Reading and Interpreting a Line Graph
What is a Line Graph?
A line graph is a tool that provides a picture using a line or lines to show how things change over time or how they're connected. For instance, you want to see how a plant grows over time. So you measure the plant's height every week. You can use a line graph to see how the plant is growing!
Reading and Interpreting the Graph (See Figure 1.)
• Seeing Changes: Look at the line. If it goes up, the plant is growing! If it stays flat, it's not changing its height, and if the line goes down, the plant is losing height.
• Comparing Weeks: You can easily see which weeks the plant grew the most by looking for the steepest parts of the line.
Finding the Height (See Figure 2.)
• To find the plant height at a certain week, find that Week Number on the bottom line (x-axis), go straight up to the line, and then look across to the Plant Height number on the side (y-axis). On this graph, the plant at week 6 had a height of 9 centimeters.
Extrapolating the Data Beyond the Line (See Figure 3.)
• Following the Trend: If the line is going up or down steadily, you can predict that the plant will continue changing its height at about the same rate in the next few weeks.
• Making a Prediction: You can extend the line a little bit past your last data point (see the dashed line) to make a prediction about the plant's height in the future. But remember, it's just a prediction! Things might change.
Using our extended line in this graph, we predict the plant will have a height of 7 centimeters at week 11.
• Limitations: Extrapolating too far out is not always accurate. The plant could stop growing, or grow at a different rate.
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What is a star?
A star is a luminous ball of plasma held together by its own gravitational field. The elements that make up most stars are mainly hydrogen and helium in the plasma phase of matter. The nearest star to Earth is the Sun. Stars are the most common astronomical objects.
How do stars make light?
Stars use a nuclear reaction to make their own light. Stars fuse hydrogen atoms to form helium. In this process, huge amounts of energy are released. Some of this energy is released in the form of visible light. Other electromagnetic waves, such as radio, microwaves, X-rays, and gamma rays are also released during the fusion process.
How are stars classified?
Stars are classified in several different ways, such as by their mass, their radius, their luminosity, or their age. Most of the time using the first three classification systems, stars are compared to Earth’s Sun. For instance, the star Betelgeuse has a mass about 15 times greater than the Sun, a luminosity about 50,000 times brighter than our Sun, and over a 1,200 times greater solar radius than the Sun.
What is a solar radius?
The solar radius of a star is the average distance from the star’s center to its outermost edge.
What is luminosity?
Luminosity is the intrinsic brightness of a star and depends on the amount of energy emitted from the star each second.
What is the difference between the apparent brightness and intrinsic brightness of a star?
The intrinsic brightness of a star is a measure of the total electromagnetic output of the star. This value does not significantly vary with the distance away from the star. The apparent brightness of a star is based on how bright a star appears in Earth’s sky and is directly impacted by the distance the star is away from Earth. The farther away from Earth, the dimmer the star.
What does Fc represent?
The abbreviation “Fc” stands for “foot-candle” and is a measure of the intensity of light. One Fc is the illumination of a one-foot radius sphere with a point source of one candela or lumen. A typical classroom has a light intensity of about 80 Fc.
How are stars classified by their temperature?
The brightness of a star is dependent on the temperature of the star. While hot stars are expected to be brighter than cooler stars, the color of the light emitted by the star is a good measure of the star’s temperature. The hottest stars appear blue, while the coolest stars are red. The frequency range of the visible part of the electromagnetic spectrum coincides with the temperature range of stars. The image below shows the average surface temperatures (measured in Kelvin) of stars and their common colors.
What is the Hertzsprung-Russell (H-R) diagram?
The H-R diagram is a tool used by astronomers to classify stars based on their history, age, function, and rate of mass loss. Using this system, stars are broadly classified into four main classes: giants, supergiants, main sequence, and white dwarfs. Stars are further classified on the diagram into various types using a letter system that indicates the evolution of the star. These types range from O, B, A, F, G, K, to M with type O being the youngest stars and M the oldest. A version of the H-R diagram appears below.
Why are some stars in the night sky brighter than other stars? Get started now investigating the causes of the apparent brightness of stars in the sky.)
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