What's new
Essays arrive in groups rather than one at a time, and a group usually opens up a subject not covered before. Between one group and the next nothing changes, so a reader who has seen the most recent group has seen everything.
2 November 2026
18 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
Cosmology
A clump that waits for the radiation to thin
Dark matter feels no pressure from light, so nothing should have stopped it clumping in the radiation era. Almost nothing did stop it, and yet a clump inside the horizon at that time barely grows. The radiation does not push on it. It only makes the universe expand too fast for the clump's own gravity to keep up — and the length of that wait is the bend in the spectrum of every structure in the sky.
Cosmology
A balance that is a saddle
In 1917 Einstein added a constant to his equations to hold the universe still, and the constant does exactly that: there is one size at which the attraction of matter and the repulsion of the constant cancel. Eddington showed in 1930 that the balance is a pencil on its point. A thousandth out and it is gone in seven units of its own free-fall time. The instability is not a flaw of that one model. It is why the real universe could cross the same balance without stopping.
Exoplanets
A moon read from how late and how long
A moon pulls its planet round their common centre, and at each transit the planet is somewhere slightly different along that small orbit, moving slightly differently. So the transit arrives early or late, and it lasts longer or shorter. The two effects depend on the moon in different ways and they run a quarter of a cycle apart. Neither alone says anything about the moon. Their ratio gives its period, which a series of transits sampled once an orbit cannot otherwise reach.
Exoplanets
Water that is on the star and not the planet
A transit depth is the planet's shadow divided by the brightness of the whole star, and the shadow falls on only one strip of it. If the strip is cleaner than the rest of the disc, the depth comes out too large, by an amount that changes with colour. The star's own spots hold water, so the error has water's fingerprint. On the smallest red dwarfs, whose rocky planets are the best targets there are, that false signal is larger than the real atmosphere being looked for.
Galaxies
A cooling flow that never arrives
The gas at the centre of a rich cluster radiates its heat in under a billion years, so it should be sinking inward and turning into stars at hundreds of solar masses a year. For two decades that was the accepted picture and it was treated as a measurement. Then X-ray spectra looked for the gas on its way down and found that it stops at a third of the temperature it began with, while the galaxy in the middle forms stars a hundred times too slowly. Something pays the radiative bill, and bubbles of the right size are visible in the X-ray images.
Galaxies
A galaxy that grows faster by eating small
Two equal elliptical galaxies merge and the result has twice the mass and twice the size. A galaxy that takes in the same mass as thirty small companions ends up nearly four times the size. The difference is one line of the virial theorem, in which companions bring mass without much energy, and it may answer a puzzle thrown up by the first deep infrared surveys: the most massive galaxies at redshift two are a fifth of the size of anything like them today.
Gravitation
A particle on a line that can spell any word
Two equal stars orbit each other, and a speck of dust moves up and down on the line through their centre, perpendicular to their orbit. It has one coordinate and cannot leave that line. In 1973 Jürgen Moser proved that for almost any list of whole numbers, as long as they are large enough, there is an orbit whose successive excursions last exactly that many periods of the stars. The list can be chosen at random, so the orbit can do anything a coin can.
Gravitation
A force that can hide at any one distance
The inverse-square law is tested by comparing the strength of gravity at two distances, and every instrument that does so is sensitive over about one decade of range. A Yukawa force with a range outside that decade is invisible to it: much shorter and it never reaches, much longer and it only rescales the constant. So testing the law is not one experiment made more precise but a chain of unrelated ones, from torsion pendulums to the orbits of planets, and the chain has weak links exactly where no pair of masses of the right size can be arranged.
Orbits
A term too small to keep that a denominator kept
Every planetary theory is an expansion, and the order of its terms is meant to say which can be dropped. In the 1770s the largest unexplained motion in the Solar System, Jupiter speeding up and Saturn slowing down by a degree over centuries, came from a term that the ordering called negligible. Five of Saturn's orbits nearly match two of Jupiter's, and that one near-match divides a tiny third-order coefficient twice by a tiny frequency. An integration of the three bodies shows the swap directly, and shows what Laplace saw: it reverses every nine centuries.
Orbits
A perigee that moved twice as fast as Newton
The Sun's tide on the Moon should turn the line of its perigee once in eighteen years. It takes less than nine. For sixty years that was the outstanding failure of the law of gravitation, and in 1747 Clairaut told the Paris Academy that the inverse-square law would have to be amended. Two years later he withdrew the remark. The law was right and the calculation was unfinished: the series for the perigee has a small parameter that is not small, and its second term is seventy per cent of its first.
The observed sky
A full Moon that stops rising later
The Moon rises about fifty minutes later each day. That number is an average that hardly any night obeys. At fifty-two degrees north, in late September, the full Moon rises only ten or twenty minutes later for several nights running, so that a bright Moon stands in the evening sky for most of a week, just when harvest once needed it. Nothing about the Moon changes. It is the angle at which its path meets the horizon, and that angle goes through its lowest value at one point of the ecliptic, which the autumn's full Moon happens to occupy.
The observed sky
A Moon lit by every sunset at once
With no air, the Moon would vanish inside the Earth's shadow. Instead it turns a dull copper, because the atmosphere bends sunlight round the planet, and what reaches the Moon has gone through a ring containing every sunrise and sunset on Earth at that moment. Each height in the air lights one place in the shadow, so the colour across the disc is a map of the atmosphere by altitude. It has sometimes been black, after the largest volcanoes, and that makes a century of eclipse records a measurement of the stratosphere older than any instrument sent up to sample it.
Spaceflight
A way home that needs no engine
A spacecraft can leave the Earth so that the Moon's gravity turns it round and sends it home with no further burn. Drawn in the frame that turns with the Moon the path is a figure of eight. It was flown to the Moon by every early Apollo mission for one reason: if the engine fails, the crew comes back. That safety is exquisitely narrow. A tenth of a metre a second at departure moves the perilune by tens of kilometres and the return by thousands, and the perilune it allows is not one that most landing sites can use.
Spaceflight
A timetable that orbits the Sun
Every trip to Mars leaves when the planets line up and accelerates everything it carries. Buzz Aldrin proposed in 1985 that there need be only one departure: a large ship on an orbit that returns to the Earth each synodic period, with crews riding small taxis out to catch it. The orbit almost exists without any propellant. It has a semi-major axis fixed by a single condition, an aphelion that passes Mars with nothing asked for, and one unavoidable bill: it must turn by about fifty degrees every twenty-six months, and the Earth can pay for all but seven of the eighty the turn requires.
Starlight
An ionised sphere that is a count of photons
A hot star sits in a cloud of hydrogen and ionises it, out to a radius, and there the ionisation stops within a tiny fraction of the distance. That edge was predicted in 1939 from a single count: every recombination uses up one photon, so the star can hold ionised only as many atoms as its light can pay for. By the equation that describes a stellar atmosphere at the same temperature, the same gas would hold ten orders of magnitude fewer neutral atoms than it does. In a nebula the temperature is not what decides the ionisation. A budget is.
