key term - Absorption Lines

Definition

Absorption lines are dark lines that appear in the spectrum of a star or other celestial object, representing wavelengths of light that have been absorbed by atoms or molecules in the object's atmosphere. These lines provide valuable information about the chemical composition and physical properties of the object.

5 Must Know Facts For Your Next Test

1. Absorption lines are caused by the selective absorption of specific wavelengths of light by atoms or molecules in the atmosphere of a star or other celestial object.
2. The pattern of absorption lines in a star's spectrum is unique and can be used to identify the chemical elements present in the star's atmosphere.
3. The strength and width of absorption lines can provide information about the temperature, pressure, and density of the stellar atmosphere.
4. Absorption lines can also be used to measure the radial velocity of a star or other celestial object through the Doppler shift of the lines.
5. Interstellar matter between the observer and the celestial object can also produce absorption lines, providing information about the composition and physical properties of the intervening material.

Review Questions

• Explain how absorption lines are formed in the spectrum of a star and how they can be used to determine the star's chemical composition.
  • Absorption lines are formed when atoms or molecules in the star's atmosphere selectively absorb specific wavelengths of light, creating dark lines in the star's spectrum. These absorption lines are unique to the chemical elements present in the star's atmosphere, and by analyzing the pattern of absorption lines, astronomers can determine the chemical composition of the star. The strength and width of the absorption lines can also provide information about the temperature, pressure, and density of the stellar atmosphere.
• Describe how absorption lines can be used to measure the radial velocity of a star and how this information is used in the study of stellar motion and evolution.
  • Absorption lines in a star's spectrum can be used to measure the star's radial velocity, or the component of its motion along the line of sight, through the Doppler shift of the lines. If the star is moving away from the observer, the absorption lines will be shifted towards longer (red) wavelengths, while if the star is moving towards the observer, the lines will be shifted towards shorter (blue) wavelengths. By measuring the Doppler shift of the absorption lines, astronomers can calculate the star's radial velocity, which is an important parameter in understanding the star's motion and evolution within the galaxy.
• Explain how absorption lines in the spectrum of a celestial object can provide information about the interstellar matter between the object and the observer, and discuss the significance of this information in the study of the structure and composition of the Milky Way galaxy.
  • Absorption lines in the spectrum of a celestial object can be caused not only by atoms and molecules in the object's own atmosphere, but also by interstellar matter between the object and the observer. These interstellar absorption lines can provide valuable information about the composition, density, and physical properties of the intervening material, which is important for understanding the structure and composition of the Milky Way galaxy. By analyzing the pattern and characteristics of these interstellar absorption lines, astronomers can map the distribution of various elements and molecules in the galaxy, as well as study the dynamics and evolution of the interstellar medium, which is a crucial component in the formation and evolution of stars and galaxies.

Related terms

Emission Lines:

Emission lines are bright lines that appear in the spectrum of a celestial object, representing wavelengths of light that have been emitted by atoms or molecules in the object's atmosphere or surrounding environment.

Fraunhofer Lines:

Fraunhofer lines are a series of absorption lines in the solar spectrum, named after the German physicist Joseph von Fraunhofer, who first observed and cataloged them in the early 19th century.

Doppler Shift:

Doppler shift is the change in the observed wavelength of light due to the relative motion between the source and the observer, which can be used to measure the radial velocity of a star or other celestial object.