Top Dog

Winter nights sparkle with some of the brightest stars in the sky: Rigel and Betelgeuse in Orion, Aldebaran in Taurus, and Procyon in Canis Minor, to name just a few. Yet it takes only a glance to pick out the brightest of them all: Sirius, the leading light of Canis Major, the big dog. That makes it the top dog. It’s in the southeast by mid-evening, and scoots low across the south during the night.
Sirius looks so bright in part because it is fairly bright — a couple of dozen times brighter than the Sun. But it also shows off because it’s just 8.6 light-years away. Only four other star systems are closer.
By astronomical standards, Sirius is just down the block. By human standards, though, the gap is pretty much incomprehensible — it’s far beyond any ordinary concept of “far away.”
To put it in everyday terms, the distance to Sirius is about 50 trillion miles — a five followed by 13 zeroes. To look at it another way, the farthest that any human has ever journeyed is the Moon. A one-wa