Starlight
An element that was only empty space
In 1864 William Huggins turned a spectroscope on a planetary nebula and saw a bright green line that matched nothing on Earth. It was given a name, nebulium, and it was treated as a new element for sixty years, until the periodic table had no room left for it. In 1927 Ira Bowen showed it was ordinary oxygen, emitting by a route that collisions close long before any laboratory vacuum could reach it. The line was never forbidden. It simply needs about a minute of being left alone, and nothing on Earth gets that.
Stars
A binary that goes silent for an hour of period
Binaries of a white dwarf feeding off a small star can be found at almost any orbital period down to about eighty minutes, except between about two and three hours, where they are strikingly rare. They have not stopped existing there. They have stopped shining. The moment the donor loses its radiative core, the wind's magnetic brake appears to switch off. The star, swollen by the transfer it was being driven through, shrinks back inside its own Roche lobe, and the feeding stops. Only gravitational waves remain to close the orbit, and it takes them about half a billion years.
Stars
A spot whose missing heat goes nowhere
A sunspot blocks most of the energy trying to come up beneath it, and a large group visibly dims the whole Sun by a thousandth. Energy is conserved, so the blocked flux ought to come out somewhere else, and for a century observers looked for the bright ring around every spot. There is none to speak of. The heat has gone into the rest of the convection zone, spread so fast and so widely that the surface cannot notice, and it will stay there for longer than human history. For the time being the Sun simply is fainter, without any contradiction.
Before that
Everything published earlier, newest first. Titles only — the cards are on the full listing.
29 October 2026
18 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- A flow too quiet for the lumps it runs between — cosmology
- A clock that flickers without a tick — cosmology
- A planet read in the ashes of its star — exoplanets
- The stars that could catch the Earth in transit — exoplanets
- A lens counted instead of measured — galaxies
- A halo weighed by counting its oldest clusters — galaxies
- A moon the Earth does not hold — gravitation
- Pairs of stars too loosely bound to survive heavy dark matter — gravitation
- A moonlet that weighs a pile of rubble — orbits
- A shower that is a reading of an orbit — orbits
- A year kept by a star seen for one morning — the observed sky
- A Moon that rises further north than the Sun — the observed sky
- A tow with no rope — spaceflight
- A cable with a rocket equation of its own — spaceflight
- A wavelength coincidence that weighs a neutron star — starlight
- A polarisation that a round star cancels — starlight
- A wind that carries the ledger of its loops — stars
- A lifetime that stops getting shorter — stars
23 October 2026
18 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- A drift in the tilt that is the tilt squared — cosmology
- A ratio in which the galaxies cancel — cosmology
- A peak that should move with the star — exoplanets
- A transit that says which star it crossed — exoplanets
- A flare rate a hole cannot afford for long — galaxies
- A lifetime read from how gas and stars sit apart — galaxies
- A constant bounded by the oceans — gravitation
- The tide that holds up the deep ocean — gravitation
- What Jupiter kept of the Sun's siblings — orbits
- Two clocks in the dust of one collision — orbits
- A midplane that depends on how far it is averaged — the observed sky
- A Moon measured in banded iron — the observed sky
- A dodge made of air — spaceflight
- An orbit lost to a burn that did not fire — spaceflight
- A mean that a few per cent of strays can drag — starlight
- A diameter smaller than the fringes can see — starlight
- A metallicity term too small to close a gap — stars
- A nebula that cannot be beamed at — stars
21 October 2026
18 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- A twist that decides where the field ends — cosmology
- A field the galaxies cannot spread far enough — cosmology
- An envelope that boils down before the starlight strips it — exoplanets
- A neighbour an eccentric arrival cannot leave — exoplanets
- A falling polarisation and the angle that says why — galaxies
- A molecule that forms too slowly to wait for — galaxies
- A population that cannot share the cluster's temperature — gravitation
- Precessions bought one hertz at a time — gravitation
- A tilt built from a thousand near misses — orbits
- A clock checked by the craters it is making now — orbits
- A glow counted in square metres of sunlit metal — the observed sky
- A booster that flies home pays with the stage above it — spaceflight
- Two exponents a solar cycle cannot pull apart — the observed sky
- A turn that costs more when the shadow sits on the node — spaceflight
- A halo the telescope paints on every galaxy — starlight
- A hundred kelvin under every radius — starlight
- An expansion clock read from the stars' motions — stars
- A correction that grows as the fifth power of the frequency — stars
18 October 2026
18 essays on gravitation, orbits, the observed sky, spaceflight, starlight, stars, exoplanets, cosmology and galaxies
- A ring that is thinner from one side — gravitation
- A drag that stops where every orbit keeps time — gravitation
- A wall that leans towards the body that damps — orbits
- A family checked by a colour it was not chosen by — orbits
- A reflector built wrong so the light comes home — the observed sky
- A rhythm in the rock that measures the Moon — the observed sky
- A rendezvous paid for in air — spaceflight
- An arrival the Sun hands over — spaceflight
- A rotation found where the transform goes dark — starlight
- A periodogram shaped like a shadow — starlight
- A star that distils itself as it freezes — stars
- A scatter that points the way dust does — stars
- A clock that slows, or a star that falls — exoplanets
- A null that removes a model and not its family — cosmology
- A bound below the floor is not a mass — cosmology
- A target list that counts pairs twice — exoplanets
- A lag too short for the light — galaxies
- A stream that points the wrong way — galaxies
14 October 2026
18 essays on galaxies, cosmology, exoplanets, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- A spiral drawn by velocities alone — galaxies
- A galaxy born without a halo — galaxies
- A dimming short by what young stars repay — cosmology
- A hole too deep for the sky to have made — cosmology
- A zodi measured in heat and needed in light — exoplanets
- An envelope spent so an ocean could stay — exoplanets
- A rare event reached by cloning the near misses — gravitation
- A relaxation that stops before it is finished — gravitation
- A correction that tilts the arc it meant to aim — orbits
- A check that cannot see the clock — orbits
- A year that depends on the season counting it — the observed sky
- A polarisation capped by the light the planet catches — the observed sky
- A turn spread where the climb leaves room — spaceflight
- A height the map already knows — spaceflight
- A temperature read against the light's long tail — starlight
- Where a shrinking star stops boiling at its centre — starlight
- A turnover whose position is an age — stars
- Four clocks and the stars none of them reads — stars
11 October 2026
36 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- An echo heard only from the weakest fields — cosmology
- A conversion measured without an alignment — cosmology
- A fraction read in each channel's own units — exoplanets
- A helium line that weighs the star first — exoplanets
- A halo with too much slow gas for a disc — galaxies
- A stirring supernovae cannot pay for — galaxies
- A probability for a system with one future — gravitation
- A shell outside the stream turns nothing — gravitation
- A deficit the giants hold and Mercury could borrow — orbits
- A surface that slides before the body sheds — orbits
- A state the Moon had to jump to — the observed sky
