Before every launch, observers ask the same question: will I see the rocket jellyfish from here? The Launch Visibility Planner answers it for an upcoming flight and your location. It works out whether the exhaust will glow in sunlight against your dark sky, when that will happen, and where you should look.
How to use it
- Pick a launch. The list shows upcoming launches from North American pads, read from Launch Library 2. Choose Recommended to keep only the ones you would see in good or excellent conditions at their scheduled time, from your location or from one of 108 towns.
- Set your location. Press Use my location, search a city or town, or type a latitude and longitude. Until you do, the tool assumes you are in Montréal. Recommended locations lists the towns that would get a good view of this flight.
- Check the liftoff. The tool starts from the scheduled time, the NET (no earlier than). To try a different time, type a date and time in your own time zone or in UTC.
- Open Advanced settings if you need them. Screening height (20 km by default, 0 to 60 km) is how far above Earth’s shadow the rocket has to climb before sunlight reaches it. Lowest altitude (0° to 20°) lets you ignore the low sky that trees or buildings hide from you.
- Read the answer. The verdict tells you whether you will see the rocket, and When gives the time span. Where tells you which direction to face and the highest altitude the rocket reaches, counted in fists held at arm’s length, each about 10°.
- Play the flight. The horizon view shows the sky as you would face it, with the rocket and its jellyfish, while the map draws the ground track. Press Play, or drag the time in the flight.
- Try another liftoff. Launches often slip, so the “If the launch is delayed” panel shows a bar for each liftoff, 3 minutes apart. Copy share link passes the answer on, since the address carries every input.
How it works
For each launch, the tool reads the vehicle, the pad and the scheduled liftoff from Launch Library 2, then flies the rocket along a generic ascent profile: altitude and distance downrange against time, carried along a great circle from the pad on a preset launch azimuth. Eight profiles, Falcon 9 and Electron among them, are approximated from public webcast telemetry. The flight is judged second by second, for 8 to 10 minutes.
A second counts as visible when three things hold at once. Your sky is dark, with the Sun more than 6° below your horizon. The rocket is lit, meaning it is higher than Earth’s geometric shadow beneath it plus the screening height, because sunlight grazing Earth is absorbed low in the atmosphere. And it is above your lowest altitude. The Sun’s position follows NOAA’s equations (after Meeus), good to well under 0.1°, and leaves out refraction.
For Excellent conditions, the Sun must be 9° to 15° below your horizon at the rocket’s highest visible point, that point must be 10° or more up, and the rocket must stay in view for a minute or more. Other visible flights get Good conditions, or Possible, low on horizon when the peak is under 5°. If nothing is visible, you get Sky too bright, Rocket in Earth’s shadow or Below your horizon.
Keep in mind that the tool only works out lighting and geometry. It knows nothing of clouds or weather, uses a generic trajectory instead of the real flight path, and doesn’t predict how big or bright the exhaust cloud will be. Confirm the final time on the official webcast.
Formula
h_shadow = R · (1 / cos d − 1), and the rocket is lit when h > h_shadow + s
h is the rocket’s altitude, and h_shadow is the height of Earth’s geometric shadow above the point directly under the rocket, both in km. R is Earth’s radius, 6371 km. d is how far the Sun sits below the horizon at that point, in degrees; while the Sun is up there is no shadow at all. s is the screening height in km, 20 km by default.
Worked example
Say the Sun is 10° below the horizon under the rocket and s = 20 km. Then h_shadow = 6371 km · (1 / cos 10° − 1) = 6371 km · 0.01543 = 98 km, so the rocket is lit once it climbs above 98 km + 20 km = 118 km. The tool’s Falcon 9 low-orbit profile gets there about 228 s after liftoff, as long as the Sun stays 10° below.
Common questions
What is the rocket jellyfish and why does it happen?
It’s what you see when a rocket climbs out of Earth’s shadow into sunlight while you are still standing in darkness. Some people call it the twilight effect. The exhaust spreads out in the thin upper air and glows against your dark sky.
When can I see a rocket launch from my location?
Your chance comes with a flight in twilight, when your sky is already dark but the rocket can climb high enough to catch the Sun. Contrast is at its best with the Sun 9° to 15° below your horizon. In full daylight the sky is too bright, and deep in the night the rocket may only reach sunlight late in its climb, or not at all.
Does it know about clouds, and how accurate is it?
No, it only models lighting and geometry. The Sun’s position is good to well under 0.1°. The weaker points are the generic flight path, the 20 km screening height and the scheduled time itself. So a good verdict tells you when and where to look, but it can’t tell you what you will see.
What if the launch is delayed?
Look at the “If the launch is delayed” panel. It shows one bar per liftoff, 3 minutes apart, through your evening and morning twilights, and marks each one Visible, Low or Not visible. Slide to a time to see its verdict.
Does it need an account or store my location?
You don’t need an account, and nothing is stored apart from your theme and language. Your location does sit in the page’s address, though, so only share a copied link if you’re happy to share the place too. To find your time zone, Open-Meteo receives the name of a town you search, or a position rounded to about 100 m.
Related tools
In the store
Equipment this tool helps you choose, at David Astro: