What is a space jellyfish?

A massive space jellyfish could bloom across California skies tonight, created by the exhaust plume of a SpaceX Falcon 9 rocket. The phenomenon occurs when a rocket reaches the upper atmosphere after sunset, and its frozen exhaust particles catch the sun's light from below the horizon. The result is a glowing, jellyfish-like shape with long, luminous tendrils that can stretch for hundreds of miles.

Unlike typical rocket launches, which are visible only as a bright point of light, a space jellyfish is a rare and spectacular display. It requires a twilight launch, clear skies, and a specific viewing angle. Tonight's flight from Vandenberg Space Force Base is scheduled for 8:47 p.m. Pacific Time, just after sunset, making it ideal for the effect.

The launch and its path

The Falcon 9 will carry a new batch of Starlink satellites into low-Earth orbit. After liftoff, the rocket will head south, skirting the California coast. That trajectory means the space jellyfish will be visible from as far north as Eureka and as far south as San Diego, according to Dr. Elena Marsh, an astrophysicist at the Griffith Observatory in Los Angeles.

"The key is to have a clear view toward the southwest or west-southwest, depending on your location," Marsh said. "The jellyfish typically appears about three to five minutes after launch, when the rocket is at an altitude of 80 to 120 kilometers. That's when the exhaust spreads out in the thin air and catches the sunlight."

The display will last only a few minutes, so viewers should be in position before launch time. Observers in the Central Valley and along the coast will have the best chance, but mountains or tall buildings can block the view. The tool can help skywatchers find the exact spot.

A free tool for skywatchers

To help people know if they can see the phenomenon, a team at the University of California, Berkeley, has released a free web tool called Jellyfish Watch. The tool uses a user's location, the rocket's trajectory, and real-time weather data to generate a personalized visibility map with a countdown to launch.

"We built it after seeing how confused people were during the last space jellyfish event in 2024," said project lead Dr. Samuel Chen, a computational astronomer. "Our tool takes into account your coordinates, the predicted plume shape, and cloud cover. It tells you exactly when to look and in which direction."

Jellyfish Watch is accessible on any smartphone or desktop browser. Users simply click "Allow location" and the tool instantly displays a green checkmark if the sighting is likely, along with a sky map. It also includes a text alert system that sends a notification 10 minutes before launch.

Tonight's forecast and viewing tips

The National Weather Service predicts partly cloudy skies across most of Southern California, with some high cirrus clouds possible near the coast. Northern California should see clearer conditions, especially inland. Marsh advises checking the Jellyfish Watch forecast in the hour before launch, as marine layer clouds can move in quickly.

"If you see thin, wispy clouds, don't worry," Marsh said. "The glowing jellyfish is bright enough to shine through. What you need is a clear horizon. Go to a high spot like a hill or the roof of a parking garage. Let your eyes adapt to the dark for 10 minutes. Turn off your phone screen, or use night mode."

Space jellyfish sightings are not just beautiful. They also provide valuable data for atmospheric scientists. The plume's expansion reveals how winds blow at the edge of space, information that helps refine reentry models for satellites and spacecraft.

"Every time we get a good ground-based image, we learn something new about the upper atmosphere," Chen said. "So tonight, while you enjoy the light show, you can also be part of a citizen science effort. We encourage viewers to submit their photos through the Jellyfish Watch site."

Those who miss tonight's event may not have to wait long. SpaceX has another launch from Vandenberg scheduled for next month, and early forecasts suggest conditions could create another jellyfish. But tonight's timing makes it especially favorable. The next chance may not be as bright.