Seven stars: four in a bowl, three in a handle. The Big Dipper is not a constellation — it is the bright part of Ursa Major — but it is the best-known shape in the northern sky and six of its seven stars are brighter than magnitude 2.5. Find it once and you can navigate from it for the rest of your life.
The two stars at the outer end of the bowl — Merak at the bottom, Dubhe at the lip — are the pointers. They are 5.4° apart, which is roughly three fingers held at arm's length. Memorise that gap; it is the ruler for everything that follows.
Draw the line from Merak through Dubhe and keep going. 28.7° past Dubhe — five and a third pointer-gaps — the line arrives somewhere specific. Direction matters: run it the other way and you end up in Leo.
There it is: Polaris, alone in an otherwise empty patch of sky, at the end of the Little Dipper's handle. Nothing else of this brightness is anywhere near it, which is the real reason the hop works — you cannot mistake it for a neighbour, because it has none.
Polaris is not at the pole. It is 0.74° away — a degree and a half across, a Moon and a half wide — and it traces that little circle once a day. Magnitude 1.97 makes it only the 48th brightest star in the sky. It is famous for its address, not its brightness, and it is a Cepheid variable that has been slowly brightening for a century while it wobbles.
Twelve hours pass. Every other star swings through half a circle; Polaris moves by about a degree and a half and comes back. Watch the two numbers: the azimuth stays pinned near 0° and the altitude does not change. That constancy is what made it worth naming.
Now the part that makes it an instrument. Travel south and Polaris sinks; travel north and it climbs. Read the altitude as the location changes: 60°, then 40.7°, then 10° — the same as the latitude, every time. Polaris's altitude is your latitude. Fist on the horizon, stack fists to the star, count 10° a fist, and you have your position to within a degree. Navigators used exactly this for four centuries, with a correction table for that 0.74° wobble.
Do not get attached. Earth's axis precesses once every 25,800 years, so the pole drifts among the stars: Thuban in Draco held the job when the Egyptian pyramids were laid out, and in roughly 13,700 years the pole will pass within about 5° of Vega. Polaris is closest to the pole around the year 2100, at 0.45°. It is the best pole star for millennia either side, and it is temporary.