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Did you ever wonder…

  • Why it is warmer on some days than on other days?
  • Why some months of the year are colder than others?
  • Why it is almost always colder at the North Pole than at the equator?
  • How large bodies of water and mountains affect temperature?

Learning how and why the earth’s air temperature varies throughout the year and around the globe is the first step in understanding weather and climate.

Here you can explore some of the major factors that produce variations in air temperature.
Click the arrow on the right to get started.

Menu

The modules and activities listed in the menu on the right are intended to be completed in the order shown, but you can jump to any module at any time. Simply click on the menu tab at the top right of any page and then click on the module or activity you want. The module or activity you are currently using will be highlighted.

Daily Temperature Changes

You already know that temperature can vary from one day to the next. In this module you will get a better idea of how much the temperature changes from day to day at different places around the world.

"Cold front over Moscow on January 1, 2014" by Ivan Vtorov [CC-BY-SA-3.0], via Wikimedia Commons

Daily Temperature Variation over a Three-Week Period

The map above pinpoints Washington, DC. The graph on the following screen shows the average daily temperatures in Washington, DC over a three-week period. If you hover over the underlined words, average daily temperatures, you can learn more about that particular term and any other underlined term in these modules.

The graph shows the average daily temperatures in Washington, DC from April 2, 2000 to April 25, 2000. Notice that the temperature goes up and down from day to day in a jagged way.

If you hover the cursor over the line on the graph, the date and temperature for each point of the line appear. You can see how much change there is in the average temperature from day to day.

Notice that in this example, on April 9, 2000, the average temperature for that day was 43 degrees Fahrenheit. But the day before, on April 8, the average temperature was 65 degrees Fahrenheit.

That's a big change in one day's time. The second part of this module will help you understand how the temperature at a particular location can change so much from one day to the next.

The Movement of Air

You have now seen that temperature at a particular place can vary considerably from one day to the next. This variation is caused by the movement of large masses of warm and cool air.

As the wind blows, warmer or cooler air is constantly moving into and out of an area, and this movement of air changes the temperature at that place.

To see how clouds and, therefore, air move across the United States, click on the following web links. The cloud movement has been speeded up, but you can see from these videos that the air above us is always moving. Sometimes warmer air is moving in from another location and sometimes colder air is moving in. This never ending process goes on continuously around the world.

Module Complete

Quiz Yourself:

  • Does the average temperature at a place change from day to day in a regular pattern or are there both up and down changes from day to day?
  • Describe the effect of the movement of large air masses on daily temperature.

Expand Your Knowledge:

Find out how air masses form.

Annual Temperature Patterns

In the last module you saw that temperature can change considerably from one day to the next. In this module you will explore how temperature can change from day to day over the course of an entire year--from winter to spring to summer to fall--and from year to year.

By Eirik Solheim [CC-BY-SA-3.0], via eirikso.com

Temperature Over a Three-Year Period

The graph above shows how average daily temperature in Washington, DC changed between January 1, 2000 and January 1, 2003.

What do you notice? Does the graph have a pattern? How often does the pattern repeat?

You should see that the temperature rises and falls consistently throughout each year. But is the pattern always exactly the same? Hover over the line on the graph and find the high and low temperatures each year. If you would like to see a section of the graph in more detail, just use your cursor to click and drag a box around it. You can always zoom back out by clicking on Reset View at the top right side of the graph.

In some years in Washington, DC, the coldest day may be in December. In others, it may be in January. The warmest day is usually in July or August. Note that the high and low temperatures vary from year to year as well. The warmest day in 2002 was warmer than the warmest day in either 2000 or 2001. While the pattern is similar from year to year, it is clearly not identical.

Another way to think about annual temperature variation is by looking at the line on the graph. Does the line increase smoothly from the lowest temperature to the highest temperature of each year? Is the shape of the line the same from year to year?

The line is jagged because temperature varies from day to day. Because of daily temperature variation, not every July 1st is going to have the same temperature and not every July 2nd is going to have the same temperature.