- A shield that depends on what limits the leak — the observed sky
- A thruster that must arrive slow — spaceflight
- An aim bought with the last day of the approach — spaceflight
- A rotation measure the lobe writes on its own boundary — starlight
- A calibration chosen by the measurement it calibrates — starlight
- A Sun read through a shield that also changed — stars
- A dynamo that did not need the shear layer — stars
- A wave pulled ahead by particles that outran it — cosmology
- A depth that belongs to the fit as much as the sky — cosmology
- A shoreline measured in light already spent — exoplanets
- A second peak the errors have to let through — exoplanets
- The grains that glow and the grains that align — galaxies
- A disc weighed by how far its stars climb — galaxies
- A Love number measured at nuclear density — gravitation
- A migration timed by the planet and not the moon — gravitation
- An orbit seen at an angle keeps everything but its focus — orbits
- An answer from two bodies, flown through a flattened Earth — orbits
- The shadow that also switches off the satellites — the observed sky
- A schedule written by where the Sun is — the observed sky
- Four satellites in view, and which four — spaceflight
- A ring where nothing leaves and little shatters — spaceflight
- A polarisation measured faster than the air changes — starlight
- A profile that averages a decade of depth — starlight
- A limit written for free electrons — stars
- A star that has to make its own catalyst — stars
10 October 2026
18 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- A mass scale checked near and carried far — cosmology
- A void dated by the dwarfs that lit in time — cosmology
- The heaviest atom a hydrogen wind can lift — exoplanets
- A gap in eccentricity a density can only just see — exoplanets
- Motions across the sky measure the orbits first — galaxies
- One profile for a galaxy that has two — galaxies
- A chaotic orbit clings to the edge of order — gravitation
- A gap that counting can test and impostors can fill — gravitation
- A kick that writes over the record of the pulses — orbits
- A young surface dated by a handful of holes — orbits
- A twinkle that knows the high air and not the low — the observed sky
- Layers that keep the rhythm and lose the dates — the observed sky
- No single way to point a long burn — spaceflight
- A plane turned only where turning is cheap — spaceflight
- A spot a slow star hides inside its velocity — starlight
- A lobe that reads the time since it was stirred — starlight
- A rise a detector shrinks to a tilt — stars
- A lone star is dated only as it leaves — stars
9 October 2026
18 essays on cosmology, exoplanets, galaxies, gravitation, orbits, stars, spaceflight, starlight and the observed sky
- Every thawing field falls on one line — cosmology
- The growth that tells a substance from a law — cosmology
- The Earth-sized bin is where diluted planets land — exoplanets
- A cadence that finds a planet is not one that weighs it — exoplanets
- A dispersion that weighs the sheet only if the orbits are known — galaxies
- A hundred lenses and one assumption — galaxies
- The binaries a core keeps are spread evenly in energy — gravitation
- Ejected from a globular, merged in a nucleus — gravitation
- Jupiter keeps only the visitors already nearly bound — orbits
- The jet that pushes a comet also turns it — orbits
- A precession slowed by stars lying on their sides — stars
- A lever set by the dipole and not the field — stars
- A belt drained through its outer door — spaceflight
- A dropout that is only the field — spaceflight
- Two distances that must agree if light is conserved — starlight
- A floor the star sets for itself — starlight
- Two clouds that shine alike until the crescent — the observed sky
- A clock whose best interval is three years — the observed sky
8 October 2026
18 essays on galaxies, gravitation, orbits, cosmology, the observed sky, exoplanets, spaceflight, starlight and stars
- A temperature that belongs to none of the gas — galaxies
- An atomic ceiling set by the dust — galaxies
- A floor under the unseen companion — gravitation
- A black hole weighed by a wobble on the sky — gravitation
- A kick speed read off the slope of a histogram — orbits
- A collision moves the cloud's centre, and an explosion cannot — orbits
- A map of galaxies none of which was seen — cosmology
- A line from the wrong redshift lands at the wrong distance — cosmology
- A frame fixed before its centre was found — the observed sky
- An eclipse held in place to a millimetre — the observed sky
- More iron than the star could give — exoplanets
- A day side as hot as bare rock — exoplanets
- A climb out of the ecliptic paid for in orbits — spaceflight
- The one axis the field will not take — spaceflight
- A shared axis hides at the angle where it does no harm — starlight
- The cancellation that leaves with the hot stars — starlight
- A field that waits for the core to freeze — stars
- Too large and too cool by just enough to keep the light — stars
7 October 2026
18 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- An alignment a disc shows only when it is tipped — cosmology
- A cluster weighed against the background behind it — cosmology
- A spread the projection does not hide — exoplanets
- A transit that runs differently backwards — exoplanets
- One slope read twice, and the reading that disagrees — galaxies
- A positron that cannot have come far — galaxies
- A few thousand clouds outrun a hundred billion stars — gravitation
- Torques that add because the orbits hold still — gravitation
- A distant planet felt only as a stretch — orbits
- A Moon that would lean towards the Sun — orbits
- A storm weighed by a compass needle — the observed sky
- A planet that borrows the wind's field — the observed sky
- A burn that cannot happen at one point — spaceflight
- Two metres overhead and thirty at the horizon — spaceflight
- A line darker than any temperature in the gas — starlight
- A width that knows how bright the star is — starlight
- A star tipped over at a thousand times its horizon — stars
- A soft centre the rest of the core outvotes — stars
5 October 2026
20 essays on stars, gravitation, orbits, the observed sky, spaceflight, galaxies, exoplanets, cosmology and starlight
- Mass that leaves takes the orbit's spin with it — stars
- A donor that grows as it is eaten — stars
- The least known number in binary evolution — stars
- A field the turbulence will not let in — gravitation
- A disc that stores its inflow and spends it in a century — gravitation
- A tilt the Moon should not have — orbits
- Four numbers that carry a state without an orbit — orbits
- A month that begins when someone sees it — the observed sky
- A day longer than the year — the observed sky
- A trajectory with no good first guess — spaceflight
- A removal rate set by one percentage — spaceflight
- A history the rotation curve absorbs — galaxies
- A cusp a black hole would sharpen — galaxies
- Water that remembers how cold it was — exoplanets
- A core that shut the door on the pebbles — exoplanets
- A void heated from the inside — cosmology
- An edge that needs no pulsation — cosmology
- Two clocks for one lobe — starlight
- A wind that may be too hot to see — starlight
- Light that adds, corrected as if it multiplied — starlight
2 October 2026
19 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- Polarised only where the glow was lopsided — cosmology
- A speed read from the finest spots in the map — cosmology
- A model of the star that can carry the planet — exoplanets
- A planet has one velocity in every colour — exoplanets
- A slope that is a whole curve of companions — exoplanets
- A black hole thrown out by its own merger — galaxies
- The black holes that can be weighed are the heavy ones — galaxies
- The one radius where the orbits stop mattering — galaxies
- A tide table is astronomy with the harbour fitted — gravitation
- A mountain's gravity says what holds it up — gravitation
- A slow shock heats the halo and robs the core — gravitation
- A fall is half an orbit with no width — orbits
- A census of visitors is a census of the survey — orbits
