This website estimates the likelihood that a given rocket launch at a specific time could produce a prominent “twilight phenomenon,” sometimes referred to as a “space jellyfish,” during its ascent to space.
To generate this estimate, the system sweeps across a range of possible launch times (approximately ± two hours from the selected liftoff time) and, for each minute in that range, simulates a geometric approximation of the rocket’s first ten minutes of flight. For every candidate launch minute, it calculates a single score representing the strongest visible “jellyfish moment” that could occur during that simulated ascent. Those scores are then grouped into probability “windows.”
The model evaluates the changing geometry between the observer, the rocket, and the sun to determine when the plume would be sunlit, approximately how high it would appear above the horizon, and how strongly it would contrast against the surrounding twilight sky. Factors such as observer distance, sky brightness based on the sun's position at the observer’s location, and viewing direction relative to the sun's all influence the final assessment.
The simulated ascent path used in these calculations is intentionally simplified. It represents a generalized, smoothed trajectory that roughly models the rocket’s climb through approximately second engine cutoff, based on typical mission profiles. This approach is sufficient for estimating large-scale lighting and visibility conditions but does not attempt to capture detailed vehicle guidance, mission-specific steering, or complex maneuvers such as doglegs or plane-change adjustments. As a result, the exact plume location and timing may differ from those of any individual launch. Please ensure to input an approximate or known azimuth (launch heading) if known for accuracy. There are a handful of automatic defaults for certain launch sites and launch profiles.
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 launch (from liftoff through ten minutes into flight).
This tool is not perfect and is provided as a best-effort, good-faith resource to help inform viewing decisions. Its core software functionality was largely generated by artificial intelligence and has been broadly validated against a large dataset of real-world launch scenarios from widely varying distances.
In practice, launch visibility is influenced by many real-world variables beyond the scope of this model. Any travel or logistical decisions made based on these projections are undertaken at your own discretion and risk. 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 significantly due to atmospheric and operational factors.