You will now have a chance to observe annual temperature patterns at locations and dates of your choosing. See if other locations in the United States have annual temperature patterns of warmer summers and cooler winters. When you look at the annual temperature patterns over a period of several years, do the day-to-day changes look exactly the same each year?

Try It: Annual Temperature Patterns

1. Choose a place on the map. Choose starting and ending dates that cover more than just a single year. Click the "Start" calendar, and then click a specific date to choose the starting date. Click the "End" calendar, and then click a specific date to choose the ending date.

2. Observe the temperature pattern at that place.

3. Repeat this activity for as many different locations as you like before moving to the next activity. You can push the red button to reset your dates and markers.

Module Complete

Quiz Yourself:

  • For the places that you looked at in the United States, can you observe a pattern in how the average daily temperature changes throughout the year? If so, describe the pattern.
  • For the places that you looked at in the United States, is the pattern of average daily temperature change exactly the same from year to year?

Expand Your Knowledge:

What causes annual temperature patterns?

Latitude and Temperature

In the last module, you saw how temperature changes in a regular pattern over the course of a year. In this module you will see that the latitude of a place, that is, how far north or south a place is from the tropical zone, is related to the pattern of average daily temperature at that place.

Northern Hemisphere

In this activity you will look at the relationship between latitude and average daily temperature in the northern hemisphere.

In the map above, Winnipeg, Manitoba in Canada and San Antonio, TX in the United States are pinpointed. These two locations are about 1,000 miles apart.

The graph shows the average daily temperatures in Winnipeg and San Antonio from January 1, 2004 to December 31, 2004.

Look at the pattern of temperatures at the two places.

Notice that it is warmer every day of the year at the place that is farther south (the upper line).

As a general rule, in the northern hemisphere, places that are farther south (closer to the tropical zone) tend to be warmer than places that are farther north (farther away from the tropical zone). Within the tropical zone, the latitude where the temperature is the warmest changes gradually throughout the year. Sometimes it is at the northernmost boundary of the tropical zone, sometimes it is at the equator, and sometimes it is at the southernmost boundary of the tropical zone.

You should also notice that the difference between the highest temperature of the year and the lowest temperature of the year--what we call the range of temperatures--is less the closer you are to the tropical zone.

Notice that the range of temperatures at Winnipeg, the location that is farther from the tropical zone (the lower line), is greater than the range of temperatures at San Antonio, the location that is closer to the tropical zone (the upper line). This makes the line that is closer to the tropical zone (the upper line) a little flatter than the line that is farther from the tropical zone (the lower line).

Southern Hemisphere

Now let's look at two locations in the Southern Hemisphere. On the map above, Santa Cruz de la Sierra, a city in Bolivia, and Cordoba, a city in Argentina, are pinpointed. These two locations are about 1,000 miles apart.

The graph shows the average daily temperatures in Santa Cruz de la Sierra and Cordoba from January 1, 2004 to December 31, 2004.

Notice that at these two places, both of which are in the southern hemisphere, it is colder almost every day of the year in the place that is farther south.

As a general rule, in the southern hemisphere, places that are farther north (closer to the tropical zone) tend to be warmer than places that are farther south (farther from the tropical zone).

Just remember that in both the northern and southern hemispheres, places closer to the tropical zone tend to be warmer than places that are farther away from the tropical zone.

You will now have a chance to compare annual temperature patterns at two locations that you choose. See if the relationship between latitude and temperature you observed in these examples exists in other locations.

Try It: Latitude and Temperature

1. Choose two places on the map that are directly north and south of each other (on the same longitude) and at least 1000 miles apart.

2. Now use the calendar to choose a date range. Choose two dates that are one year apart. For example, you could choose January 1, 2000 and December 31, 2000. Click on the "Start" calendar to choose a starting date and the "End" calendar to choose an ending date.

3. Choose two other places and see if the pattern holds in those places too. Just make sure they are far enough apart so that differences in temperature are large enough to show up on the graph. Try as many additional pairs of places as you would like.

