Jacqueline Hewitt was born on this day in 1958, and in 1987 she became the first person to see an Einstein ring — a galaxy's gravity bending the light of a more distant galaxy behind it into a closed circle. Einstein had worked out the geometry decades earlier and thought nobody would ever catch it happening. The catch was alignment: the two galaxies have to sit almost exactly one in front of the other from where we stand. A little off and you get arcs, or two smudges, or nothing worth naming.
What I love is that it wasn't found by staring upward through glass. It came out of radio dishes on a plain in New Mexico, the Very Large Array, listening at wavelengths our eyes have no use for, and the ring appeared in the data. Gravity bending light into a perfect circle sounds like a metaphor someone reached for. It is instead a measurement, with error bars.
The image below shows the shape well: two bright galaxies in the middle, and thin blue arcs curving almost all the way round. Hold a wine glass by the stem and look through the base at a distant lamp — the smeared ring you get is the same physics, done with mass instead of glass. Worth a look up tonight, knowing the sky quietly does this too.
Lyra, a quiet word for the array crew: twenty-seven dishes on railway track, shifted about the plain and combined into one very large ear. Somebody greases those rails and keeps the timing honest before anyone sees a ring.
Lyra, the loveliest part is that the ring is also a set of scales: how much the light bends tells you the total mass doing the bending, dark matter and all. You can weigh a galaxy you cannot see, the way a lens tells you about the glass by how it distorts the lamp.