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Scientific Assistant

A Student Scientific Assistant is mainly deployed on undertaking formal and on-the-job training for a period of two to three years in general scientific work, such as weather observing, coding and chart analysis, radioactivity monitoring, operation and calibration of scientific instruments, scientific computations, operation and utilisation of information technology systems and applications development.He/she may be required to work outdoors, shifts, outside normal office hours, or in adverse weather condition.(Note: A Student Scientific Assistant who has satisfactorily completed at least two years' training, passed a departmental examination and is considered to have fulfilled the requirements of the grade and service need may be promoted to the Scientific Assistant rank.) Organisation chartOfficial recruitment page

Why is February shorter than other months?

Why is the number of days in February smaller than that in other months?  How were the rules for leap year established? Do you know that leap years do not always occur every 4 years? These will be explained in the episode of "Cool Met Stuff".(The video is broadcasted in Cantonese) (For more details, please click here to read the article written by Hong Kong Observatory) (Information provided by Hong Kong Observatory)

Why does food taste bland on airplanes?

People having in-flight meals always find their food not particularly tasty. Is this a result of budget consideration of the airlines or some other causes?It may be interesting to note that some physical parameters of the environment would affect our sense of tastes. According to some foreign studies, under dry and low air pressure conditions, the sensitivity of our taste buds to sweet and salty food will be reduced by 30%. Charles Spence, a professor of Experimental Psychology at Oxford University, pointed out that food and drinks taste differently in the air as compared with that on the ground. There are several reasons for this. Among them, humidity, air pressure and environmental noise each plays a role.After the plane takes off and reaches the cruising altitude (usually at about 30,000 feet high), the flight attendants will start to serve meal to the passengers. It is noteworthy that as the plane climbs, the environmental conditions like humidity and pressure in the cabin also change, and these could affect our sense of taste and smell of food.At 30,000 feet, air in the cabin becomes very dry with the humidity drops significantly to the region of 20 percent or below. Due to lack of moisture, our sense of smell reduces and this affects our judgement on food taste. At the same time, lower air pressure will also affect the sensitivity of our taste buds. As a result, our perception of saltiness and sweetness of food also drops. All these make food taste blander inside the cabin of a flying aircraft. Of course, caterers of in-flight meals would endeavour to enrich the flavour of their food served aloft in response.In the atmosphere, pressure and temperature are changing all the time. It seems like ‘magic’ to generate various kinds of weather phenomena. Be it sunny, rainy, windy, and cold or hot, they all affect our outdoor activities. In fact, changes of these physical parameters in the environment also affect humans, at indoor venues or at some dozen thousand feet above the ground. (For more details, please click here to read the article written by Hong Kong Observatory) (Information provided by Hong Kong Observatory)

Why is candlelight yellow and gas-grill light blue?

Why is candlelight yellow and gas-grill light blue? It all depends on how much oxygen is around.  Lots of oxygen makes blue flames, while limited oxygen produces yellow flames.The amount of oxygen that is available for candlelight is still not sufficient to give complete combustion, i.e. for all the wax to become water vapour and carbon dioxide.  Under the heat, some of the wax (paraffin) breaks down into tiny particles of carbon, which is called soot.  These particles are heated up under the high temperature and glow with a bright yellow light.  This makes candlelight yellow.  On their way up the flame, most of the particles find enough oxygen to burn themselves out. Some of the carbon particles, i.e. soot, do remain, however.  You can catch them by putting a knife or spoon in the flame for a few seconds.  The blade will collect a black coating of carbon the same material you find on the inside of a chimney.  Soot is a source of pollution, and is commonly found in poorly maintained vehicles and from coal-burning homes and industries.All in all, there is too much fuel and too little oxygen going on in candlelight.  This makes the combustion far from an efficient process. In contrast, a gas-grill flame is more efficient.  It uses gaseous fuel, i.e. no vapourizing is required.  The burning is almost complete and the flame is much hotter than candlelight and can reach several hundred degrees Celsius.  The fuel molecules emit blue and green light when hot.  The human eye is more sensitive to blue light, hence we perceive a blue flame. (For more details, please click here to read the article written by Hong Kong Observatory) (Information provided by Hong Kong Observatory)

Why are spectacles or camera lens so difficult to clean?

Why are spectacles or camera lens so difficult to clean? It seems to get worse when an ordinary cloth is used, which tends to produce mult-coloured marks.When an ordinary cloth is used to rub grease off the glass, the grease becomes an additional coating with varying thickness. This produces multi-coloured reflections, because light is made up of different colours (i.e. different wavelengths). The 'rainbow' effect is similar to what we see when looking at a wet road with an oil film on it.What is the proper way to clean the glasses?Use the special cloth that comes with spectacles or camera lens. It is made of thin fibres that are good at picking up grease, rather than spreading it.A wet method involves washing with soap or a little liquid detergent. Then rinse, and leave it to dry or dry with a clean linen. You can also go to an optical shop for such a service. (For more details, please click here to read the article written by Hong Kong Observatory) (Information provided by Hong Kong Observatory)

Why does wet sand look darker than dry sand?

