Science on This Day: November 24 | The Transit of Venus, Darwin’s Evolution and Apollo 12
November 24, 1639: A rare planetary alignment helps astronomy advance
On November 24, 1639, English astronomer Jeremiah Horrocks and his friend William Crabtree made the first known successful observations of a transit of Venus across the Sun. Horrocks had predicted the event using his calculations of planetary motion. It was a remarkable achievement because transits of Venus are rare, and observing one required careful preparation, accurate timing and suitable viewing conditions.
A transit occurs when a planet passes directly between Earth and the Sun, appearing as a small dark spot moving across the Sun’s bright disc. From Earth, only Mercury and Venus can transit the Sun because they orbit closer to the Sun than we do. Even then, the planets' orbits are tilted relative to Earth's orbital plane, so a transit does not happen every time a planet passes between Earth and the Sun.
Horrocks used a telescope and a safe projection method to observe the event. Rather than looking directly at the Sun through a telescope, an observer can project the Sun's image onto a surface and watch the small silhouette of Venus move across it. This makes the transit easier to study while avoiding the serious risk of eye injury from direct solar viewing.
The importance of transits extends beyond their rarity. In later centuries, astronomers used observations of Venus transits from widely separated locations on Earth to help estimate the distance between Earth and the Sun. By comparing the apparent path and timing of Venus from different places, scientists could use geometry to calculate the scale of the Solar System. The Royal Museums Greenwich guide to transits of Venus explains the history and astronomical importance of these observations.
Bring this into the classroom
A transit of Venus is a useful way to introduce orbital motion, the geometry of the Solar System and the difference between a planet's orbit and the view we see from Earth.
Students can model the Sun, Earth and Venus using three objects, then change the angle of Venus's orbital path to explore why transits do not occur every time Venus passes between Earth and the Sun.
Ask students: How can a transit be used to estimate the distance between Earth and the Sun?
For older students, the discussion can lead into parallax and triangulation. If two observers see Venus against slightly different positions on the Sun's disc, their observations can be combined with knowledge of the distance between their observing locations. This provides a route into the geometry used to estimate astronomical distances.
It is also a chance to discuss the limits of observation. A transit is an observable event, but turning that observation into a measurement of the Solar System requires accurate timing, suitable instruments, a reliable model and observations from different locations.
Never ask students to look directly at the Sun through a telescope, binoculars or an unfiltered camera. A projection activity or suitable specialist solar-viewing equipment is essential for safe observation.
November 24, 1859: Charles Darwin publishes On the Origin of Species
On November 24, 1859, Charles Darwin published On the Origin of Species, a book that became one of the most influential works in the history of biology. Darwin presented evidence and arguments for evolution by natural selection, helping establish a scientific explanation for how populations change over generations and how species become adapted to their environments.
Darwin had spent years collecting observations and considering how species vary. His work was influenced by evidence from many sources, including fossils, geographical distributions, domesticated plants and animals, and the similarities and differences between living organisms. These observations helped him develop an explanation for how populations could change over time.
Natural selection is based on several connected ideas. Individuals within a population vary. Some of those differences can be inherited. More offspring are often produced than can survive and reproduce, so individuals face competition and other environmental pressures. If an inherited characteristic helps an organism survive and reproduce in a particular environment, that characteristic may become more common in later generations.
For example, imagine a population of insects living on dark tree bark. If some insects have darker colouring and are less easily seen by predators, they may be more likely to survive and reproduce. Over many generations, darker colouring could become more common in that population, provided the relevant variation is inherited and the environmental conditions favour it.
Natural selection does not mean that organisms consciously change because they need to, or that evolution always produces more complex or supposedly better organisms. Instead, the characteristics that become more common depend on the environment and on which individuals leave more surviving offspring. A characteristic that is useful in one environment may be less useful in another.
Darwin's book did not settle every question about evolution. Genetics was not yet understood in the modern sense, and scientists continued to investigate how variation is inherited. Later discoveries, including the development of genetics and the study of DNA, added important explanations to the theory of evolution. The original text of On the Origin of Species is available through Darwin Online.
Bring this into the classroom
Darwin's work is ideal for teaching adaptation, variation, inheritance, natural selection and the nature of scientific evidence. Students can examine a simple example of natural selection, identify the variation within a population, explain the environmental pressure and predict how the population might change over several generations.
A useful question is: What kinds of evidence can support a scientific explanation for biological diversity?
Students might compare fossil evidence, anatomical similarities, geographical distribution and genetic evidence. Ask them what each type of evidence can tell us, and what its limitations might be. This helps them understand that a strong scientific explanation is supported by multiple lines of evidence rather than a single observation.
The history also gives teachers an opportunity to distinguish between a scientific theory and an everyday guess. In science, a theory is a broad explanation supported by evidence and capable of being tested against observations. Evolution is supported by many independent lines of evidence, and scientific research continues to refine our understanding of how evolutionary processes operate.
For a short activity, give students a set of observations about a population and ask them to develop an explanation for a change across generations. They should identify which parts of their explanation are supported by evidence and which would require further investigation. This can build scientific reasoning without requiring students to memorise the details of Darwin's life.