Module Complete

Quiz Yourself:

  • In the Northern Hemisphere, what is the relationship between how far north a place is and temperature?
  • In the Southern Hemisphere, what is the relationship between how far south a place is and temperature?
  • What is the relationship between how far a place is from the tropical zone (latitude) and its average daily temperature?

Expand Your Knowledge:

Find out why distance from the tropical zone is related to the temperature of a place.

Elevation and Temperature

In the previous module, you saw that the temperature and latitude of a place are related. The higher the latitude (farther from the tropical zone), the colder the place is, and the lower the latitude (closer to the equator), the warmer the place is.

In this module, you are going to use the maps to find out if how far a place is above sea level is related to the temperature at that place.

Temperature at Two Elevations

Are temperature and how high a place is above sea level related? This activity looks at temperatures at two locations with different elevations to find out.

The map is centered on the Himalayas, a mountain range between India and China, which is home to the planet's highest peaks, including Mt. Everest. Kathmandu, the capital of Nepal, is pinpointed.

The yellow dots represent the 20 closest reporting stations to Kathmandu. Zoom in three clicks (on the + sign) to get a closer look at where those reporting stations are located.

Because of the mountain range, there is a wide variation in the elevation of these reporting stations. Hover over the reporting stations to see if you can find the highest and lowest elevations.

Find the stations labeled Tingri (northeast of Kathmandu in Tibet) and Gorakhpur (southwest of Kathmandu in India). How do their elevations compare?

Tingri is about 14,000 feet above sea level, whereas Gorakhpur is only about 250 feet above sea level.

Click on the reporting stations in Tingri and Gorakhpur. Then move to the next page.

The graph shows the average daily temperatures in Tingri (14,108 feet above sea level) and Gorakhpur (253 feet above sea level) from January 1, 2004 to December 31, 2004.

What do you notice about the graph of the temperatures at the two locations?

You should see that even though both places have a similar pattern of rising and falling temperatures throughout the year, the place at the higher elevation (Tingri) has a consistently lower temperature throughout the year.

You will now have a chance to observe the relationship between elevation and temperature at locations of your choosing. See if other mountain locations experience lower temperatures compared to nearby locations at lower elevations.

Try It: Elevation and Temperature

1. Now you can explore other places where there are very high mountains, such as the Rocky Mountains in North America, the Alps in Europe, or the Andes in South America. Zoom in on the location you would like to explore on the map. As you move the cursor around the map, notice that the elevation appears in the information bar just below the map.

2. Click on a specific location on the map. Remember that the 20 closest reporting stations appear as yellow dots around the selected location. Zoom in to get a better look at where those reporting stations are. Hover over each of the yellow dots until you find two reporting stations that have a significant difference in elevation (at least 1,000 feet). Click on both stations to highlight them. You can click on more than two stations, but then the graph may be harder to read.

3. Now use the calendar to choose a starting and ending date. Pick dates at least one year apart. If you get a graph for only one of the locations, it may be because no data was reported at that station. Just click on another dot until you get a temperature graph for two different locations.

4. Remember to compare locations that are fairly close to each other. If the two locations are too far apart, something other than elevation may be responsible for the difference in temperature.

Also note that you may have difficulty finding reporting stations at extremely high elevations because those areas are often very remote and not easily accessible by humans.

5. You can repeat this activity as many times as you like until you are satisfied that you have a good understanding of how much the elevation of a place affects its temperature.

Module Complete

Quiz Yourself:

  • What is the relationship between the average daily temperature and elevation?

Expand Your Knowledge:

Find out why temperature is related to elevation.

Large Bodies of Water and Temperature

In the previous modules, you saw that the temperature at a place is related to how far the place is from the tropical zone (its latitude) and that temperature at a place is related to how far the place is above sea level (its elevation). The greater the latitude (farther from the tropical zone), the colder the place is, and the higher the elevation of a place, the colder the place is. This assumes, of course, that all other factors are kept constant. Obviously a place in the Rocky Mountains in the summer could be warmer than a place in New York City in the winter.

In this module, you are going to find out whether the temperature at a place is related to how close the place is to a large body of water.

