The Hong Kong Observatory delves into astronomy to deliver moon-watching tips for the upcoming Mid-Autumn Festival, and shares the science behind its observations in popular classes.
All eyes will be on the skies on the eve of September 8, as families gather to celebrate the Mid-Autumn Festival and observe the full moon.
The experts at the Hong Kong Observatory tell us the moon will rise at 5:51pm, and it will reach its highest point – known as the transit – at 11:55pm.
Hong Kong Observatory Experimental Officer Dickson Lau said the moon will be only about 1,000 kilometres further away from the earth than it was on August 11, the date of the so-called supermoon.
“If the weather condition is good, the moon will still be rather bright and round at night, and also look rather big,” Mr Lau said.
Knowledge shared
The observatory is much more than just a weather forecaster. Its mission is “to provide people-oriented quality services in meteorology and related fields, and to enhance the society’s capability in natural disaster prevention and response, through science, innovation and partnership”.
To that end, it also organises popular weather observation training courses for the general public, to help people forecast the weather themselves and respond adequately to changes in the weather.
Senior Scientific Assistant Judith Yeung says that one needs a clear understanding of the current weather condition before making a forecast. This requires weather observations that include temperature, humidity, air pressure, rainfall distribution and visibility readings.
Cloud clues
The training course covers cloud classification. Clouds are divided into three stages – high, middle and low-level – based on their height. According to their characteristic forms, they are classified into 10 types.
Ms Yeung said all 10 cloud types can be seen in Hong Kong, in different seasons. The most common clouds in summer are the puffy cotton-ball-like cumulus clouds, which are associated with hot weather and showers.
To teach course participants about visibility, they visit the rooftop of the observatory headquarters in Tsim Sha Tsui. From there, they have a panoramic view of some familiar landmarks that range from 100 metres to 50 kilometres in the distance, and can easily estimate visibility using them as a guide.
A check of the relative humidity, or amount of moisture in the air, can help determine whether it is likely to rain. Ms Yeung uses two thermometers, one wrapped in wet cotton, to gauge the temperature, using a reference chart that compares the two figures to provide the relative humidity.
Popular pastime
The weather observation courses are always oversubscribed. Those who miss the chance to attend can brush up on weather-watching techniques on their own, with the help of the observatory’s tools and videos posted on its website. Beyond weather, it also provides information on radiation, astronomy, earthquakes, natural wonders, and more, based on more than 130 years of science in the public service.
