Our star, now

In visible light you see the surface, the photosphere, at about 5,500 °C, with sunspots as dark freckles: places where the magnetic field is so strong it holds back the heat from below, so they are 1,500 to 2,000 degrees cooler and look black against the rest. The magnetic map shows why: the spots sit on knots of field, white where it points towards us and black where it points away. In ultraviolet, higher layers light up, and they get hotter the further out you go, from the 50,000 degrees of the chromosphere to more than a million in the corona, a puzzle that is still not fully solved.

The Sun also blows a wind of charged particles, a few hundred kilometres a second, that takes days to reach us; the numbers above are NOAA's measurements of it, live, a million and a half kilometres in front of the Earth. Dark patches in the 19.3 nm picture, coronal holes, are where the fast wind leaves from. When a burst of it, or a cloud thrown off in an eruption, hits the Earth's magnetic field, the Kp index goes up and so does the aurora: the same numbers the orrery shows on its Sun card.

In the core, at 15 million degrees, hydrogen fuses into helium and the energy comes out as light. But the inside of the Sun is so dense that light gets less than a millimetre before it hits something and is thrown off in a random direction. It goes nowhere fast: a random walk, where getting twice as far takes four times as long. Estimates of how long the energy takes to struggle through the radiative zone run from tens of thousands of years up to about 170,000. Each zigzag on the screen stands for billions of real ones.

Two thirds of the way out the gas gets cool enough to boil instead: hot blobs rise, cool and sink, and carry the energy the rest of the way much faster. Their tops are the granules that cover the surface like rice grains, each about as wide as France and gone in ten minutes or so. Once at the surface the light is free, and covers the 150 million kilometres to us in 8 minutes and 19 seconds. The sunlight on your face is a few minutes old, and its energy older than farming.

Astronomers have watched sunspots since the first telescopes, around 1610, and this record of monthly counts goes back to 1749: the number rises and falls about every eleven years. The cycles are numbered from the one that began in 1755; we are in cycle 25, which began at the end of 2019. On the disc you can see two more rules at work. Early in a cycle the spots appear far from the equator, around 30 degrees north and south, and as the cycle goes on they show up closer and closer to it: drawn over time that makes a butterfly. And the Sun is not solid: the equator turns once in about 25 days, the regions near the poles in more than 30, so the spots near the equator drift past faster.

The beat is magnetic. The Sun's uneven turning winds up its field until it tangles and breaks through the surface as spots; around the top of each cycle the field flips, north becoming south. Not every cycle is equal: around 1800 there was a run of weak ones, the Dalton minimum, and from 1645 to 1715, before this record starts, hardly any spots were seen at all.