TLDR: Ten observational-cosmology firsts have been added to PlayMemorize’s history dataset, filling the century between Hubble’s 1929 expansion result and the present. The new rows are Henrietta Leavitt’s period-luminosity relation (1912), Cecilia Payne-Gaposchkin showing stars are mostly hydrogen (1925), Karl Jansky detecting cosmic radio waves (1932), Penzias and Wilson finding the cosmic microwave background (1965), Vera Rubin’s galaxy rotation curves and dark matter (1978), the launch of the Hubble Space Telescope (1990), the first exoplanet around a sun-like star (Mayor and Queloz, 51 Pegasi b, 1995), the discovery of accelerating expansion / dark energy (Perlmutter, Riess, Schmidt, 1998), the first direct gravitational-wave detection by LIGO (2015), and the first image of a black hole by the Event Horizon Telescope (M87*, 2019). Together they take cosmology in When Did, Who Did, and Order by When from one anchor (Hubble 1929) to eleven.
The ten events covered below are the new dates that surface when you ask who first measured the size of the universe?, when was the cosmic microwave background discovered?, or in what order did these cosmology firsts happen?. Each entry is a single, citable publication or detection year tied to a named scientist (or a small named team) where one exists, plus three collaboration-actors for the detections that were genuinely pulled off by hundreds of co-authors. All ten are now rows in the shared historical-events-data.ts file, so the three history games pick them up automatically.
Why these ten?
The selection rule is the same one used for the recent crewed-spaceflight expansion: each event has to be a first that nobody can take away. “First period-luminosity calibration of variable stars” is a first; “most precise measurement of the Hubble constant” is a record that gets broken every few years. “First direct gravitational-wave detection” is a first; “loudest gravitational-wave detection” is trivia. Every event below also satisfies a second test: a single, agreed publication or detection year, with the discovery paper or detection event as the canonical date. Where the press release lagged the detection by months (CMB, GW150914, M87*), the year is the year of the detection, not the announcement.
One row from this arc was already in the dataset before this expansion landed: Expanding universe evidence published (Hubble, 1929). The ten new rows extend that anchor in both directions, picking up Leavitt’s distance ladder seventeen years earlier and continuing through the cosmic microwave background, dark matter, the first exoplanet, dark energy, gravitational waves, and the first picture of a black hole’s shadow.
1912 · Cepheid period-luminosity relation
In 1912, Henrietta Swan Leavitt published a short note in the Harvard College Observatory Circular reporting that the brightness cycles of 25 Cepheid variable stars in the Small Magellanic Cloud followed a clean linear relation between their pulsation period and their average luminosity. Because all 25 stars were at roughly the same distance from Earth, any difference in their apparent brightness had to reflect a real difference in the light they put out. Calibrating one nearby Cepheid then turned every other Cepheid in the sky into a standard candle. Hubble’s 1929 expansion result, the first reliable distance to the Andromeda galaxy, and every modern measurement of the Hubble constant ride on Leavitt’s relation.
Leavitt and Hubble are an “if-then” pair. If the era pool surfaces both henrietta-leavitt and edwin-hubble at the higher difficulties of Who Did, the rule is who measured what: Leavitt calibrated the standard candle (1912), Hubble used the candle to measure the recession of galaxies (1929). The 17-year gap is one of the cleanest causal chains in 20th-century science.
1925 · Stars are made of hydrogen
Cecilia Payne-Gaposchkin’s Radcliffe doctoral thesis, Stellar Atmospheres, argued that the apparent uniformity of stellar spectra was an artifact of ionisation rather than composition, and that stars were in fact made overwhelmingly of hydrogen and helium. Her thesis advisor, Henry Norris Russell, talked her into hedging the conclusion as “almost certainly not real” before publication; he changed his mind four years later and the result is now standard. The thesis is sometimes called the most brilliant ever written in astronomy.
The discovery year stored in PlayMemorize is 1925 · the year of the thesis defence and the published version. If the distractor set in When Did hugs that year (1924, 1925, 1926, 1927), the anchor is “the same year the General Strike was being planned in Britain and the year before Eisenstein’s Battleship Potemkin”. Stars-are-hydrogen is a 1925 result.
1932 · Cosmic radio waves detected
Karl Jansky was a 26-year-old Bell Telephone Laboratories engineer assigned to find the static interfering with transatlantic radiotelephone calls. He built a 100-foot rotating antenna in a New Jersey field, traced the loudest part of the static to a fixed point in the constellation Sagittarius, and published the result in 1933. The point turned out to be the centre of the Milky Way, and Jansky had accidentally founded radio astronomy. He never followed it up · Bell Labs reassigned him to other projects · but the unit of radio flux density is now the jansky.
Two famous “1932 cosmology” candidates exist. Jansky’s static traced to Sagittarius A is one of them. Carl Anderson’s discovery of the positron in cosmic-ray cloud-chamber tracks is the other. PlayMemorize stores Jansky for 1932; if you see karl-jansky in Who Did against an event labelled “Cosmic radio waves detected” the answer is unambiguous, but in mixed-difficulty Order by When draws the two 1932 firsts can sit a few rows apart.
