36.71 light-years away
Arcturus
Why is this bright star moving the wrong way through the galaxy?
The brightest star in the northern sky is a visitor. It is not travelling with the disc of the galaxy the way the Sun and its neighbours are; it is cutting across.
A star from somewhere else
Arcturus is an orange giant, an ageing star that has exhausted the hydrogen in its core and swollen to some twenty-five times the Sun's diameter. At 36.7 light-years it is close enough to be one of the brightest things in our sky.
Its motion is what marks it out. Most stars near the Sun orbit the galactic centre in the same broad direction and plane, like traffic on a carriageway. Arcturus is moving at a steep angle to that flow, at high speed, along with dozens of similar stars — an old population that belongs to the galaxy's halo rather than its disc, currently passing through our neighbourhood.
Opening a World's Fair
For the 1933 Chicago World's Fair, light from Arcturus was collected by telescopes, converted to an electrical signal and used to switch on the exhibition's lights. The conceit was that the light had left the star during the previous Chicago fair of 1893, forty years earlier.
The distance was later revised and the arithmetic no longer works quite so neatly, which is a fitting detail: the stunt depended on a number that was still being measured. The principle, though, is exactly the one this tool is built on — the light you are looking at left a long time ago, and the delay is a distance.