- Every star in the catalogue is bent by the Sun — the observed sky
- The Sun is three hundred kilometres larger seen edge-on — the observed sky
- A plane change borrowed from the Moon — spaceflight
- The thrust that rounds an orbit turns once a revolution — spaceflight
- A baseline that grows four astronomical units a year — starlight
- Brighter for its mass and fainter for its colour — stars
29 September 2026
20 essays on cosmology, orbits, the observed sky, spaceflight, starlight, gravitation, galaxies, exoplanets and stars
- Velocities that see past the edge of the map — cosmology
- A void is not short of dwarf haloes — cosmology
- A flatness that needs a second distance — cosmology
- The size forgets how the mass was lost, and the shape does not — orbits
- Eleven in a hundred by geometry, and the rest by waiting — orbits
- An ice sheet that skips a beat of the tilt — orbits
- Luck that reaches as far as the quiet air — the observed sky
- A sunset's shape is a sounding of the air — the observed sky
- The night is late because the light bounces twice — the observed sky
- A flyby that multiplies its own aiming error — spaceflight
- A grapple point that moves faster than the orbit — spaceflight
- The wall sells inclination at the dearest price — spaceflight
- The lines a synthesis keeps pay for the ones it lacks — starlight
- A glow that weighs the grains reddening cannot see — starlight
- A prior the survey measures through its own noise — starlight
- The shell can be flattened if it thins at the poles — gravitation
- The bar leaves its gas where the orbits turn — galaxies
- Every planet of a star must agree on its density — exoplanets
- Mechanics sets a star's temperature before fusion does — stars
- The pulse that shows the back of the star — stars
27 September 2026
20 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- A background that stops breaking into sources — cosmology
- The histogram of a sky too crowded to count — cosmology
- More small planets round smaller stars — exoplanets
- At a year, most candidates are noise — exoplanets
- A peak that neither survey can see alone — exoplanets
- Stars that weigh and do not shine — galaxies
- One acceleration, and every galaxy's missing mass — galaxies
- A third body kept at a safe distance — gravitation
- The lightest body leaves — gravitation
- A periodic orbit that the sky cannot keep — gravitation
- Every fragment comes back through the same point — orbits
- The variable that makes Lambert's problem easy — orbits
- A clock allowed to leave the Sun — the observed sky
- A clock made of neutron stars — the observed sky
- A graveyard height with a term for sunlight — spaceflight
- A peak that says where the electrons were made — spaceflight
- The photons on the sides of the lines — starlight
- A redshift that is wrong by three — starlight
- The last fuels burn for the neutrinos — stars
- A flow that piles up at the magic numbers — stars
26 September 2026
20 essays on gravitation, galaxies, stars, starlight, cosmology, exoplanets, orbits, the observed sky and spaceflight
- Inside a ring the pull points outward — gravitation
- Stars lost to a kick that adds no energy — gravitation
- A foreground drawn by the field it traces — galaxies
- A measurement of dark matter that needs a model of galaxies — galaxies
- A collision decided by a speed across the sky — galaxies
- A corona held by its field and opened by its gas — stars
- The same flux in three sizes — stars
- A colour that runs backwards at the end of cooling — stars
- A size read from the slope of a colour — starlight
- A wall built by a steep opacity — starlight
- A ruler shortened by something already gone — cosmology
- A lower limit made of three lengths and a missing echo — cosmology
- Molecules seen only through a change of temperature — exoplanets
- Dust that does not dim with distance — exoplanets
- A ceiling that forgets how much there was — orbits
- An orbit that turns over — orbits
- A past that can only be given as odds — the observed sky
- A core that wobbles at its own period — the observed sky
- Fifty objects that hold most of the future — spaceflight
- Braking on a moon before braking with the engine — spaceflight
25 September 2026
20 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, stars, spaceflight and starlight
- A crossing that may belong to the fitting form — cosmology
- The first three minutes use two lifetimes — cosmology
- A threshold that makes iron matter only to giants — exoplanets
- An angle hidden by the tilt of the star — exoplanets
- A spectrum that counts what no single gap can — galaxies
- A delay that tells which way the gas is moving — galaxies
- The part of a delay no orbit can imitate — gravitation
- An equilibrium reached without a single encounter — gravitation
- A denominator that emptied the inner belt — orbits
- An age read from angles that meet — orbits
- A full moon computed from the year number — the observed sky
- A sharp image kept by throwing the rest away — the observed sky
- A lifetime that is still a forecast — stars
- A distance that rests on one unmeasured number — stars
- The first weeks off a Hohmann transfer are nearly free — spaceflight
- A millimetre a second at launch, seventy-six kilometres at Mars — spaceflight
- The gap between the belts is a race between two clocks — spaceflight
- Odds for a planet that depend on a guess about its size — starlight
- An angle too small to measure, read from a colour — starlight
- The fainter polarisation belongs to the lobe further away — starlight
24 September 2026
20 essays on stars, starlight, exoplanets, galaxies, the observed sky, orbits, spaceflight, cosmology and gravitation
- A survival that depends on the energy — stars
- A ceiling on the light and not on the mass — stars
- A rate the wind has no choice about — starlight
- A temperature that is a speed — starlight
- An escape that stops following the starlight — exoplanets
- A null filled in by the star itself — exoplanets
- A horizon drawn by light at three kelvin — galaxies
- Two spins that cancel, and an orbit that leaves — galaxies
- A substorm timed by webers and volts — the observed sky
- A season without a night — the observed sky
- A kink that measures how deep the lava was — orbits
- A spike only first-time visitors can be in — orbits
- The cheapest circle to stop in — spaceflight
- A wall across the porkchop — spaceflight
- A shadow cast on the microwave background — cosmology
- An emptiness that expands faster — cosmology
- A field that would have moved the ruler — cosmology
- A disc that throws its spin upward — gravitation
- A core that makes what the cluster asks for — gravitation
- A barrier that leaks at a rate that can be computed — gravitation
23 September 2026
20 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- The shape a galaxy was given before it was lensed — cosmology
- A spin that remembers the field and not its sign — cosmology
- The gas that turns round beside the planet — exoplanets
- A planet circularised at twice the distance that would destroy it — exoplanets
- One eccentric planet, or two circular ones — exoplanets
- An exposure time chosen by the star — exoplanets
- Where the sky is the measurement — galaxies
- A radius that is a measurement of the threshold — galaxies
- The halo a galaxy drags inward — galaxies
- A constant measured through a Sun that is getting lighter — gravitation
- A spacing law that random orbits obey — orbits
- A hotter summer that is also a shorter one — orbits
- The size at which a body is easiest to break — orbits
- A square field imaged as a squashed one — the observed sky
- An atmosphere that bends light round the Earth — the observed sky
- The sky crowded forward by the observer's speed — the observed sky
- A time scale that is finished after it is used — the observed sky
- A belt emptied over one ocean — spaceflight
- A source that rotates its own light — starlight
- A core too heavy for the gas around it — stars
19 September 2026
20 essays on gravitation, spaceflight, starlight, galaxies, orbits, cosmology, exoplanets and the observed sky
- A ring whose size is almost only a mass — gravitation
- A spin that is measured as an angular momentum — gravitation