November 24, 1969: Apollo 12 returns from the Moon
On November 24, 1969, Apollo 12 splashed down in the Pacific Ocean, returning astronauts Charles “Pete” Conrad, Alan Bean and Richard Gordon safely to Earth. The mission was NASA's second crewed lunar landing. Conrad and Bean had landed on the Moon on November 19, while Gordon remained in lunar orbit aboard the command module.
Apollo 12 was important not only because astronauts reached the Moon again, but because the mission demonstrated that a lunar landing could be carried out with greater precision. The crew landed near the robotic Surveyor 3 spacecraft, which had reached the Moon in 1967. Conrad and Bean inspected the Surveyor craft and brought selected parts back to Earth, allowing scientists to examine how materials and equipment had been affected by prolonged exposure to the lunar environment.
The mission also returned lunar rocks and soil for analysis. Samples brought back from the Moon can be studied with instruments that are too large, delicate or complex to send into space. Scientists can measure their chemical composition, examine their minerals and compare them with samples from Earth and meteorites. These investigations help answer questions about the Moon's formation, its geological history and the processes that have shaped its surface.
Apollo 12's launch had also presented a serious challenge. Lightning struck the Saturn V rocket shortly after liftoff, disrupting spacecraft electrical systems and telemetry. Flight controller John Aaron recognised an unusual pattern in the spacecraft data and recommended a switch configuration that helped restore the systems. The mission continued successfully, demonstrating the importance of trained teams, clear communication and the ability to respond to unexpected problems.
The splashdown marked the end of a mission, but not the end of the science. Returning the astronauts, equipment and lunar samples to Earth allowed further analysis and helped researchers learn from the mission. NASA's Apollo 12 mission history provides further details about the landing, the samples and the spacecraft.
Bring this into the classroom
Apollo 12 offers a strong connection to space science, engineering, materials science and experimental design. Students can compare a robotic mission with a crewed mission and consider what each can do well. Robots can operate in environments that are dangerous for people, while astronauts can make decisions and adapt to unexpected situations, although crewed missions carry additional risks and costs.
Ask students: What scientific value came from bringing lunar samples and spacecraft parts back to Earth?
They could plan an investigation into a lunar rock sample, identifying the measurements they would make and the questions each measurement could answer. Alternatively, they could investigate why engineers test equipment before a mission and how a failure early in a flight might affect the rest of the mission.
Apollo 12 is also a useful example of the relationship between technology and scientific knowledge. A successful landing was an engineering achievement, but it enabled scientists to collect evidence that could not be obtained in the same way from Earth. The spacecraft was both a vehicle and a scientific tool.
Using Science on This Day as a classroom activity
These three events offer very different entry points into science lessons. The transit of Venus connects astronomy with geometry and observation. Darwin's publication connects biology with evidence, variation and natural selection. Apollo 12 brings together engineering, geology, physics and scientific investigation.
You could use one event as a five-minute starter, asking students to explain the key scientific idea in their own words. Alternatively, students could choose one event and identify the question scientists were trying to answer, the evidence they used and what further research became possible.
My November Science on This Day activity set contains 109 STEM stories across November, designed to help teachers bring science history into everyday lessons. It includes an interactive HTML version, editable Google Slides, a filterable spreadsheet and a PDF version. You can choose an event by date or subject, use the classroom display mode, and use the included discussion questions to prompt students to explain, compare and evaluate ideas.
If you are looking for a way to try science-history starters with your classes, you can also explore the free and paid resources in The Teaching Astrophysicist store. There are resources across physics, biology, chemistry, Earth science and space, with different formats to suit a range of classroom activities.
What else happened around November 24?
November 25 offers three more useful connections to science. The Great Storm of 1703 provides a case study in severe weather, historical records and the difficulty of estimating the strength of a storm from accounts written before modern instruments were available. Julius Robert von Mayer, born on November 25, 1814, was an early contributor to the development of the principle of conservation of energy and the relationship between heat and mechanical work. On November 25, 1915, Albert Einstein presented the final field equations of general relativity, an important step in developing a new explanation of gravity.
On November 26, engineer Willis Carrier, born in 1876, is remembered for work that helped make modern air conditioning practical. This is a useful link to heat transfer, humidity and engineering design. The same date is associated with Howard Carter and his team's first view into the tomb of Tutankhamun in 1922, which can lead to a discussion of archaeology, preservation and the scientific methods used to study historical materials.
As the month draws to a close, you can continue with the December Science on This Day activity set. It contains 132 STEM stories across all 31 days of December, with several formats for selecting events, presenting them to a class and encouraging discussion.
The stories of November 24 remind us that scientific knowledge develops in different ways. Astronomers used a rare celestial event to improve measurements of the Solar System.
Darwin assembled observations into an explanation for biological diversity. Apollo 12 returned samples and equipment that scientists could examine in laboratories on Earth. Each story shows how observations become more useful when people ask questions, test explanations and build on evidence collected by others.
Thanks for reading
Cheers and stay curious
Oliver - The Teaching Astrophysicist