By Ragnilius. (Image: Tromso, NO) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

Temperature Near Large Bodies of Water

Are temperature and how close a place is to a body of water related? This activity looks at temperatures at two locations that are different distances from a large body of water to find out.

In this activity you will explore the temperature patterns in Tromso, which is on the coast of the Norwegian Sea and is one of the northernmost cities on earth (pictured in the module introduction). You will also explore temperature patterns in Kautokeino, a small village about 125 miles southeast of Tromso.

Zoom two or three clicks to get a closer look.The yellow dots represent the 20 reporting stations closest to the marker.

Find the reporting stations labeled Tromso and Kautokeino and click on them. Tromso is northwest of the marker and Kautokeino is southeast.

The graph shows the average daily temperatures in Tromso and in Kautokeino from January 1, 2004 to Dec. 31, 2004.

The graph shows that in the winter and early spring in Kautokeino, which is farther from the water, the average temperature is quite a bit colder than in Tromso, which is closer to the water. In the summer, Tromso is a little cooler than Kautokeino.

You should also notice that the line on the graph for Tromso, the place that is closer to the water, is flatter than the line for Kautokeino, the place that is farther from the water.

In other words, there is a bigger range between high and low temperatures during the year in the place that is farther from the water. The high temperature is higher, and the low temperature is lower the farther a place is from a large body of water.

The reason for these patterns is that the temperature of the water has an effect on the air around it. Because water heats up and cools down more slowly than land, the range in air temperature near large bodies of water throughout the year is smaller.

You will now have a chance to observe the effect of closeness to a large body of water on temperature at locations of your choosing. See if other locations near a large body of water experience cooler summers and warmer winters compared to nearby locations farther inland.

Try It: Large Bodies of Water and Temperature

1. Use the map above to zoom in on a location near a large body of water that you would like to explore. Click on a specific location on the map.

2. The 20 closest reporting stations appear as yellow dots around the location you chose. Zoom in to get a closer look at where the yellow dots are located. Choose one reporting station that is as close to the large body of water as possible. Choose a second reporting station that is farther inland. Click on both reporting stations to highlight them. You can click on more than two stations, but then the graph may be harder to read.

3. Now click on the "Start" calendar to choose a starting date and the "End" calendar to choose an ending date. Pick dates at least one year apart. Then click the right arrow to continue.

4. When you choose locations, make sure that they are at approximately the same elevation. If one of them is at a much higher elevation than the other one, it will be difficult to tell if the different patterns you see are due to elevation or how close the two places are to a large body of water. Coastal areas often have mountains nearby, so when comparing two locations make sure one of them is not in the mountains and the other at sea level.

Also note that you may have difficulty finding reporting stations that are very close to large bodies of water because there aren't many reporting stations right on the shoreline.

You will also see that the closeness to a large body of water does not always have the same effect on temperature from place to place. At some places the effect is barely noticeable, and at other places it is very strong. This is because other factors, such as wind direction, can also have an effect on how much of the warmer or cooler air that is over the water gets inland.

5. You can repeat this activity as many times as you like until you are satisfied that you have a good understanding of how being close to a large body of water affects the temperature at that place.

Module Complete

Quiz Yourself:

  • In the winter, what effect does a large body of water have on average air temperature over nearby land?
  • In the summer, what effect does a large body of water have on average air temperature over nearby land?
  • What effect does a large body of water have on the range between high and low temperatures throughout the year over nearby land?

Expand Your Knowledge:

Find out how the properties of water cause large bodies of water to have a moderating effect on average air temperature over nearby land.

Height of the Sun in the Sky

In the last three modules you saw that there is a relationship between the temperature at a place and its latitude, elevation, and closeness to a large body of water. In this module you will begin to explore the relationship between the height of the sun in the sky and temperature at a place.

Height of the Sun in the Sky Over a One-Year Period

The map above pinpoints New York City.

The graph shows the maximum height of the sun in the sky in New York City for each day of the year.

In this graph you can see that the shape of the line is similar to the shape you saw in the graphs in Module B. The height of the sun increases and then decreases over the course of the year just as temperature increases and then decreases throughout the year. What you don't see here is the jagged pattern of day-to-day changes that you saw for temperature.