- A moon that two bodies could not have caught — gravitation
- A stability limit with a notch cut in it — gravitation
- The ratio that is not √2 — spaceflight
- The speed that is left over — spaceflight
- The relative orbit that breathes — spaceflight
- A camera that cannot see how far — spaceflight
- How much of the picture is the prior — starlight
- The position closure throws away — starlight
- A sight line stops at two thirds — starlight
- A limb brighter than the middle — starlight
- Two ways to stop that do not interact — galaxies
- A crossing time that is the filter's — galaxies
- A cycle that builds what the wave needs — orbits
- A ceiling the outer orbit imposes — orbits
- A blur undone with the field that made it — cosmology
- A ruler read in absorption — cosmology
- A reference built from other stars — exoplanets
- A rocking nobody started — the observed sky
16 September 2026
38 essays on cosmology, exoplanets, galaxies, the observed sky, spaceflight, starlight and orbits
- The darkness has a number in it — cosmology
- A background weighed by what it stops — cosmology
- Two skies where the paradox comes out right — cosmology
- The threshold that is not a threshold — exoplanets
- Every method prefers a circle, and not for the same reason — exoplanets
- How many planets a star has is not a measurement — exoplanets
- The count theory predicts, and the inference it costs — galaxies
- Two counts that are not the same shape — galaxies
- The same census, taken in two places — galaxies
- Five zones, and one angle — the observed sky
- The sunniest place is the summer pole — the observed sky
- The hottest month is not the sunniest — the observed sky
- One square root that raises the orbit and turns it — spaceflight
- The engine is chosen by the calendar — spaceflight
- A drive with no rocket equation — spaceflight
- The classical law gives every star one colour — starlight
- Two laws that are one curve read twice — starlight
- Three shifts larger than the error bar, and two that cancel — starlight
- A wall measures a ratio, and a ratio is a line — orbits
- Two damping times, one crossing, and the slope that separates them — orbits
- A velocity that has the colour of the sky — cosmology
- A null that moves with the temperature — cosmology
- Too few clusters, or a scale that reads light — cosmology
- A thermostat that only halves the error — exoplanets
- A year too short to feel its own eccentricity — exoplanets
- Steam before the zone existed — exoplanets
- The metals a galaxy keeps measure what it threw away — galaxies
- A gradient the old stars have walked away from — galaxies
- The iron clock has no single delay — galaxies
- A right angle short by a seventh of a degree — the observed sky
- A triangle of meetings that turns in eight centuries — the observed sky
- Brightest as a crescent, and not as a disc — the observed sky
- An unstable point that costs less to hold than a stable orbit — spaceflight
- The best aperture throws away a tenth — starlight
- The comparison stars are part of the measurement — starlight
- A spin barrier with a corner in it — orbits
- A split that decides whether the piece can leave — orbits
- A fuel gauge that is worst when it is needed — spaceflight
14 September 2026
20 essays on orbits, starlight, galaxies, gravitation, cosmology, exoplanets, the observed sky and spaceflight
- Only two force laws let an orbit come back — orbits
- The well moves, and the body keeps its share of it — orbits
- A spectrum with no continuum left in it — starlight
- The continuum is made by one atom in ten thousand — starlight
- Support that cannot be squeezed away — galaxies
- The support and the seed are the same motions — galaxies
- An ocean is detected and its depth is not — gravitation
- A quality factor quoted without a period is half a number — gravitation
- Half the ordinary matter was missing, and a millisecond found it — cosmology
- A mass measured by what it stopped from forming — cosmology
- A coincidence that is a factor of fourteen — cosmology
- There is not one line, there is a staircase — exoplanets
- A composition that dates a formation rather than placing it — exoplanets
- Two elements in a ratio, and a birthplace read off it — exoplanets
- The brightest instant of an occultation is its middle — the observed sky
- A population counted by shadows that never repeat — the observed sky
- Each event pays for the prediction of the next — the observed sky
- A coefficient that belongs to the surface, not the satellite — spaceflight
- A weather forecast made out of orbits — spaceflight
- A manoeuvre that has never been flown once — spaceflight
13 September 2026
20 essays on cosmology, exoplanets, the observed sky, spaceflight, galaxies and starlight
- The tilt knows the slope and not the height — cosmology
- A ratio that is an energy and a distance — cosmology
- The epoch nobody saw moves the tilt — cosmology
- A test that can only fail one way — cosmology
- A forecast that fails on a schedule — exoplanets
- A transit late by the width of an orbit — exoplanets
- One timing curve and five planets that could draw it — exoplanets
- A companion on the same orbit, seen in the planet's clock — exoplanets
- On Mars the orbit outweighs the tilt — the observed sky
- A Sun that stops and runs backwards — the observed sky
- The smallest term between a clock and the Sun — the observed sky
- An hour that stretched with the season — the observed sky
- A spin that left the axis it was given — spaceflight
- A wingnut that turns over on its own — spaceflight
- A boom held upright by a difference in gravity — spaceflight
- A tumble stopped by the field it tumbles through — spaceflight
- The speed a line width stands in for — galaxies
- A disc that turns slower than its mass requires — galaxies
- The pole-on stars a brightness limit prefers — starlight
- The circulation that should have stirred every fast rotator — starlight
11 September 2026
20 essays on spaceflight, the observed sky, cosmology, galaxies and exoplanets
- A swath is sized at the equator — spaceflight
- The circle a station can see — spaceflight
- A stationary satellite that draws a figure of eight — spaceflight
- A clock whose zero is moving — the observed sky
- Five satellites and not four — spaceflight
- A right ascension is a date — the observed sky
- The shadow that climbs the zenith — the observed sky
- A redshift that changes while it is watched — cosmology
- The line a star is swallowed at is not the horizon — galaxies
- The envelope that doubles a planet lasts longest — exoplanets
- An orbit feels the acceleration and never the rate — cosmology
- The age of the universe weighs the Local Group — cosmology
- The debris that returns fastest lights up last — galaxies
- The stars a black hole eats come from a narrow band — galaxies
- Ozone keeps the twilight zenith blue — the observed sky
- The air's height against the planet sets the twilight — the observed sky
- The stripping runs ahead of the starlight that drives it — exoplanets
- A smaller star puts the valley lower — exoplanets
- The young Sun's spin decides what the Earth kept — exoplanets
- The Sun's speed counted in quasars comes out twice too large — cosmology
9 September 2026
20 essays on cosmology, spaceflight, exoplanets and the observed sky
- The residue that failed to burn — cosmology
- A factor of three, and the flatness that prices every cure — cosmology
- An abundance with no direction to correct in — cosmology
- The universe that was lumpy at one second — cosmology
- The clock on which light travels in straight lines — cosmology
- Whether there is a horizon at all — cosmology
- Two horizons that differ only in who is inside — cosmology
- The split that is not an equal split — spaceflight
- Choosing a propellant is choosing a molecular weight — spaceflight
- Orbit costs 7.8 and a launch buys 9.4 — spaceflight
- An equation that does not break at the speed of light — spaceflight
- A rotation split between two burns — spaceflight
- Flying further away in order to turn — spaceflight
- A plane change paid at the worst speed there is — spaceflight
- An asymmetry that the Earth's own orbit puts in — exoplanets
