Question 1: Define a main sequence star and explain the primary process that powers it.

Answer: A main sequence star is a star that is in the stable phase of hydrogen fusion in its core, which produces energy that balances gravitational collapse. The primary process powering it is nuclear fusion of hydrogen atoms into helium.

Question 2: List two key characteristics of stars during the main sequence phase.

Answer: They have a stable size and brightness, and their luminosity correlates with their surface temperature.

Question 3: A star has a surface temperature of 5800 K and a luminosity similar to the Sun. Based on the Hertzsprung-Russell diagram, what category does this star belong to?

Answer: Sun-like Main Sequence Star

Question 4: Explain how nuclear fusion in the core of a main sequence star maintains its stability.

Answer: Nuclear fusion converts hydrogen into helium, releasing energy in the form of light and heat. This energy creates outward pressure that balances the inward pull of gravity, maintaining the star's size and brightness during the main sequence phase.

Question 5: Using the formula for stellar luminosity: Luminosity (L) = 4πR²σT⁴, where R is the radius, σ is the Stefan-Boltzmann constant, and T is temperature, explain how a change in temperature affects a star’s luminosity.

Answer: Luminosity is proportional to the fourth power of temperature (T⁴). Therefore, even a small increase in temperature results in a significant increase in luminosity, while a decrease causes a substantial reduction.

Question 6: A star’s radius is doubled, and its surface temperature remains constant at 5800 K. How does its luminosity change?

Answer: Since luminosity is proportional to R², doubling the radius increases luminosity by a factor of 4.

Question 7: Identify and describe two variables that astronomers measure to determine if a star is in the main sequence phase.

Answer: Astronomers measure the star’s surface temperature and luminosity to determine if it follows the main sequence pattern on the Hertzsprung-Russell diagram.

Question 8: During the main sequence phase, what is the primary fuel used by stars like the Sun?

Answer: Hydrogen

Question 9: Multiple Choice: Which of the following is true for a star during the main sequence?

Answer: Hydrogen fusion is occurring in its core.

Question 10: Fill in the blank: The main sequence phase lasts for approximately __________ of a star’s lifetime.

Answer: 90%

Question 11: Describe one way in which understanding the main sequence phase is important for predicting the future evolution of stars.

Answer: Understanding the main sequence phase helps scientists predict when a star will exhaust its hydrogen fuel, leading to phases like red giant or supernova, and informs models of stellar evolution and the lifecycle of planetary systems.