1965 · Cosmic microwave background
Arno Penzias and Robert Wilson, Bell Labs engineers like Jansky three decades earlier, were calibrating a horn antenna in Holmdel, New Jersey when they hit a uniform 3.5-Kelvin hiss they could not explain. They cleaned the antenna, evicted a roosting pair of pigeons, and still could not get rid of the signal. A phone call to Robert Dicke at Princeton in early 1965 produced the punchline: Dicke’s group had been preparing to look for exactly that signal as the relic radiation of the Big Bang. The two papers ran back to back in The Astrophysical Journal Letters later that year. Penzias and Wilson shared the 1978 Nobel Prize in Physics.
1965 is now a triple-anchor year. PlayMemorize already stored Alexei Leonov’s first spacewalk (March 1965). The cosmic microwave background detection paper is from the same calendar year. Both rows live in the dataset under different topics · Leonov is exploration, Penzias and Wilson are science · so a topic-filtered draw will only ever surface one of the two, but a 5-event “all topics” Order by When can put both 1965 entries on the same screen.
1978 · Galaxy rotation curves and dark matter
Vera Rubin, working with Kent Ford at the Carnegie Institution, used a high-resolution image-tube spectrograph to measure the rotation of stars in spiral galaxies as a function of distance from the centre. The flat rotation curves she published in 1978 (and, in the longer collaboration, into the early 1980s) showed that the outer stars of a galaxy circulate at the same speed as the inner stars · which is impossible if the galaxy’s mass is concentrated where the visible light is. Either Newton’s law of gravity is wrong on galactic scales, or there is far more matter in galaxies than the stars and gas we can see. Forty-eight years later, the dark-matter explanation is the consensus, and Rubin’s curves are the canonical evidence.
Rubin is the easiest “she” trap in the dataset. The other women in the cosmology arc · Leavitt, Payne-Gaposchkin, and (joining the catalog at the same time as this expansion) the LIGO and EHT collaborations · all sit far away from 1978. If the era pool at high difficulty surfaces a same-decade female actor as a distractor, it will be Sally Ride or Tereshkova, both spaceflight rather than science. The cosmology distractor pool around 1978 is mostly Voyager (1977) and Apple (1976), neither of which is plausible for a paper on galactic rotation.
1990 · Hubble Space Telescope launched
The Hubble Space Telescope rode to orbit on Space Shuttle Discovery’s STS-31 mission on 24 April 1990 and was deployed the next day. Its 2.4-metre primary mirror had been ground to the wrong shape · the spherical aberration was off by 2.2 micrometres at the edge · and the first images came back blurry. Three and a half years later, STS-61 fitted COSTAR (a corrective optics package) and the Wide Field Planetary Camera 2, and Hubble began producing the images it is now famous for. Five servicing missions over 19 years kept it operating; the final servicing in 2009 left it expected to last into the 2030s.
The actor field stores “NASA”, consistent with voyager-launch (1977) and james-webb-launch (2021). All three are crewed-or-uncrewed launches by the same agency on a common timeline · NASA at 1977, 1990, and 2021. In Who Did’s era pool at high difficulty, NASA can show up as the correct answer for any of the three; the way to disambiguate is by the launch year in the prompt label, not by the actor.
1995 · First exoplanet around a sun-like star
On 6 October 1995, Michel Mayor and Didier Queloz of the Observatoire de Genève announced the discovery of 51 Pegasi b, a Jupiter-mass planet on a 4.2-day orbit around a sun-like star 50 light-years away. The detection was made by the radial-velocity method · watching the host star wobble toward and away from Earth as the planet’s gravity tugged it · using a spectrograph at the Observatoire de Haute-Provence in southern France. The discovery was independently confirmed within a week by Geoffrey Marcy and Paul Butler. Mayor and Queloz shared the 2019 Nobel Prize in Physics.
The 1992 pulsar planets are an honest distractor. Aleksander Wolszczan and Dale Frail published two planetary-mass companions to the millisecond pulsar PSR B1257+12 in 1992 · three years before 51 Peg b · and they are technically the first confirmed exoplanets. PlayMemorize’s row is specifically around a sun-like star; the pulsar planets orbit a stellar corpse and live in a different category of detection. If When Did offers 1992 as a distractor against the sun-like-star prompt, 1992 is wrong.
1998 · Accelerating expansion of the universe
Two independent teams · Saul Perlmutter’s Supernova Cosmology Project and the High-Z Supernova Search Team led by Brian Schmidt and Adam Riess · measured the recession velocities of distant Type Ia supernovae and found, to their collective surprise, that the universe’s expansion is not slowing down under gravity but speeding up. The Riess et al. paper appeared in September 1998; the Perlmutter et al. paper followed in 1999. Both teams were jointly awarded the 2011 Nobel Prize in Physics. The cause of the acceleration · “dark energy” · accounts for roughly 68% of the present-day energy budget of the universe and is, twenty-eight years later, still mostly mysterious.
