Five planets are bright enough to see with nothing but your eyes, and between them they are up on most clear nights of the year. The word is Greek — planētēs, wanderer — because these were the lights that refused to keep station with the rest. Every one of them is somewhere on the line drawn across this sky. The next five steps mark them one at a time, at tonight's positions, and each one carries a different way of telling a planet from a star.
Clue 1: it does not twinkle. Here is Jupiter at tonight's instant — the readout tells you whether it is up and where. Stars twinkle because they are true points, so a single pocket of turbulent air bends the whole beam at once. Jupiter shows a disc of 30 to 50 arcseconds, which is thousands of independent light paths averaging out, so it burns steadily and hard white at magnitude −2.9 at its best. Low down everything twinkles, atmosphere included; two thirds of the way up, a steady light is a planet.
Clue 2: it is on the line. The planets orbit in nearly the same plane as Earth, so they never stray more than about 7° from the ecliptic — and Saturn, marked here, is sitting on it like all the others. This is the strongest of the four tells, because it rules things out: a bright unfamiliar object well away from this line is a star you have not met, not a planet. Saturn is the dimmest of the naked-eye five at about magnitude +0.5 and a steady pale gold, so it reads as an unremarkable bright star until you notice it is not on the chart. It also gives the best payoff of any object in the sky: a telescope at 30× shows the rings, and nobody forgets the first time.
Clue 3: it is too bright for where it is. Venus reaches magnitude −4.9 — twenty times the light of the brightest star in the sky, enough to throw a shadow at a dark site and to be found in broad daylight if you know where to point. Nothing else up there but the Moon does that. If a constellation you know has acquired a new brightest star, you have found a planet, and if it is this bright you have found this one. Venus never strays far from the Sun, so it is a morning or an evening object and never overhead at midnight.
Clue 4: colour. Mars is genuinely orange-red — iron oxide dust on the surface, not an effect of our air — and it is the one planet whose colour a beginner reliably picks out unprompted. It is also by far the most variable thing on this list: −2.9 at a close opposition, when it outshines everything but Venus, and below +1.8 near conjunction. That is a factor of forty, and it is why Mars can headline one year and be unfindable the next.
Mercury is the one most amateur astronomers have never knowingly seen, and the reason is on screen: the measured arc is its elongation — its angular distance from the Sun tonight. That number can never exceed 28°, and is usually under 20°, so Mercury is permanently trapped in twilight, low in the west after sunset or low in the east before dawn. It reaches greatest elongation about six times a year. Pick one of those dates, find an unobstructed horizon, and start looking 30 minutes after sunset.
Now watch one wander. The camera is locked on Venus and three weeks run past — read the date. Venus stays centred; the stars slide, because Venus is moving against them at roughly a degree a day. That drift is the original discovery, the thing Babylonian scribes were recording four thousand years ago, and it is still the definitive test: note a suspect planet against two nearby stars tonight, look again in a week, and see whether the triangle has changed shape.
What to do with this outside. Because they all share one line, the planets keep running into each other: a conjunction, two planets within a degree or two, happens several times a year and is worth going out for. An outer planet is best at opposition — opposite the Sun, so it rises at sunset, transits at midnight and is at its closest and brightest. And since the Moon rides the same line, it passes each of them every month, which makes it the easiest finder chart there is: if a bright object is sitting beside the Moon, it is almost certainly a planet.