The scale runs backwards, and it is Hipparchus's fault. He sorted the stars he could see into six classes — "first magnitude" for the brightest, "sixth" for the ones at the edge of vision — and the numbering stuck. Sirius is so far past first that it needs a negative: −1.44, the brightest star in the night sky.
In 1856 Pogson made the old eyeball classes arithmetic: five magnitudes = exactly ×100 in brightness. One magnitude is therefore the fifth root of 100 — 2.511886…, near enough 2.512 to work with and precisely not 2.512. The scale also needed a zero, and Capella at 0.08 is as close as the winter sky gets: calibrate your eye on it and everything else is a ratio away.
Polaris is magnitude 1.97 — the 48th brightest star in the sky, beaten by every star in the Big Dipper's bowl. Ask anyone which star is brightest and a good number say the North Star. It is famous for standing still. Fame and brightness are not the same axis.
Now calibrate. These five are in one view, so you can look from one to the next without your eye re-adapting: Sirius −1.44 → Rigel 0.18 → Betelgeuse 0.45 → Bellatrix 1.64 → Mintaka 2.25. End to end that is 3.69 magnitudes, which by Pogson's rule means Sirius delivers 30 times the light of Mintaka. Look at them and decide whether you believe it — most people underestimate badly, because the eye responds to light logarithmically and that is exactly what the scale was built to match.
Some of them move. Algol in Perseus is an eclipsing binary: every 2 days 20 hours 49 minutes a dim companion slides in front of the bright star and Algol drops from 2.1 to 3.4 and back inside ten hours. Watch it against Mirfak (1.79) and Almach (2.10): at maximum Algol matches Almach, at minimum it is obviously fainter than both. The whole thing is naked-eye, it takes one evening, and the Arabic name means "the ghoul".
Betelgeuse is the other kind of variable — irregular, a pulsating red supergiant that normally wanders between 0.0 and 1.0. In the winter of 2019–20 it did something else, sinking to 1.6, fainter than anyone alive had seen it, before recovering. It had ejected a cloud of dust that happened to drift across our line of sight. Rigel, meanwhile, holds 0.18 to within a tenth. A single number is a snapshot, not a property.
A Bortle 3 rural sky puts the faintest star you can see at about magnitude 6.5: roughly 9,000 stars over the whole celestial sphere, about 4,500 of them above your horizon at any moment.
The same sky under Bortle 7 — the suburban/urban transition — stops at about magnitude 5.0. That is 1,600 stars in the whole sky, some 800 overhead: you have lost 82% of them. Each Bortle class up costs roughly half a magnitude, and because the scale is logarithmic every half-magnitude is another 37% of the light gone. Orion survives it. Almost nothing faint does.
One skill to take outside. To estimate an unknown star, find two known ones that bracket it and judge where it falls between them — Orion alone gives you 0.45, 1.64, 1.69, 1.74, 2.07 and 2.25 within 20° of sky. That is the whole method professional variable-star observers used for a century, and with practice the human eye is good to about ±0.2 magnitudes. Your retina is a decent photometer. It just needs a reference.