Date
Chosen planet
–IHow long light takes
Light crosses 299,792 km every second, yet the Solar System is wide enough to make it wait. What you see of the Sun left it some eight minutes ago; Neptune as you see it tonight is four hours old.
Each bar is drawn on a scale that grows tenfold at every step, so a second, a minute, an hour and a day all fit on one line.
Distances from Earth for the date chosen above. Voyager 1 from NASA’s date for one light-day, 18 November 2026, and its speed of about 17 km/s; good to a few minutes.
IIComing up in the sky
Dates in UTC. Oppositions and the farthest points from the Sun are the best times to look; near a conjunction a planet hides in the Sun’s glare.