
On December 21, Apollo 8 launched on the first crewed mission to orbit the Moon. The mission offers opportunities to discuss orbital motion, navigation and the challenges of sending astronauts beyond low Earth orbit. The crew's famous Earthrise photograph also provides a starting point for considering how observations from space can change our perspective on Earth.
On December 24, the Apollo 8 Earthrise photograph, taken during the mission in 1968, can be used to discuss the relationship between observation, photography and our understanding of the planet. It is a useful reminder that scientific instruments can provide evidence as well as new perspectives.
On December 25, 2021, the James Webb Space Telescope launched on a mission to study the Universe in infrared light. Its instruments allow astronomers to investigate distant galaxies, stars and planetary systems, making it a useful connection to light, telescopes and the challenges of observing objects across enormous distances.
From the first communications satellite to the discovery of the electron and the long-term observation of Earth, December 18 highlights how scientific tools extend human understanding. These events help students see science as a process of building instruments, collecting evidence and using that evidence to explain the world around them.
Thanks for reading
Cheers and stay curious
Oliver - The Teaching Astrophysicist