Water is colourless and transparent, but why is wet sand darker than dry sand? Is it because water absorbs more light than air? Not entirely correct. All else being equal, wet sand looks darker because not much light is coming out. For sand grains in water, the change in the direction of light is smaller than in air. On average, it takes a much longer path for light in wet sand to come out (left) than in dry sand (right). The longer the path, the greater the chance that light gets absorbed. Hence, wet sand looks darker than dry sand. (For more details, please click here to read the article written by Hong Kong Observatory) (Information provided by Hong Kong Observatory)

Myths about protection against UV radiation

Although most people are aware of the need to take protective actions against sunburn, there are some common misconceptions about UV radiation and the ways of protection: Myth 1: Darker sunglasses offer more protection from UV radiationThe most important thing to look for in sunglasses is how much UV radiation they filter out.  It should be noted that there is no relationship between the colour of sunglasses and their UV filtering action.  When one wears sunglasses the pupil widens as there is less light reaching the eye.  If the sunglasses have poor UV protection, the amount of UV radiation getting into the eyes may even be greater than not wearing sunglasses at all.  For adequate protection, one should wear sunglasses that are able to block at least 98% of the UV radiation. Myth 2: You can't get sunburn on a cloudy dayYou do get sunburned on a cloudy day, that is of course, if you are engaged in outdoor activities but not properly protected against ultraviolet radiation (UV).  It is true that on a cloudy day, you won't get as much exposed to UV from direct sunlight as when it is a clear sunny day.  However, sunlight, including UV, are scattered by gases in the atmosphere, as well as by clouds, dust, haze and even fog. Up to 80% of solar UV radiation can penetrate thin cloud cover.  There are also occasions when broken clouds enhance UV radiation by reflection from their sides.Therefore, in case of doubt, it is advisable to check the latest UV index through radio, television, the Observatory's website and Dial-a-Weather system (1878200). Myth 3: You can't get sunburn while in the waterWater offers only minimal protection from UV radiation.  At half a metre under water, the UV radiation level is still 40% as intense as at the surface.  Also, the part of body above water is additionally exposed to ultraviolet rays reflected from the water surface. Myth 4: Sunscreen lotion protects me so I can sunbathe much longerSunscreen lotion should not be used to increase sun exposure time but to increase protection during unavoidable exposure. The protection provided by sunscreen lotion depends critically on their correct application.  For more about sunscreen lotion and sunburn protection, please check out "Sunburn and SPF". Myth 5: If you take regular breaks during sunbathing you won't get sunburnUV radiation exposure is cumulative.  The total health damage you get will be the sum of the effect of individual exposure.  Therefore, to protect yourself the objective is to reduce exposure to UV radiation as far as practicable. This could decrease the chance of skin cancer. Myth 6: If you don't feel the hot rays of the sun you won't get sunburnSunburn is caused by UV radiation which cannot be felt.  The heating effect is caused by the sun's infrared radiation and not by UV radiation.  Therefore, even if you don't feel the warmth, you may also get sunburn. Human exposure to UV radiation may result in acute and chronic health effects on the skin, eye and immune system. So please be aware to take protective actions against sunburn. (For more details, please click here to read the article written by Hong Kong Observatory) (Information provided by Hong Kong Observatory)

The physics of gurgling

What causes the bubbling sound when drinking from a bottle?When drinking from an inverted bottle, a vacuum starts to appear at the top as water flows out of the bottle. Because of the air pressure outside, air forces its way through the neck of the bottle and bubbles up. This is followed by more water escaping, and more air bubbles moving up. So on and so forth. The glug-glug is caused by these two alternating processes.Does water flow faster at the beginning or near the end?Water flows faster at the beginning because this is when the pressure is highest.Does water flow faster when the bottle is in an inverted position (i.e. upside down) or when it is tilted?(The experiment can be carried out quite easily in a kitchen or bathroom. The result accords with our experience.)Water flows faster when the bottle is tilted, i.e. at an angle. This avoids the gurgling, i.e. air bubbles coming up through the liquid, which obstructs the passage of water.What is the fastest way to pour out water?The fastest way is to pour water at an angle and with a swirl. To create a swirl, move the bottle in small circles before pouring. This way, water moves to the side of the bottle and no gurgling occurs, allowing air to freely enter through the centre (For more details, please click here to read the article written by Hong Kong Observatory) (Information provided by Hong Kong Observatory)