WHAT IS A SPACE JELLYFISH?
A “space jellyfish” occurs when a rocket and its exhaust plumes are illuminated by sunlight in the upper atmosphere or in space and an observer is in relative local darkness. This website estimates the likelihood that a given rocket launch could produce such an effect during its ascent.
Note: Some nighttime launches may be visible from great distances, even if they are not sunlit. Such cases are not modeled here.
HOW DOES THIS WORK?
The model evaluates the geometry between the observer, the rocket, and the sun to determine if and when the plume would be sunlit, approximately how high it would appear above the horizon, and how strongly it would contrast against the surrounding sky. Factors such as observer distance, sky brightness based on the sun's position, and viewing direction relative to the sun all influence the final assessment.
For each candidate launch time, the model finds the strongest post-liftoff moment and converts it into a likelihood/prominence label. It then outputs forecast labels in ten-minute increments for two hours on either side of T-0, with adaptive refinement near transitional periods so you can track forecast changes if T-0 shifts.
The simulated ascent path used in these calculations is a simple one. It represents a generalized, smoothed trajectory that roughly models the rocket's flight until second engine cutoff based on a handful of typical mission profiles. This approach is sufficient for estimating large-scale lighting and visibility conditions but does not attempt to capture detailed vehicle guidance or potential mission-specific maneuvers that are not widely known. As a result, the exact plume location and timing may differ slightly from reality or from those of any prior launch.
Importantly, the simulation focuses only on plume visibility during the immediate post-launch ascent phase. In certain circumstances, residual plumes from launches that occurred well before ideal lighting conditions may later become illuminated, depending on atmospheric factors such as upper-level winds. Those delayed illumination scenarios are not modeled here; this tool is intended solely for evaluating conditions immediately following liftoff.
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This tool is not perfect and is provided in good faith as a best-effort resource in an early-access beta period to help inform viewing decisions. Its core software functionality was largely created by artificial intelligence (its outputs are not AI-generated) and has been validated against a large dataset of real-world launch scenarios and subjective viewing experiences.
In practice, launch visibility is influenced by many real-world variables beyond the scope of this model (weather and atmospheric conditions, for example). Any travel or logistical decisions made based on these projections are undertaken at your own discretion and risk. If your prior real-world experiences differ from this model, trust your judgment. A favorable prediction does not guarantee a prominent, or even visible, jellyfish, and an unfavorable projection does not entirely rule one out, as launch appearances can vary for many reasons.
All information used to create this service and provide these predictions is based entirely on official, non-paywalled, public resources.
Outputs from this website may be referenced in news and media reporting, provided that clear attribution to jellyfish.johnkrausphotos.com is given in a manner reasonably visible to the intended audience.
To reduce the risk of misunderstanding, users should run a prediction for the specific location relevant to their audience before publication, and any visuals, including heatmaps, should be used as provided by this website rather than recreated, modified, or redrawn, with attribution retained in connection with any such use.