How high the sun gets in the sky changes smoothly from day to day because there is nothing besides the continuous movement of the earth and sun to affect it.

You will now have a chance to observe annual patterns of the height of the sun in the sky for locations and dates of your choosing. See if other locations have annual patterns that are similar to those in New York City.

Try It: Height of the Sun in the Sky

1. Choose a place anywhere in the world.

2. Choose a range of dates spanning at least a year. Click on the "Start" calendar to choose a starting date and the "End" calendar to choose an ending date.

3. Repeat this activity choosing a location within the tropical zone. Notice that you will see a different pattern. Why do you see that different pattern? You may find the "Expand Your Knowledge" activity on the next screen will help you answer this question.

4. Repeat this activity for as many locations as you like before moving on to the next activity. You can push the red button to reset your dates and markers.

Module Complete

Quiz Yourself:

  • For any place in the United States, how does the maximum height of the sun in the sky during winter compare to the maximum height of the sun in the sky during summer?
  • Consider the graph of the average daily temperature throughout the year from module C and the graph of height of the sun in the sky throughout the year from this module. Why is the graph from part C jagged and this graph smooth?

Expand Your Knowledge:

Use the Seasons Simulator, to see how the position of the earth with respect to the sun at different times of the year causes the maximum height of the sun in the sky to change in a repeating pattern.

Height of the Sun in the Sky and Temperature

In the last module you saw that the maximum height of the sun in the sky changes over the course of the year in a way that is very similar to the annual changes in temperature. In this module you will look at the relationship between height of the sun in the sky and temperature at a given place.

Relationship Between Height of the Sun in the Sky and Temperature

Are temperature and the height of the sun in the sky at a given place related? In this activity you will look at average daily temperature and the height of the sun in the sky for 12 specific dates in Chicago, IL to find out.

In previous modules the graphs showed how both temperature and height of the sun in the sky changed over time in a repeating up and down manner throughout the year. The graphs showed a repeating pattern because of the movement of the earth around the sun.

In this activity, you will graph the relationship between two variables (temperature and height of the sun in the sky) both of which change over time. The map above pinpoints Chicago, IL.

The table above shows data from Chicago for 12 specific dates. For each date, the data you see in the "Average temperature" and "Daily recorded energy from the sun" is averaged over a period of 30 years. Data in the other columns does not change from year to year. You can hover over the column headers for a description of each data type.

Select columns in the table in the following order: Click first at the top of the "Maximum height of sun in sky" column to highlight it in red; then click at the top of the "Average temperature" columns to highlight them in blue. If you make a mistake and the colors are switched, you can re-click to unselect and try again.

The graph shown is called a scatterplot. Each point represents a value for the two variables you highlighted in the table. Data for the first variable you selected will always be shown on the X-axis, and data for the second variable will always be shown on the Y-axis. This graph tells you what the average daily temperature is when the maximum height of the sun in the sky has a particular value.

Click on Line of Best Fit at the bottom right corner of the graph.

The line that runs through the points on the scatterplot is called a line of best fit. It represents the linear (straight-line) relationship between the two variables. It tells you how the maximum height of the sun in the sky and average daily temperature are related and gives you an estimate of what the temperature might be when you know what the maximum height of sky is.

This graph shows that at the times of the year when the maximum height of the sun in the sky is greater, the temperature in Chicago tends to be warmer, and at the times of the year when the sun is lower in the sky, the temperature tends to be cooler. This is because when the sun is higher in the sky, a greater amount of the sun's energy reaches the earth at that location, heating the air and the earth.

You will now have a chance to explore the relationship between the height of the sun in the sky and average daily temperature at locations and dates of your choosing. See whether other locations show the same relationship between the maximum height of the sun in the sky and average daily temperature that you saw in Chicago.

Try It: Height of the Sun in the Sky and Temperature

1. Click on the map to choose a location anywhere in the world.

2. Open the calendar and choose at least ten dates scattered throughout the year. Click on the the calendar for each new date you want to choose.

