In the early hours of June 6th, around 4 a.m., multiple residents in Xi’an, Shaanxi Province, captured footage of an unidentified flying object in the sky.

The video shows the object rising from the horizon, trailing a long plume that gradually spread out horizontally, forming a tadpole-shaped white phenomenon in the sky. A smaller part of the object later separated and continued to glide across the sky at a higher speed before fading into the night.

Authorities later confirmed that the “unidentified flying object” was actually a rocket launched earlier that morning, creating what is known as a “twilight phenomenon.”

The long tail was a rocket cloud. At 4:45 a.m. on June 6th, China successfully launched a group of low-orbit internet satellites (Group 04) aboard a Long March 6A rocket from the Taiyuan Satellite Launch Center. The satellites entered their intended orbit, and the mission was declared a complete success.

Scientifically known as a “twilight phenomenon” or “twilight effect,” rocket clouds are formed when the dust and water vapour in a rocket’s exhaust trail reach high altitudes and condense.

At such heights, the low atmospheric pressure allows the exhaust to expand dramatically, creating a wide, often colourful visual display as sunlight scatters through the particles. The colours can vary — including blue, orange, or even shifting hues — depending on the amount and type of high-altitude particles and the viewer’s angle.

6月6日凌晨4点多，陕西西安多位网友拍到不明飞行物，画面显示该飞行物从地平线上升空，拉出了一个很长的拖尾，慢慢地横向扩散，形成一个蝌蚪形状的白色天象，之后脱离出来一个小的部件，继续以更快的速度滑过天际，消散在夜空之中。

官方部门对此回应称，该不明飞行物其实是今晨发射升空的火箭在天空中形成的暮光效应，长长的拖尾实际上是火箭云。6月6日04时45分，我国在太原卫星发射中心使用长征六号改运载火箭，成功将卫星互联网低轨04组卫星发射升空，卫星顺利进入预定轨道，发射任务获得圆满成功。

火箭云，更专业的说法叫“暮光效应”或“暮光现象”，是由火箭等高速、超高音速航天器发射升空后，尾迹里的尘埃、水汽进入较高的大气凝结，在太阳光散射作用下形成的。暮光效应的传播距离非常远，而且因为达到了足够的高度，大气压力变小，尾气可以显著扩散变宽，就像突然爆开一样。它的颜色多样，有蓝色、橙色等很多种，也有变色，主要取决于高空中大量的微小粒子对太阳光的散射，以及观察者的不同角度。

陕西西安上空出现拖着长尾的不明飞行物