- A centroid that moves when the brightness does not — exoplanets
- An event of a few hours and no host — exoplanets
- Two systems that draw the same curve — exoplanets
- Two fictitious suns in sequence — the observed sky
- The earliest sunset is not the shortest day — the observed sky
8 September 2026
20 essays on cosmology, exoplanets, galaxies, gravitation, orbits, the observed sky, spaceflight, starlight and stars
- A particle count taken from a dwarf galaxy — cosmology
- A length in centimetres, measured against an angle — cosmology
- The band moves and the orbit does not — exoplanets
- A mass that is only a mass once the eccentricity is known — exoplanets
- The factor that multiplies every quasar mass — galaxies
- A hole that says mass times time — galaxies
- A spin that is one length in disguise — gravitation
- The part of a kick that heats nothing — gravitation
- An average that precession cannot move — orbits
- A family whose size is a choice — orbits
- Nine dates for every surface in the solar system — orbits
- A tilt held still by being too fast to resonate — the observed sky
- An aurora that is a sixth root inside an arcsine — the observed sky
- The fragments nobody can see and cannot shield against — spaceflight
- The window that comes back and the cost that does not — spaceflight
- A diameter that depends on a model atmosphere — starlight
- A luminosity class is a density measurement — starlight
- An exponent that is a slope, not a law — stars
- A clock that stops while its interior freezes — stars
- Three clocks and a runaway — stars
5 September 2026
50 essays on orbits, gravitation, the observed sky, starlight, stars, spaceflight, exoplanets, galaxies and cosmology
- The series that is subtracted — orbits
- An eccentricity that cannot be zero — orbits
- Where a planet is and where it is seen — orbits
- The craters that were not primary — orbits
- An acceleration that was the spacecraft's own heat — orbits
- The drag that sorts a disc by size — orbits
- The part of a shape the spin cannot explain — gravitation
- A distance tangled with an angle — gravitation
- A drag computed with a logarithm nobody can pin down — gravitation
- An error that grows like a random walk — gravitation
- A heat flow that depends on a number nobody can compute — gravitation
- The atmosphere is a prism as well as a lens — the observed sky
- A second that depends on where the clock is — the observed sky
- A frame made of things that are not points — the observed sky
- An error budget added in quadrature — the observed sky
- A solar radius measured past a mountain range — the observed sky
- A velocity that is an average of lines that disagree — starlight
- A response measured pixel by pixel — starlight
- A continuum that was never observed — starlight
- A magnitude in a band the source never had — starlight
- The distance is not one over the parallax — starlight
- A sample brighter than the population it came from — starlight
- The tallest peak in nothing at all — starlight
- A temperature and a gravity that trade against each other — starlight
- An instrument more polarised than the sky — starlight
- Three causes with three shapes in one curve — stars
- A mass function corrected by an age — stars
- Two scaling relations calibrated on one star — stars
- A length nobody derived, fitted to one star — stars
- A convective boundary with no theory to fix it — stars
- A flux that is a thermometer to a tenth of a per cent — stars
- A satellite that drifts to one of two longitudes — spaceflight
- A density model wrong by a factor of two — spaceflight
- Four media between the antenna and the spacecraft — spaceflight
- The discontinuity a patched conic hides — spaceflight
- A duration that measures an eccentricity — exoplanets
- A planet radius is a stellar radius — exoplanets
- A star subtracted using the star — exoplanets
- A spectrum flattened by cloud, or by nothing — exoplanets
- A shadow crossing a rotating line — exoplanets
- A dispersion inflated by orbits nobody resolved — galaxies
- Two parameters that lensing measures as one — galaxies
- Three mass models that fit the same curve — galaxies
- A sheet of mass that changes nothing but the answer — galaxies
- One velocity and two distances — galaxies
- A dipole a hundred times the signal — cosmology
- A forest with no continuum left — cosmology
- An amplitude and a depth that arrive multiplied — cosmology
- A constant that is an angle divided by a length — cosmology
- A residual that is somebody else's velocity — cosmology
3 September 2026
20 essays on stars, starlight, gravitation, the observed sky, spaceflight, galaxies, cosmology, exoplanets and orbits
- A field that would have arrived ten thousand times too strong — stars
- The darkness a field pays for — stars
- A slope that needs no source — starlight
- The weakest field changes the answer — gravitation
- A boundary that hardly moves — the observed sky
- Three clocks and nothing to fall onto — spaceflight
- A direction measured by something with no strength in it — galaxies
- The energy at which a sky begins to point — galaxies
- The seed that cannot be remembered — cosmology
- A minimum that was mistaken for a principle — starlight
- Two instruments blind in opposite directions — starlight
- One step of memory kept at the poles — stars
- The flare that arrives from somewhere else — the observed sky
- The exponent no pulsar has — stars
- The period a star is pulled towards — gravitation
- A disc held open by what cannot be photographed — galaxies
- The shield that is also a funnel — exoplanets
- A resonance with the planet itself — orbits
- Two geometries and one bit to choose between them — galaxies
- A threshold with no free parameter in it — stars
1 September 2026
20 essays on stars, starlight, spaceflight, galaxies, gravitation, the observed sky, cosmology, orbits and exoplanets
- A wind that takes no mass and all the spin — stars
- The clock that starts by forgetting — stars
- A temperature that depends on where the observer stands — starlight
- The spin that has to be put somewhere — spaceflight
- A disc the size its halo was born with — galaxies
- The second number a black hole has — gravitation
- A tilt that is not a constant — the observed sky
- Spin acquired before there was anything to spin — cosmology
- A cut-off period that is an age — orbits
- Ninety-nine per cent of the mass and none of the spin — orbits
- A cloud that cannot become a star — galaxies
- A shear layer that should have spread — stars
- Every pair arrives circular — gravitation
- A neutron star born turning too slowly — stars
- An arm that is undone by the work it does — galaxies
- The last parsec, and the stars that are not there — galaxies
- A misalignment only cool stars forget — exoplanets
- A rotation locked to the orbit, but not one to one — gravitation
- A wobble that should have stopped — the observed sky
- A surface that slowed because the star grew — stars
30 August 2026
20 essays on stars, gravitation, orbits, galaxies, starlight, exoplanets, the observed sky, spaceflight and cosmology
- An equation of state is already a star — stars
- A clock with no fuel in it — stars
- A fluid that turns as one piece — stars
- How much a world gives — gravitation
- Whether the heavy material sank — gravitation
- A wall with no size in it — orbits
- An argument about the innermost kiloparsec — galaxies
- A floor under the centre that assumes nothing — stars
- Every note turns back at its own depth — stars
- A drift rate that says what the surface is made of — orbits
- The part of a star that never slowed down — stars
- A better measurement that made the model worse — starlight
- The depth is not the area — starlight
- A core weighed by something that never went in — gravitation
- One heat flow, and two viscosities — gravitation
- One density, and every planet that has it — exoplanets
- A radius no cold planet is allowed — exoplanets
- Four numbers that weigh a planet's core — the observed sky
- An ocean found in a Doppler residual — spaceflight
- A blur that measures a depth — cosmology
29 August 2026
20 essays on stars, galaxies, gravitation, orbits, starlight, exoplanets, cosmology and spaceflight
