What can you see from where you are?

05 How this works

There are two quite different ways to see a rocket, and most tools only model one of them.

Close to the pad, you see the rocket itself. Nine Merlin engines are a 7.6 meganewton flame — self-luminous, nothing to do with sunlight. At night that carries several hundred kilometres; in daylight the vehicle and its contrail are unmistakable across the surrounding counties. This is why a midday launch is spectacular from the Space Coast and invisible from Georgia.

Far from the pad, you see sunlight on the plume. That is the twilight jellyfish, and it needs three things true at once. The interesting one is the third.

The rocket has to be above your horizon. An object at height h clears a flat horizon out to a surface distance of roughly √(2Rh). At 70 km — where a Falcon 9 stages — that is about 940 km. At 200 km, where the second stage shuts down, about 1,580 km.

You have to be in darkness. Below roughly 6° of solar depression the sky is still bright enough to wash the plume out.

And the plume has to be in sunlight. This is the whole trick. Earth’s shadow is a cone, so above any patch of ground there is an altitude beyond which sunlight still reaches. For a solar depression angle θ at the point directly below the rocket, the top of the shadow sits at:

The occulting body is not the solid Earth but the Earth plus its dense lower atmosphere — sunlight grazing below about 20 km is scattered and absorbed to nothing useful. Leaving that layer out puts the shadow roughly 20 km too low and makes every prediction three to eight minutes too optimistic.

The rocket climbs; the shadow it is flying over deepens. Whichever wins decides whether you see anything.

Where the trajectory comes from

Nobody publishes live rocket trajectories, so the flight azimuth is derived from the target inclination and the pad’s latitude, using the standard relation cos i = cos φ · sin A. From the Cape at 28.6°N, a 51.6° space-station inclination gives an azimuth of 45° — north-east up the seaboard, which is exactly where those launches go.

The altitude and downrange profile is digitised from published Falcon 9 and Falcon Heavy webcast telemetry: main engine cutoff near T+2:25 at about 70 km, stage separation seconds later, second-stage cutoff near T+8:45 at about 190 km. Other vehicles do not broadcast that data, so they use a generic profile scaled by lift class. The page tells you which of the two it used rather than implying a precision it does not have.

Upper-stage disposal — the one most people actually see

After the payload separates, the upper stage vents its remaining propellant and burns to come down. That cloud expands for hundreds of kilometres, which lifts it into sunlight long after your own sky has gone fully dark. It is the most commonly reported “strange spiral” sighting from Canadian latitudes, and it is visible far more often than a launch plume.

The stage never gets a published orbit before it reenters, so it cannot be tracked the way the space station is. It does not need to be: the parking orbit is fully determined by the pad, the launch time and the target inclination. The tool builds that orbit, propagates it forward and reports the passes over you inside the plausible disposal window. That is a watch window, not a timetable — operators do not publish burn times.