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Introduction to Stars

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Introduction to Stars

You are helping a science team explain how stars work. Read the mini-brief, then use evidence and science ideas to solve each task. Show your reasoning where asked.

Star briefing

Stars are enormous spheres of hot plasma held together by gravity. Most are made mainly of hydrogen and helium. Deep in a star’s core, pressure and temperature are so high that nuclear fusion can occur. In the Sun and other stars like it, hydrogen nuclei combine through a series of reactions that ultimately produce helium. A small amount of mass is converted into energy, which travels outward and is emitted as light and other forms of radiation. A star’s luminosity is the total energy it emits each second. It is not the same as how bright the star appears from Earth: distance also affects apparent brightness. Stars change over time, and their paths depend strongly on their initial mass. Elements heavier than helium are formed through stellar processes and are spread into space by stellar winds and, for some stars, explosive events. Later generations of stars and planets can form from this enriched material.

Decode the star

Use the briefing to answer.

1.Which description best explains what a star is?

A solid ball of rock that reflects nearby light
A sphere of hot plasma held together by gravity that emits energy
A planet that shines because it orbits a star
A cloud of cold gas with no internal energy source

2.Complete the chain: In a Sun-like star, hydrogen nuclei undergo nuclear , ultimately forming and releasing energy.

3.Match each term to its meaning.

Luminosity
Fusion
Plasma
Gravity

Process in which atomic nuclei combine
Attractive force that helps hold a star together
Hot matter made of charged particles
Total energy emitted by a star each second

4.A star is much farther from Earth than another star, but both have the same luminosity. Which statement is most likely true about how they appear from Earth?

The farther star appears dimmer
The farther star appears brighter
They must appear equally bright
Distance cannot affect apparent brightness

5.A student says, “Fusion happens at the star’s surface because that is where we see light escaping.” Identify the error and correct the explanation using the star briefing.

Evidence and consequences

Apply the ideas to the star team's investigation.

6.A data team compares two stars. Star A emits 8 units of energy each second and Star B emits 3 units each second. Which has greater luminosity, and by how many units per second?

7.True or false: A star that looks brighter in our sky must have a greater luminosity than every star that looks dimmer. Explain your choice.

8.Explain how stars help supply the ingredients for future stars, planets, and living things. Include how heavier elements enter space.

9.Why is “cosmic furnace” a useful comparison for a star? Give one way the comparison works and one way it could be misleading.

10.A research team argues that the Sun matters to Earth only because it makes daylight. Give two other ways the Sun or stars are important to Earth or the wider universe.