Three names share one actor row. The actor stored in the dataset is perlmutter-riess-schmidt, displayed as “Perlmutter, Riess, and Schmidt”. This follows the existing “Watson and Crick” / “Hillary and Norgay” / “Doudna and Charpentier” pattern · a small named team gets one combined actor entry rather than one per person. The two 2012 rows (CRISPR and Higgs) work the same way. If Who Did at high difficulty draws Mayor and Queloz (1995) into the same era pool, the rule is which paper · planet around a sun-like star is the two-name entry, accelerating expansion is the three-name one.
2015 · First direct detection of gravitational waves
At 09:50:45 UTC on 14 September 2015, the two LIGO detectors at Hanford, Washington and Livingston, Louisiana recorded a 0.2-second chirp from the merger of two black holes about 1.3 billion light-years away. The signal · catalogued as GW150914 · matched general-relativity templates within a fraction of a percent and confirmed both the existence of black-hole binaries and the existence of gravitational waves a hundred years after Einstein had predicted them. The collaboration sat on the result for five months while it was independently re-checked, then announced it on 11 February 2016. Rainer Weiss, Barry Barish, and Kip Thorne shared the 2017 Nobel Prize in Physics for their roles in building LIGO.
The detection year is 2015, not 2016. A common trap in When Did is to confuse the announcement year with the detection year. PlayMemorize stores 2015 because that is when the wave passed through the Earth · the announcement is press-release timing. The same convention applies to the cosmic microwave background (detection 1964 · 1965, announcement 1965) and the M87* image (observation 2017, announcement 2019, where 2019 is what the dataset stores because 2017 was a long observing campaign).
2019 · First image of a black hole
The Event Horizon Telescope · a planet-spanning array of eight radio telescopes synthesised into one Earth-sized virtual antenna using very long baseline interferometry · released the first resolved image of a black hole’s shadow on 10 April 2019. The target was M87*, the supermassive black hole at the centre of the elliptical galaxy Messier 87, 55 million light-years away and roughly 6.5 billion times the mass of the Sun. The image · a bright orange ring around a dark central spot · is the projection of the photon orbit just outside the event horizon. A second image, of Sagittarius A* at the centre of our own galaxy, followed in 2022; PlayMemorize stores only the first.
The actor is the collaboration, not Katie Bouman. The young computer scientist whose photograph went viral alongside the M87* image was one of more than 200 co-authors and the lead developer of one of three independent imaging algorithms used to process the EHT data. The result is genuinely a collaboration achievement, and PlayMemorize attributes it to eht-collab · “the Event Horizon Telescope collaboration” · in the same way that the LIGO row is attributed to ligo-collab and the 2012 Higgs row is attributed to cern · “CERN scientists”. A four-way pool that mixes a collaboration name with named astronomers will sit comfortably alongside any of those three.
How to drill these in PlayMemorize
Open Order by When with topic set to Science & invention and count set to 8 and the modern-cosmology arc becomes a single eight-card challenge: 1912 (Leavitt), 1925 (Payne-Gaposchkin), 1929 (Hubble · already in the dataset), 1932 (Jansky), 1965 (Penzias and Wilson), 1978 (Rubin), 1995 (Mayor and Queloz), 1998 (dark energy). Add the count to 10 and the 2012 Higgs row plus the 2015 LIGO chirp slot in at the right edge. The two clusters worth memorising are the 1912 → 1932 trio (Cepheids · hydrogen · radio) and the 1965 → 1978 pair (CMB · dark matter); the rest of the rows fall into place as solitary anchors at 1995, 1998, 2012, 2015, and 2019.
Anchor the dates by Nobel year, not by paper year. Several of the new rows have a famous Nobel year that is decades downstream of the actual discovery. Penzias and Wilson detected the CMB in 1964 · 1965, Nobel 1978. Mayor and Queloz published 51 Peg b in 1995, Nobel 2019 (the same year as the M87* image). Perlmutter, Riess, and Schmidt published in 1998, Nobel 2011. PlayMemorize stores the discovery year because that is the citable scientific event; the Nobel year is what you will remember from news coverage. If a distractor in When Did hugs the Nobel year instead of the discovery year, the Nobel year is wrong.
Topic filtering keeps the focus tight. The history dataset now spans roughly 100 events from 1754 BCE (Code of Hammurabi) to 2021 (James Webb). Setting topic to Science & invention filters the pool to the rows about discoveries, theories, and inventions · including nine of the ten new ones (Hubble Space Telescope is filed under Exploration to match Voyager and James Webb). That is the smallest pool that still carries every named cosmology actor, and it isolates the discovery arc cleanly from the polar exploration and crewed-spaceflight arcs that share the same century.
These ten rows do not replace the existing astronomy entries in historical-events-data.ts. They expand them, taking the cosmology footprint from one anchor (Hubble 1929) to eleven, end to end from Henrietta Leavitt’s 1912 yardstick to the first image of a black hole’s shadow.
Christoffer De Geer
