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TEMPERATURE MAPS
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Questions:
•What is temperature?
•What are the two most important factors in temperature?
•Why is it usually cooler at night?
•Why does temperature change during the seasons?
Air temperature is one of those things that everyone is familiar with, which turns
out to be more complicated than it might seem at first.
History of the Thermometer
In order to truly understand temperature, we must first understand how a
thermometer works. A thermometer is a device that measures the temperature of
things. The name is made up of two smaller words: "Thermo" means heat and
"meter" means to measure. You can use a thermometer to tell the temperature
outside or inside your house, inside your oven, even the temperature of your body if
you're sick.
Thermometers usually have a bulb at the base of the thermometer with a long glass
tube stretching out the top. Early thermometers used water, but because water
freezes there was no way to measure temperatures less than the freezing point of
water. So, alcohol, which freezes at temperature below the point where water
freezes, was used.
The red colored or silver line in the middle of the thermometer moves up and down
depending on the temperature. The thermometer measures temperatures in
Fahrenheit, Celsius and another scale called Kelvin. Fahrenheit is used mostly in the
United States, and most of the rest of the world uses Celsius. Kelvin is used by
scientists.
Fahrenheit is named after the German physicist Gabriel D. Fahrenheit who
developed his scale in 1724. Water freezes to ice at 32 degrees Fahrenheit (F for
short), and water boils at 212 degrees F. He arbitrarily decided that the difference
between the freezing point and boiling point of water should be 180 degrees.
The Celsius scale is named after Anders Celsius. The Celsius scale used to be called
the "centigrade" scale. Centigrade means "divided into 100 degrees." Anders Celsius
developed his scale in 1742. He started with the freezing point of water and said
that was 0 degrees Celsius (C for short). At the point where water boils, he marked
that at 100 degrees C. This scale is much more scientific because the measurement is
broken down into an even 100 degrees. This is similar to the scientific system of
measuring distance and weight called the metric system.
Kelvin is named after Lord Kelvin, whose full name is Sir William Thomson, Baron
Kelvin of Largs, Lord Kelvin of Scotland. His scale starts at 0 degrees Kelvin, which is
called absolute temperature.
Lord Kelvin took the idea of temperature one step further with his invention of the
Kelvin Scale in 1848. The Kelvin Scale measures the coldest temperature there can
be. He said there was no upper limit of how hot things can get, but he said there was
a limit as to how cold things can get. Kelvin developed the idea of Absolute Zero.
This is at minus 273.15 degrees Celsius (or -459.67 F)! At this temperature, absolute
zero is the lowest possible temperature, occurring when no heat energy remains in
a substance. Absolute zero is the point at which molecules stop moving.
As far as scientists know, nothing in the universe can get that cold!
How does a thermometer work?
When you look at a regular outside bulb thermometer, you'll see
a thin red or silver line that grows longer when it is hotter. The
line goes down in cold weather.
This liquid is sometimes colored alcohol but can also be a
metallic liquid called mercury. Both mercury and alcohol grow
bigger when heated and smaller when cooled. All matter is made
up of moving particles and when warmed, these particles move
faster. As the particles move they collide and spread out. Inside
the glass tube of a thermometer, the liquid has no place to go but
up when the temperature is hot and down when the
temperature is cold. Numbers are placed alongside the glass
tube that mark the temperature when the line is at that point.
Temperature is a measure of the average kinetic energy (or
energy of motion) of the various gas molecules that make up the air around a
thermometer.
The other type of common thermometer is a "spring"
thermometer. A coiled piece of metal that is sensitive to
heat is used. One end of the spring is attached to the
pointer. As the air heats, the metal expands and the
pointer moves higher. As the air cools, the metal contracts
and the pointer moves lower. Typically, these types of
thermometers are less accurate than bulb or digital
thermometers.
What factors affect temperature?
Temperature is affected by many things. Latitude is one of the main factors
affecting temperature. Latitude is the measurement of the distance of a location on
the Earth from the equator. The farther away from the equator that you are, the less
direct sunlight a location receives. Since Earth is round, not every place receives the
same amount of sunlight, or heat.
Another reason is due to the angle of solar incidence, this is the angle at which the
Sun's rays strike the Earth's surface. At the Equator, the Sun's rays strike the Earth
at a right angle, which makes the heat more intense and concentrated over a small
area. Less heat is lost to the atmosphere as the rays travel a shorter distance
through the atmosphere.
At the poles, the Sun's rays strike the Earth at an acute angle (less than 90 degrees),
this spreads the heat over a larger area. More heat is lost to the atmosphere as the
rays travel a longer distance through the atmosphere.
Another factor that affects temperature is altitude.
The Earth's surface absorbs most of the heat from the sun. Then, as the Earth's
surface warms up, the heat spreads into the lower layers of the atmosphere, and
transfers some of the heat to the upper layers of the atmosphere. As the air heats up,
it expands and becomes less dense, then becomes lighter, causing it to rise up above
the cooler air. As it does this, the air continues to expand. This is because there is
less pressure higher in the atmosphere, allowing the air molecules to spread out
more. So, the higher one travels into the troposphere, the lower the temperature
becomes.
Temperatures drop in the troposphere at a rate of 3.6 degrees for every 1,000 feet,
or 6.5 degrees Celsius for every 1,000 meters.)
The other factors that impact temperature include cloud cover, distance from the
sea, wind and ocean currents, and the length of day.
Why is it cooler at night?
An object will cool as long as it emits more energy than it receives. An object will
warm as long as it receives more energy than it emits. Therefore, the heating or
cooling of an object is cumulative. The amount of energy that has been taken away
or received over a period of time determines how much an object will warm or cool.
Take the earth's surface for example on a clear day. The sun has warmed the surface
during the day. Once the sun goes down, the earth's surface will begin to cool
(energy emitted is greater than energy received). This causes the earth's surface to
become progressively cooler during the night. The earth's surface is not coldest
right after sunset and not coldest in the middle of the night. It is coldest in the early
morning hours around sunrise. This is because cooling is cumulative. The longer an
object emits more energy than it receives, the more it will cool.
Why does temperature change during the seasons?
Why is it hot in the summer and cold in the winter? This is primarily due to the fact
that the earth is tilted on its axis. Many people believe that the temperature
changes because the Earth is closer to the sun in summer and farther from the sun
in winter, but this is not the case! In fact, the Earth is farthest from the sun in July
and is closest to the sun in January!
During the summer, the sun’s rays hit the earth at a steep angle. The light does not
spread out as much, thus increasing the amount of energy hitting any given spot.
Also, the long daylight hours allow the Earth plenty of time to reach warm
temperatures.
During the winter, the sun’s rays hit the Earth at a shallow angle. These rays are
more spread out, which minimizes the amount of energy that hits any given spot.
Also, the long nights and short days prevent the Earth from warming up. Thus, we
have winter!