- What later technologies and phenomena trace their understanding back to this mass-energy equivalence?
Stellar Astrophysics
The structure, evolution, and death of stars.
- How can two stars share the same colour but differ enormously in luminosity?
- What did Hertzsprung's distinction between giant and dwarf stars imply about their evolutionary histories?
- What is the Hertzsprung-Russell diagram, and what does it show about most stars?
- How can astronomers use a star's position on the Hertzsprung-Russell diagram to read its life stage?
- What pattern did Leavitt notice between a Cepheid variable star's period and its brightness?
- Why did the stars in the Small Magellanic Cloud provide Leavitt with a reliable way to compare absolute stellar brightness?
- What job did Henrietta Swan Leavitt hold at the Harvard College Observatory, and how did it shape her discovery?
- How did Leavitt's period-luminosity relation later enable Edwin Hubble to measure the scale of the universe?
- How does the period-luminosity relationship of Cepheid variables let astronomers measure cosmic distances?
- What did Harlow Shapley find when he analysed the spectral lines of Cepheid variables through their pulsation cycles?
- How did Shapley's finding rule out the possibility that Cepheid brightness changes were caused by an eclipsing companion star?
- Why did confirming a physical pulsation mechanism matter for trusting the period-luminosity relationship as a cosmic distance ladder?
- How did Shapley later use Cepheid distances to argue that the Sun sits far from the center of the Milky Way?
- How did Edward Emerson Barnard detect the star's motion by comparing photographic plates taken years apart?
- Why does Barnard's Star have the largest proper motion of any known star, and what does that reveal about its distance from Earth?
- Why is Barnard's Star, despite being so close, too faint to see without a telescope?
- How did Harlow Shapley use Cepheid variable stars to measure distances to globular clusters?
- Why is the relationship between a Cepheid's pulsation period and its luminosity useful as a cosmic distance ruler?
- How bright did Nova Aquila 1918 become, and how did that compare to previous novae like Kepler's star?
- What did spectroscopic study of Nova Aquila's dimming reveal about the expanding shell of gas?
- What modern explanation for novae — involving a white dwarf and a companion star — replaced the 1918 understanding?
- How did Michelson and Pease use a 20-foot steel beam on the Mount Wilson telescope to measure a star's diameter?
- What angular diameter did Michelson and Pease measure for Betelgeuse, and how did that translate into a physical size?
- How large would Betelgeuse's diameter be relative to the orbits of the inner planets if placed at the Sun's position?
- What is the period-luminosity relation Henrietta Swan Leavitt discovered in Cepheid variable stars?
- How did Edwin Hubble use Leavitt's relation to prove the Andromeda nebula lay outside the Milky Way?
- Why was Leavitt classified as a 'human computer' rather than a scientist during her career at Harvard?
- Why was Leavitt never awarded a Nobel Prize despite being nominated after her death?
- How do Cepheid variable stars let astronomers measure distances to other galaxies?
- What method did Cecilia Payne use to determine the composition of stars from their spectra?
- What had astronomers previously assumed stars were made of, before Payne's thesis?
- Why did Henry Norris Russell pressure Payne to downplay her own finding, and what happened when he later confirmed it himself?
- How did Cecilia Payne's spectroscopic analysis show that stars are made overwhelmingly of hydrogen?
- Why did Henry Norris Russell initially pressure Payne to disavow her own correct conclusion?
- How did the discovery of hydrogen's dominance in stars explain how stars generate energy?
- What does this episode reveal about how credentialed scepticism can delay scientific recognition?
- Why did gravitational contraction fail as an explanation for how long the Sun could keep shining?
- What are the proton-proton chain and the carbon-nitrogen-oxygen cycle, and which stars rely on each?
- How did geologists' evidence for Earth's true age create a problem for existing theories of solar power?
- Why did Bethe's Nobel recognition come nearly three decades after the actual calculations?
- How did astronomers use a stellar occultation to detect rings around Uranus that no one had ever seen directly?
- Why did the star's light blink out multiple times both before and after Uranus passed in front of it?
- What is the Chandrasekhar limit, and why can't a white dwarf above roughly 1.4 solar masses hold itself together?
- How did William Fowler's nuclear physics work explain where elements heavier than hydrogen come from?
- Why is the observatory named after Subrahmanyan Chandrasekhar?
- What did Fred Hoyle's B2FH paper explain about how stars forge the elements heavier than helium?
- What process did Hans Bethe identify as the mechanism powering massive stars?
- What role did Bethe play at Los Alamos during the Manhattan Project?
- How did Bethe's later stance on nuclear weapons and missile defence relate to his wartime work?
- What personal connections did Bethe have to both Einstein and Oppenheimer?
- Why do Proxima Centauri's ultraviolet flares pose a challenge to any atmosphere the planet might have?
- What makes TRAPPIST-1 an unusual host star for a planetary system, given how dim and small it is?
- How did Genzel and Ghez track individual stars to prove something massive and invisible sits at the centre of the Milky Way?
- How did Venus flybys let the Parker Solar Probe shrink its orbit close enough to reach the Sun?
- How did Gaia use the method of parallax to measure the precise distances to nearly two billion stars?