Seriously I work outside and why is the feels like a real temp and the temp on record is taken in the shade?
In: 75
If you put a thermometer in the sun, it’s temperature reading will depend a lot on how much sunlight it absorbs. One painted black might read 20 or 40 degrees hotter than a clear glass one even though the weather is exactly the same.
We want our measurements to reflect the actual weather rather than how we build our thermometers, so we always measure with them in the shade.
The official temperature is the temperature of the *air*, so you measure it in the shade to avoid adding in solar heat.
Of course that means it’s not so useful for knowing how hot you’ll actually feel in direct sunlight. And it says nothing about humidity..
Because traditional temperature taking methods are overally simplified. A single dry bulb in the shade measures only air temperature and not humidity or solar radiation.
A ~~proposed new~~ better method of taking temperature for people working outside is called Wet Bulb Globe Temperature.
It is actually three thermometers: a wet bulb (which mimics sweat and accounts for humidity), a black bulb (which measures solar radiation), and a normal bulb in the shade (which measures air temperature.)
These three measurements can determine if it is safe for a person to work outside in the sun.
They want to measure the ambient air temperature. Exposing it to direct sunlight won’t accomplish that.
Like how your car’s interior gets a lot hotter than the outside air when in direct sunlight, so will a thermometer. The analogy is more appropriate for a glass mercury thermometer, but appropriate for a digital one as well.
Actually the military (American is all I’m familiar with to this degree) uses the wet bulb method which takes into account humidity and they measure both in the shade and in the sun inorder to take into account both direct sun temp shade temp and humidity which higher humidity makes it “hotter” because your sweat does less because there’s already moisture in the air. Your problem may be humidity not direct sunlight.
Your body is obviously warmed by the sun, so you might think: why not tell me how warm I’ll get? Trouble is: different materials absorb sunlight differently. If you put a black metal thermometer right in the sun, it will get much hotter than, say, a thermometer encased in white-painted wood. So you’d have to basically put a thermometer inside of a human body, in order to figure out how much it will be warmed by the sun on a particular day.
Not only that, but how much you are warmed by the sun also depends on your particular body, what clothes you are wearing, how much sun you are exposed to, and so on. So it’s impossible to get a single objective measurement that will be accurate for all or even most people.
Temperature in the shade, however, is very easy to measure objectively.
To compensate for factors like wind chill, humidity and sunlight, weather reports will often include a “feels-like” temperature which tries to correct for these things as much as possible, but again this won’t be accurate for everyone in every situation.
Because you’re using the thermometer to measure the temperature of the air. You’re making an assumption that the thermometer bulb/sensor is at the same temperature as the air.
If the sunlight shines on the thermometer, it will heat it up. It’s temperature will then depend on its aborbtivity, emissivity, mass, etc., etc.. The temperature indicated will just be the thermometer temperature.
It’s usual in building control systems to mount air temperature sensors on the north face of a building (northern hemisphere, always in the shade). The Contractors on one project put it on the west face. At some random time in the afternoon, the sun would hit it, the indicated temperature would go from 10 or 20 degC to 40 or 45 degC and the HVAC control would go loopy.
Sunlight heats up the thermometer (transfer of heat from the sun to the thermometer by light, by radiant energy). We want the temperature of the air, not the temperature of the air plus how much heating the sun is making on that object. Unless you actually do want the amount of heating caused by the sun, and then the cooling effects of interaction with the surrounding air is the problem.
The idea of a temperature measurement using a thermometer is that the mass of the thermometer gains, or loses, heat to the material it is immersed in. The thermometer is at thermal equilibrium (in balance with) the temperature of the surroundings. We want heat transfer by contact, not by radiant energy.
We do not actually want to know the temperature of the thermometer. We want to know the temperature of the air. That only works when the temperature of the thermometer is controlled only by the temperature of the air. Other heat (or cold) sources will give a false temperature reading, one where the thermometer says a temperature that is not the same as that of the air.
how is this question allowed? surely it breaks Rule 2?
The same reason you don’t put your AC thermostat in front of the air vent blowing cold air out.
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