- The flow that narrows its own channel — stars
- A flare that puts a ceiling on a mass — galaxies
- A stream is not the orbit it came from — galaxies
- A pair that heats what is trying to cool — gravitation
- An answer obtained along a path that was not taken — gravitation
- Where the mass is and where the light is — orbits
- A speed read off an edge — starlight
- A drag that is strongest in the middle — gravitation
- The wake and the meal are one calculation — stars
- An edge is a balance, not a boundary — gravitation
- Capture is a direction, not a strength — exoplanets
- The precession that switches the cycle off — orbits
- An invariant that is only almost one — orbits
- A corner of the diagram that has to be earned — stars
- Red, gas-poor, and still spiral-shaped — galaxies
- It ends when the walls meet — cosmology
- Whether it merges is a ratio of two times — galaxies
- The planet pays, and it shows — spaceflight
- A torque that nearly cancels — exoplanets
- The companion survives, and it is moving — stars
28 August 2026
20 essays on orbits, gravitation, the observed sky, starlight, stars, spaceflight, exoplanets, galaxies and cosmology
- A surface dated by counting holes in it — orbits
- A comet that arrives a day early — orbits
- A ring weighed by the wave crossing it — gravitation
- One number where two masses were — gravitation
- A cluster that boils itself away — gravitation
- A star that blinked before it should have — the observed sky
- The faint star is measured against a brighter sky — starlight
- The dust is not lost light, it is moved light — starlight
- Two radii, from a light curve alone — stars
- A spectrum that is a stack of temperatures — stars
- A radius that decides what matter can be — stars
- Two explosions told apart by a missing line — stars
- An angle measured against a quasar — spaceflight
- The line beyond which ice counts as rock — exoplanets
- A planet ten times larger in one colour — exoplanets
- Two temperatures, and nothing in between — galaxies
- The cloud that cannot hold itself up — galaxies
- A birth rate measured from light nothing young emitted — galaxies
- A shadow that does not get fainter with distance — cosmology
- A map stretched by the thing it measures — cosmology
26 August 2026
15 essays on orbits, gravitation, the observed sky, starlight, stars, spaceflight, exoplanets, galaxies and cosmology
- A collision dated by a scatter plot — orbits
- A detector the size of the galaxy — gravitation
- The whole sky drifting towards one point — the observed sky
- The edge of a shadow is a wave — the observed sky
- A spectrum with no temperature in it — starlight
- A mean dominated by the gaps — starlight
- Two stars only a Fourier transform can tell apart — stars
- The only thing that leaves the centre — stars
- A position measured from a frequency — spaceflight
- A light curve with a fold in it — exoplanets
- A planet that was the star's own rotation — exoplanets
- A histogram that says the box was not closed — galaxies
- A distance measured with a stopwatch — galaxies
- A ruler measured along and across — cosmology
- A map that is not of positions — cosmology
25 August 2026
15 essays on orbits, gravitation, the observed sky, starlight, stars, spaceflight, exoplanets, galaxies and cosmology
- An orbit moved by heat — orbits
- The bound that holds only in the linear theory — orbits
- A distance with no ladder under it — gravitation
- A step that must not be adapted — gravitation
- A month that has to be tabulated — the observed sky
- A field strength read off a line that will not split — starlight
- A magnetic clock read off a butterfly — stars
- The mass a star does not keep — stars
- A map of the transfers that are free — spaceflight
- The gas a planet cannot keep — exoplanets
- The part of a rate that is a definition — exoplanets
- A size measured from a delay — galaxies
- The baryons that are not in the galaxies — galaxies
- The galaxies that are already out of reach — cosmology
- The number that would say whether it is a constant — cosmology
24 August 2026
15 essays on orbits, gravitation, the observed sky, starlight, stars, spaceflight, exoplanets and galaxies
- Aiming at a plane instead of at a planet — orbits
- Which direction moves which element — orbits
- The table that is a fit — orbits
- An error that is nearly all in one direction — orbits
- A feeding zone, and the spacing it forces — gravitation
- A moon heated by not being allowed to relax — gravitation
- A shape measured by the edge of a shadow — the observed sky
- A phase that survives what corrupts it — starlight
- A period found in the gaps — starlight
- Two orbits of one pair, and a distance falls out — stars
- A clock read against a model of everything in between — stars
- The same planet, three times — spaceflight
- A planet that is never confirmed, only validated — exoplanets
- The same curve, two galaxies — galaxies
- A one-per-cent distortion, and a million galaxies to see it — galaxies
22 August 2026
15 essays on orbits, gravitation, the observed sky, starlight, stars, spaceflight and cosmology
- No planet has an eccentricity of its own — orbits
- Three observations and no orbit at all — orbits
- One time of flight and five ways round — orbits
- Where the chaos comes from — gravitation
- The field a satellite is allowed to feel — gravitation
- How long a system takes to forget — gravitation
- The correction has to be faster than the air — the observed sky
- The direction a photon count throws away — starlight
- The same star through two telescopes — starlight
- The metre per second that is not the star — starlight
- A clock that runs down and says what it is — stars
- The valve that has to sit at the right depth — stars
- A burn that moves the wrong way — spaceflight
- A collision rate that needs no collision — spaceflight
- A trough that proves the forest survived — cosmology
21 August 2026
15 essays on orbits, gravitation, the observed sky, starlight, stars and spaceflight
- The singularity that is a change of variable — orbits
- The elements that stop existing — orbits
- An inclination that turns into an eccentricity — orbits
- The tunnel that takes the same time from anywhere — gravitation
- The system that gets hotter as it loses energy — gravitation
- The number that survives the encounter — gravitation
- The solar system measured from inside one orbit — the observed sky
- A year that is not a whole number of days — the observed sky
- The second thing a spectrum says — starlight
- Resolution without a mirror — starlight
- The error bar that comes from counting — starlight
- The explosion that never reaches the surface — stars
- The disc that has to throw angular momentum away — stars
- The tube that leads out of a neck — spaceflight
- The orbit that has to be paid for every year — spaceflight
20 August 2026
15 essays on orbits, gravitation, the observed sky, starlight, stars and spaceflight
- The third thing that is conserved — orbits
- The formula that exists, and is not used — orbits
- The surface a star stops at — gravitation
- An average that weighs what cannot be watched — gravitation
- A drag with nothing to drag against — gravitation
- Three definitions of night — the observed sky
- The wobble inside the wobble — the observed sky
- Five numbers from one wiggle — the observed sky
- The surface that is a depth — starlight
- A magnitude measured where nothing was measured — starlight
- An age read off a bend — stars
- Most stars are small, and most of the light is not — stars
- The candle that has to be standardised — stars
- A corridor a degree and a half wide — spaceflight
- The line under a satellite — spaceflight
19 August 2026
15 essays on orbits, gravitation, the observed sky, starlight, stars, spaceflight and exoplanets
- The one solve that does not ask which conic it is — orbits
- Two places and a clock decide the path — orbits
- Wrong about where, and right about how much — gravitation
- A prediction with an expiry date — gravitation
- The Earth's shape, read off a satellite's node — gravitation
- The other twenty arcseconds — the observed sky
- Six kinds of second — the observed sky