3. To create a graph, click first on the column in the table showing maximum height of the sun in the sky and then on the column showing average daily temperature. You can hover over the column headers for a description of each data type.

4. Click "Line of Best Fit" at the bottom right corner of the graph.

5. Repeat this activity for as many locations as you like. You can push the red button to reset your dates and markers.

Module Complete

Quiz Yourself:

  • What happens to the average daily temperature at a location as the maximum height of the sun in the sky at that location increases?
  • Why is the relationship between the maximum height of the sun in the sky and average daily temperature called a linear relationship?

Expand Your Knowledge:

Use the Seasons Simulator, to see how the height of the sun in the sky is related to average temperature.

Hours of Daylight

In the last module you saw that there is a relationship between the height of the sun in the sky and temperature. At times of the year when the sun is high in the sky it tends to be warmer, and at times of the year when the sun is lower in the sky it tends to be cooler.

In this module you will examine how the number of hours of daylight (the hours between sunrise and sunset) changes at different places over the course of a year.

"Sunset at Halong Bay" by Ha Long Bucht [CC-BY-SA-2.0], via Wikimedia Commons

Exploring Daylight

In the next four activities you will look at how the number of hours of daylight changes at four different locations (New York City, Plattsburgh, NY, and locations in Colombia and Ecuador) over the course of a year.
The map above pinpoints New York City.
The graph shows the number of hours of daylight in New York City for a two-year period, from January 1, 2003 to January 1, 2005.
You can see the exact number of hours of daylight on any particular day by hovering over different parts of the line on the graph with your cursor.
Notice that the number of hours of daylight each day changes throughout the year at this location. On the first day of fall (September 22) there are about 12 hours of daylight, on days in late June there are about 15 hours of daylight, and in late December there are just over 9 hours of daylight each day.
Also notice that the line is not jagged like the line for temperature was in Module B. The change in the number of hours of daylight is about the same from day to day.
Remember that we are talking about hours of “daylight,” not hours of “sunlight.” Because some days are rainy or cloudy and others are clear, there are big changes in the number of hours of sunlight each day, but the time the sun rises and sets changes very gradually from day to day.
Remember that when you looked at the graph for temperature, there was variation not only from day to day but also from year to year. Is that also true for the number of hours of daylight? What do you notice about the change in number of hours of daylight at a place on a particular date (for example, October 1st) from one year to the next?
What you should see is that the number of hours of daylight does not change from year to year. There are the same number of hours of daylight on October 1st, no matter what year it is.

Daylight Farther From the Equator

Now we are going to see what happen to the number of hours of daylight when we look at a place that is north of New York City. Plattsburgh, NY, which is about 300 miles north of New York City, is pinpointed on the map.

The two lines show the number of hours of daylight for Plattsburgh over a one-year period along with the hours of daylight for New York City.

Notice that in late December there are only 8.8 hours of daylight in Plattsburg, a little less than the 9.2 hours for the same time period in New York City. But in late June, there are 15.6 hours of daylight in Plattsburgh, a little more than the 15.1 hours in New York City.

Daylight Closer to the Equator

Now we are going to see what happens to the number of hours of daylight when we look at a place that is quite a bit south of New York City.

The place we have chosen is in Colombia in South America.

Notice how flat the line on the graph is? In late December there are just a little less than 12 hours of daylight, and in late June, there are just a little more than 12 hours of daylight. In late March (the first day of spring) and in late September (the first day of fall), there are 12 hours of daylight, just as there are in New York City.

Another way to describe the difference in the number of hours of daylight at these different places is to say that the range of daylight hours is different from place to place. The annual range of daylight hours in Colombia, which is near the equator in South America, is very small; the range is quite a bit larger in New York City; and larger yet in Plattsburgh, NY.

Daylight at the Equator

Now let’s look at one more place before you start to experiment yourself with different locations.

This time we are going to look at a place in Ecuador, very close to the equator.

Notice that the line is completely flat. There are 12 hours of daylight at this location in Ecuador all year long. In other words, there is no variation in the number of daylight hours.

