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Why does lightning always come before thunder?

“The God of Thunder was empowered by the Jade Emperor to punish bad people on the Earth. “ “Once, the God of Thunder mistakenly killed a kind-hearted woman.  The Jade Emperor, having looked into the matter, raised the woman from death and named her the Goddess of Lightning.  He also dictated that whenever the God of Thunder stroke the Earth, he must let the Goddess of Lightning release light first to distinguish the right from wrong and prevent injustice. “ The above is just a Chinese legend. In nature, a lightning flash and the associated thunder occur at almost the same time in a thunderstorm. A person on the ground sees the lightning flash before hearing the thunder because light at a speed of around 300,000,000 meters per second travels much faster than sound which moves at 340 meters per second.  If one is 1,000 meters away from the thunderstorm, he/she would see the flash almost instantly after lightning occurs as it takes just a few microseconds, while the thunder arrives only after about 3 seconds (1,000 meters divided by 340 meters per second). As a rule of thumb, by counting the seconds between the flash and the thunder and dividing the number by 3, you can estimate your distance from the thunderstorm in kilometers.  For example, if you hear the thunder 9 seconds after seeing the flash, the thunderstorm should be about 3 kilometers away from you.  If you see a flash and hear a thunder clap almost simultaneously, the storm must be very near you. Seek shelter immediately. (For more details, please click here to read the article written by Hong Kong Observatory) (Information provided by Hong Kong Observatory)

Scientific Officer

Miss Eunice Lee, a Scientific Officer of the Hong Kong Observatory, introduces the work of a Scientific Officer.A Scientific Officer is mainly deployed on performing weather forecasting duties, supervising and training staff and carrying out research in connection with the provision of services in areas including weather, climate, seismology, radioactivity, hydrometeorology, physical oceanography, aviation meteorology, marine meteorology and applied meteorology.A Scientific Officer may be required to attend training courses locally. He/She may also be sent on an overseas course in meteorology and/or other relevant subjects. He/She may be required to work outdoors, shifts, outside normal office hours, or in adverse weather condition. Organisation chartOfficial recruitment page

Experimental Officer

Mr Ken Wong, an Experimental Officer of the Hong Kong Observatory, talks about his career as an Experimental Officer.An Experimental Officer is mainly deployed on weather forecasting, data processing, radioactivity, hydrometeorological, physical oceanographic, seismological, and time services duties.An Experimental Officer may be required to attend a professional training course in meteorology during his/her probationary period. He/She may be required to work outdoors, shifts or outside normal office hours. Organisation chartOfficial recruitment page

Why do stars twinkle?

Since no astronaut while traveling in space has reported seeing stars twinkling, the effect must be atmospheric, i.e. due to air. However, it is not exactly correct to say that it is due to turbulence in the air.Mere turbulence in the air is just what we call wind. Wind does not make stars twinkle, because light travels at a great speed --- over 1 billion km/h.What distorts the light coming from a star is temperature variations in the air. As you probably know already, air temperature varies a great deal. It typically decreases by 6.5 degrees Celsius for every kilometre you go up, and this accords with the experience that it feels cooler up in the mountains. Also, on a hot day, you may notice the shimmering waves (thermals) that come off a heated road and make a distant car appear wavy.But exactly how do temperature variations cause twinkling?When light enters a transparent medium, such as air, it generally changes direction, i.e. it is scattered. By how much it changes direction, i.e. bent, however, depends on the temperature.Now any star, except the sun, is so far away that practically, it is sending only a single ray of light towards us. As that ray enters the atmosphere, it is scattered differently as it passes through air of different temperatures. When it is scattered away from us, the star seems to disappear for a moment. When it is scattered into our eyes, it seems to reappear, resulting in a twinkle.For more details, please click here to read the article written by Hong Kong Observatory. (Information provided by Hong Kong Observatory)

Why "a few degrees lower over the New Territories" often appears in the weather forecasts?

The phrase "a few degrees lower over the New Territories" often appears in the weather forecasts during autumn and winter, in order to remind the public of the temperature difference between different regions. This episode of "Cool Met Stuff" will briefly explain the cause of this phenomenon in the form of a playlet.    (Information provided by Hong Kong Observatory)