- A ten-metre mirror that resolves like a ten-centimetre one — the observed sky
- Why hydrogen's lines are strongest where hydrogen is not — starlight
- The light that is missing from the edge — starlight
- The resonance that had to exist — stars
- The mass a cold star cannot exceed — stars
- The transfer that costs more the gentler it is — spaceflight
- An orbit that speeds up as it is slowed down — spaceflight
- A velocity measured from a shape — exoplanets
17 August 2026
15 essays on orbits, gravitation, the observed sky, starlight, stars and spaceflight
- The orbit that has no period — orbits
- Five directions and no distance among them — orbits
- The average depends on what is being averaged — orbits
- A day five hours long — gravitation
- An orbit measured to be shrinking — gravitation
- The region a planet may keep a moon in — gravitation
- The loop a planet does not make — the observed sky
- The day that is four minutes short — the observed sky
- A magnitude has to say which light — starlight
- An angle of five hundredths of an arcsecond — starlight
- The same width for three different reasons — starlight
- The star that swells because its centre shrank — stars
- The interior read from a comb of frequencies — stars
- The cheapest place to turn — spaceflight
- The stage that has to be thrown away — spaceflight
15 August 2026
15 essays on orbits, gravitation, the observed sky, starlight, stars and spaceflight
- The wall that angular momentum builds — orbits
- Elements that do not stay constant — orbits
- The third law is wrong by the mass of the planet — orbits
- The curve that says where a body cannot go — gravitation
- Forty-three arcseconds, after everything else — gravitation
- Nothing in the sky is weighed in kilograms — gravitation
- The Sun sets before it sets — the observed sky
- The face that is not quite fixed — the observed sky
- Dust makes everything look further away — starlight
- How much of a line is not in its depth — starlight
- The only stars whose masses are known — stars
- A brightness that would blow the star apart — stars
- The part of a star that boils — stars
- The same burn is worth more when moving fast — spaceflight
- Two dates decide a mission — spaceflight
14 August 2026
15 essays on cosmology
- The shift that is not a Doppler shift — cosmology
- One number that is an age, a size and a density — cosmology
- The same constant, measured twice, five sigma apart — cosmology
- Four distances to the same galaxy — cosmology
- An expansion that was supposed to be slowing — cosmology
- The most perfect blackbody ever measured — cosmology
- A standing wave frozen at one instant — cosmology
- Four abundances and one free parameter — cosmology
- A budget whose familiar part is five per cent — cosmology
- The same ruler measured twice, ten billion years apart — cosmology
- Why the sky is dark — cosmology
- A horizon three times larger than the age allows — cosmology
- Two coincidences with one mechanism — cosmology
- Homogeneous above a hundred megaparsecs — cosmology
- The surface the background actually is — cosmology
13 August 2026
15 essays on galaxies
- A rotation curve that refuses to fall — galaxies
- The mass that is not the light — galaxies
- A galaxy measured from inside it — galaxies
- An arm that cannot be made of stars — galaxies
- Where a pattern is allowed to turn — galaxies
- A galaxy held up by disorder — galaxies
- A line width that is a distance — galaxies
- The brightness distance cannot touch — galaxies
- Weighed by the light that bends past it — galaxies
- A cluster weighed three ways — galaxies
- Two colours, and almost nothing between — galaxies
- A count with a knee in it — galaxies
- The mass at the centre that is not stars — galaxies
- A bridge and a tail drawn by one force — galaxies
- The gas runs out before the galaxy does — galaxies
11 August 2026
15 essays on exoplanets
- A planet measured by the light it removes — exoplanets
- Four contact points, and what they fix — exoplanets
- The star moves, and the mass is a lower bound — exoplanets
- Two methods, and one density — exoplanets
- A star magnified by a planet nobody will see again — exoplanets
- Nine orders of magnitude, half an arcsecond apart — exoplanets
- Every survey draws a different sky — exoplanets
- The planets that were not seen — exoplanets
- A gap in a histogram that says how planets are built — exoplanets
- Planets found by a transit running late — exoplanets
- A planet where one cannot form — exoplanets
- A chain that could not have been assembled in place — exoplanets
- A radius that depends on the colour it is measured in — exoplanets
- One number sets the zone — exoplanets
- The planet is seen when it disappears — exoplanets
10 August 2026
12 essays on orbits, gravitation, the observed sky, starlight, stars and spaceflight
- An orbit can look exactly like a circle and still not be one — orbits
- Three rotations that put an orbit in space, and they do not commute — orbits
- Two bodies replaced by one that does not exist — gravitation
- The distance at which a moon stops holding together — gravitation
- Where a star is depends on who is asking — the observed sky
- The eclipse that repeats a third of a world away — the observed sky
- Every distance is measured with the last one — starlight
- A brightness is a distance only if something is known — starlight
- A star is held up by its own weight — stars
- A star that tells its distance by how slowly it blinks — stars
- Going too far in order to arrive cheaply — spaceflight
- One trajectory, stitched from three two-body problems — spaceflight
3–7 August 2026
34 essays on orbits, gravitation, the observed sky, starlight, stars and spaceflight
- The orbit is an ellipse, and the Sun is not in the middle of it — orbits
- Equal areas in equal times, which is angular momentum in disguise — orbits
- The position that has no formula, and is computed anyway — orbits
- The law that links period to size, and weighs everything — orbits
- Every orbit one force allows, and the number that picks between them — orbits
- Six numbers that fix an orbit for all time, and the sixth is the awkward one — orbits
- One equation for the speed anywhere, and the eccentricity is not in it — orbits
- Neither body is still, and the wobble is how planets are found — gravitation
- A sphere pulls exactly like a point, and the proof is a pair of cones — gravitation
- The tide is a difference, which is why there are two of them — gravitation
- Five places that keep station, in a problem with no solution — gravitation
- Three bodies, and what "no solution" actually means — gravitation
- Resonance clears a gap in one place and locks a moon in another — gravitation
- The sphere that is not there, and why it is still the right model — the observed sky
- The Sun's path, and the tilt that makes the seasons — the observed sky
- Phases are not shadows, and eclipses are — the observed sky
- The pole star has a shelf life, and the sky has a slow hand — the observed sky
- The Sun is a bad clock, by up to sixteen minutes — the observed sky
- The triangle that reaches the stars, and stops — starlight
- A scale that runs backwards, multiplies, and works — starlight
- Colour is a thermometer, and it reads across the galaxy — starlight
- A shift in a line is a speedometer, and it works at any distance — starlight
- Composition, read from what is missing — starlight
- The diagram that sorted the stars, by plotting two things against each other — stars
- Mass decides everything, by a power of three and a half — stars
- Why the biggest stars die first, and take the galaxy with them — stars
- The furnace that runs cooler than a compost heap — stars
- The main sequence is a place stars sit, not a track they travel — stars
- A star held up by a rule about counting — stars
- The cheapest way between two orbits, and why it is so slow — spaceflight
- The speed that does not come back, and the √2 that separates it — spaceflight
- Stealing speed from a planet, which does not notice — spaceflight
- The exponential that decides what can be flown — spaceflight
- Catching up by slowing down, which cost Gemini 4 its fuel — spaceflight