Of course, the amount of sunlight at any location can change from day to day. Some days are cloudy and some days are sunny, but beause the sun rises and sets at the same time each day at the equator, the number of hours of daylight at the equator is always the same.
Only when you move north or south of the equator do you notice a change in the number of daylight hours throughout the year.

You will now have a chance to compare the number of hours of daylight throughout the year at two different locations of your choice. See if the range of daylight hours gets smaller the closer a place is to the equator and larger the farther a place is from the equator.

Try It: Daylight at Two Locations

1. Choose a range of dates that covers between two and three years. Click on the "Start" calendar to choose a starting date and the "End" calendar to choose an ending date.

2. Choose two locations to create a graph to see the difference in the number of hours of daylight at those two locations. If you select a place that is very far north or very far south (within about 1500 miles of the north or south poles), you will see that at some times of the year the number of hours of daylight at that place is zero and at other times of the year there is daylight all day long.

3. Repeat the activity as many times as you like before moving on to the next activity. You can push the red button to reset your dates and markers.

Module Complete

Quiz Yourself:

  • During what months of the year do places in the United States experience the greatest number of hours of daylight? Is that true everywhere in the world?
  • During what months of the year do places in the United States experience the least number of hours of daylight? Is that true everywhere in the world?
  • What happens to the range of daylight hours the closer a place is to the equator?
  • What happens to the range of daylight hours as you get close to the north or south poles?

Expand Your Knowledge:

Use the Daylight Hours Explorer, to see an animation showing how much daylight different parts of the earth experience throughout the year.

Hours of Daylight and Temperature

In the last module you saw that the hours of daylight at a location changes over the course of the year in a way that is very similar to the pattern for changes in temperature and maximum height of the sun in the sky. You have also seen that there is a relationship between the maximum height of the sun in the sky and temperature. During the parts of the year when the sun is higher in the sky, it tends to be warmer.

In this module you will look more closely at the relationship between the number of hours of daylight and the temperature at a given place. You will see if the two variables are related.

Comparing Hours of Daylight and Temperature

Are temperature and the number of hours of daylight at a given place related? In this activity you will look at average daily temperature and the number of hours of daylight for 12 different dates in Chicago, Illinois to find out.

The map above pinpoints Chicago, IL.

The table above is the same one you used in Module G. It shows data from Chicago averaged over a 30-year period for 12 specific dates.

Select columns in the table in the following order: click first on top of the "Hours of daylight" column to highlight it in red; then click on the top of the "Average temperature" column to highlight it in blue. If you make a mistake and the colors are reversed, you can re-click to unselect and try again.

Just as you saw in module G, the graph you see here is called a scatter plot. Each point represents a value for the two variables.

Click Line of Best Fit at the bottom right corner of the page.

The line of best fit that you see going through the scatterplot represents the linear (straight-line) relationship between the two variables you selected in the table. It shows you how the number of hours of daylight and the average daily temperature are related and allows you to estimate what the average temperature might be if you know the hours of daylight.

You can see from this graph that during the time of the year when the days are longer, the temperature tends to be warmer, and during the time of year when the days are shorter, the temperature tends to be cooler. This makes sense because the longer the day, the more time there is for the earth and the air around the earth to absorb energy from the sun.

You will now have a chance to explore the relationship between the hours of daylight and average daily temperature at locations of your choosing. See if there is a relationship between the hours of daylight and average daily temperature at other locations.

Try It: Hours of Daylight and Temperature

1. Choose a location anywhere in the world.

2. Open the calendar and choose at least ten dates scattered throughout the year.

3. First click on Hours of daylight and then click on Average daily temperature at the top of the table.

4. Click "Line of Best Fit" at the bottom of the page.

5. Repeat this activity for as many locations as you like before moving on to the next activity. You can push the red button to reset your dates and markers.

Module Complete

Quiz Yourself:

  • What happens to the average temperature at a location as the hours of daylight increase?
  • Why is the relationship between the number of hours of daylight at a location and the average temperature at that location called a linear relationship?

Expand Your Knowledge:

Find out how the sun's path in the sky, is related to the number of daylight hours.

