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🪐intro to astronomy review

K-type Star

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

A K-type star, also known as an orange dwarf, is a class of main-sequence stars that are cooler, less massive, and less luminous than the Sun. These stars have surface temperatures ranging from around 3,700 to 5,200 Kelvin and are characterized by their distinctive orange-red hue.

5 Must Know Facts For Your Next Test

  1. K-type stars are the second-coolest class of main-sequence stars, with surface temperatures ranging from 3,700 to 5,200 Kelvin.
  2. K-type stars are less massive and less luminous than the Sun, with masses ranging from about 0.45 to 0.8 times the mass of the Sun.
  3. These stars have a longer lifespan than the Sun, with typical lifetimes of 15 to 30 billion years.
  4. K-type stars are commonly used as standard candles in the cosmic distance ladder, as their intrinsic luminosities can be estimated based on their spectral types.
  5. The location of K-type stars on the Hertzsprung-Russell (H-R) diagram is in the orange-red region, just to the right of the Sun's position.

Review Questions

  • Explain how the properties of K-type stars, such as their surface temperature and luminosity, are related to their position on the H-R diagram.
    • K-type stars are located in the orange-red region of the Hertzsprung-Russell (H-R) diagram, which represents stars with lower surface temperatures (3,700 to 5,200 Kelvin) and lower luminosities compared to the Sun. Their position on the H-R diagram is a direct reflection of their physical properties, with cooler surface temperatures resulting in a lower energy output and less luminous appearance. The H-R diagram allows astronomers to categorize and understand the relationship between a star's temperature, luminosity, and other fundamental characteristics.
  • Describe how the use of K-type stars as standard candles contributes to the cosmic distance ladder and the determination of distances to celestial objects.
    • K-type stars are commonly used as standard candles in the cosmic distance ladder, a set of techniques used to measure the distances to increasingly remote objects in the universe. Since the intrinsic luminosity of K-type stars can be estimated based on their spectral type, astronomers can compare the observed brightness of a K-type star to its known luminosity to calculate its distance from Earth. This method, known as the absolute magnitude-apparent magnitude relationship, is a crucial step in the cosmic distance ladder, allowing astronomers to determine the distances to galaxies and other distant objects by using the known properties of K-type stars as a reference point.
  • Analyze the significance of the longer lifespan of K-type stars compared to the Sun and explain how this feature contributes to their usefulness in studying the evolution of the universe.
    • The longer lifespan of K-type stars, typically ranging from 15 to 30 billion years, is a significant factor in their importance for studying the evolution of the universe. Unlike the Sun, which has a relatively short main-sequence lifetime of around 10 billion years, K-type stars can remain stable for much longer periods. This extended lifetime allows them to serve as 'cosmic clocks,' providing a longer window of observation for astronomers to study the processes and changes that occur in stellar systems and galaxies over time. The longevity of K-type stars makes them valuable probes for understanding the long-term evolution of the universe, as they can offer insights into the early stages of galaxy formation and the chemical enrichment of the cosmos.