
The streak of light moving across the sky over Quang Ngai Province, central Vietnam was captured by local residents. Photo: Taken from Facebook page of Huy Nguyen
On Tuesday morning, social media users in Vietnam shared images and videos showing a moving bright streak in the sky.
A Facebook group wrote that across the skies of Quang Nam Province, which was merged with Da Nang City on July 1, a strange phenomenon was observed—a long, moving light streak that caused concern among residents.
People in various central provinces and cities, including Da Nang and Quang Ngai, also captured footage of the unusual light streak.
The National Center for Hydro-Meteorological Forecasting confirmed that the phenomenon, as seen from Vietnam, was caused by China’s launch of the Tianzhou-9 cargo spacecraft using the Long March 7 rocket at 5:34 am Beijing time, or 4:34 am Hanoi time.
Weather expert Huy Nguyen also explained that the images recorded around 4:40 am over the eastern sky of central Vietnam showed the Long March 7 rocket carrying Tianzhou-9 into space.
The Long March 7 is a hypersonic rocket traveling faster than 8,575 km/h, which creates a 'sonic wall' behind it.
The cone-shaped white vapor trail behind the rocket is known as a condensation cloud or vapor cone.

The streak of light was photographed by locals at 4:39 am on July 15, 2025. Photo: National Center for Hydro-Meteorological Forecasting
According to Huy Nguyen, the visible white streak is the result of four key factors:
Shockwaves: As the rocket moves at hypersonic speed, it compresses the air in front of it, generating shockwaves. These waves reduce air pressure and temperature in specific areas behind the rocket.
Water vapor condensation: Under the low pressure and temperature conditions caused by the shockwaves, water vapor in the atmosphere condenses into tiny droplets, forming a white cloud. This cloud often appears cone-shaped.
Environmental conditions: The phenomenon is more visible in humid conditions, where more water vapor is available for condensation. In dry air, the vapor trail may not appear or be less noticeable.
Visual effects: The white streak is not smoke or burnt fuel but condensed water vapor. It typically appears and disappears quickly as the rocket moves through areas with different atmospheric conditions.
The National Center for Hydro-Meteorological Forecasting added that this phenomenon occurs when a rocket is launched at high altitudes, passing through the stratosphere or higher.
At that height, exhaust plumes from the rocket’s engines, including water vapor, propellants, and chemical particles, can be illuminated by sunlight from below the horizon.
These particles reflect the light, creating a bright white or colorful streak that stretches and spreads across the night sky.
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