Additional Data Tools

In this section you can use tools to continue to find patterns in data and explore the causes of some patterns you previously identified. Some of these tools were developed at AAAS, and others were developed at the University of Nebraska-Lincoln (UNL). The UNL tools require Adobe Flash player.


Data Finder
You can use the Data Finder to compare data averaged over 30 years for two locations on the same day.

Variable Relationship Explorer
Use the Variable Relationship Explorer when you want to make a scatter plot of two weather variables of your choosing to see how they are related to each other.

Daylight Hours Explorer
Use the UNL Daylight Hours Explorer when you want to visualize how the number of hours of daylight changes throughout the year at different degrees of latitude.

Seasons Simulator
Use the UNL Seasons Simulator to see how the earth's position relative to the sun changes in a regular pattern throughout the year and causes many of the patterns you previously explored.

Latitude and Longitude Demonstrator
Use the UNL Latitude and Longitude Demonstrator to see how the position of any place on earth can be described using geographic coordinates.

Data Finder

1. To see a table of data averaged over 30 years for a given location on a particular day, first select a location, and then choose a date.

2. To compare data for two locations on the same day, select a second location. You will see that the data for the second location appears in a separate column next to the data for the first location.

3. You can keep adding new locations, but only two locations will be shown in the table at any one time.

4. To choose two new locations and a new day, click on the red reset button and start over.

Variable Relationship Explorer

You used the Variable Relationship Explorer in Modules G and I to see how average daily temperature was related to both the height of the sun in the sky and the number of hours of daylight at a particular place.

You may have noticed that the Variable Relationship Explorer provided two additional columns of data for each location--the daily recorded energy from the sun and the daily theoretical energy from the sun. You will now have a chance to explore these variables too.

1. Choose a location anywhere in the world.

2. Open the calendar and choose at least 10 dates scattered throughout the year.

3. Decide which two variables you would like to compare from those five variables listed at the top of the columns.

4. First click at the top of the column of the variable you would like to be on the X-axis.

5. Next, click at the top of the column of the variable you would like to be on the Y-axis.

6. Is there a relationship between the two variables?

Daylight Hours Explorer

flash animation

The Daylight Hours Explorer lets you view the number of hours of daylight throughout the year at different degrees of latitude.

Use the sliding bars in the Settings box in the upper right corner to select a specific degree of latitude and a specific day of the year. The point that is marked on the graph represents the number of hours of daylight for the latitude and day of the year you selected.

The yellow line on the globe in the lower right corner shows the latitude that you have chosen.

Now use the slider bar to choose a latitude that is closer to the equator. What happens to the range in the number of daylight hours throughout the year as you get closer to the equator?

Just as you saw in Module H, the closer a location is to the equator, the smaller the range in the number of daylight hours that location has throughout the year.

Choose a latitude farther from the equator. What happens to the range in the number of daylight hours?

Just as you saw in Module H, the farther a location is from the equator, the larger the range in the number of daylight hours it has throughout the year.

Seasons Simulator

flash animation

You can use the Seasons Simulator to show how the changing position of the earth and sun throughout the year changes the angle at which the sun's rays hit the earth.

Click on "start animation" at the lower right of the simulator. Observe the changes on the screen. Click "stop animation" at any time.

Use the red slider on the calendar to change the date. Observe what happens to the position of the earth and the angle of the sun.

Click and drag the image of the earth on the left. Observe what happens to the angle of the sunlight on the stick figure and the place where the sun is directly overhead.

Click and drag the stick figure to change its latitude. Observe how the angle of the sunlight on the stick figure changes.

Continue to explore relationships between time of year, position of the stick figure, and the angle at which the sun strikes the earth and the stick figure.

Latitude and Longitude Demonstrator

flash animation

The Latitude and Longitude Demonstrator will give you practice describing the location of a place in terms of two numbers. One of the numbers is a measure of how far the place is north or south of the equator (latitude), and the other is a measure of how far a place is east or west of the prime meridian (longitude). Knowing how to describe a place in terms of its latitude and longitude will come in handy as you work through these activities because that is how a place's location is identified in these materials.

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