key term - Absorption Lines

Definition

Absorption lines are dark lines that appear in the continuous spectrum of light emitted by a hot object, such as a star. These lines are caused by the absorption of specific wavelengths of light by atoms in the cooler outer layers of the object, which selectively absorb certain frequencies of the emitted light.

5 Must Know Facts For Your Next Test

1. Absorption lines are caused by the selective absorption of specific wavelengths of light by atoms in the cooler outer layers of a hot object, such as a star.
2. The pattern of absorption lines in the spectrum of a star can be used to identify the elements present in the star's atmosphere, as each element has a unique set of absorption lines.
3. The Bohr model of the atom explains the formation of absorption lines by describing how electrons can only occupy certain discrete energy levels, and the absorption of light occurs when electrons transition to higher energy levels.
4. The width and depth of absorption lines can provide information about the temperature, density, and motion of the absorbing atoms in the object's atmosphere.
5. Absorption lines are a key feature of the solar spectrum and are used to study the composition and properties of the Sun's atmosphere.

Review Questions

• Explain how absorption lines are formed in the spectrum of a star.
  • Absorption lines in the spectrum of a star are formed when the continuous spectrum of light emitted by the hot, inner layers of the star passes through the cooler, outer layers of the star's atmosphere. The atoms in the outer layers selectively absorb specific wavelengths of light, corresponding to the energy levels of the electrons in those atoms. This selective absorption results in dark, or absorption, lines in the continuous spectrum, which can be used to identify the elements present in the star's atmosphere.
• Describe the relationship between absorption lines and the Bohr model of the atom.
  • The Bohr model of the atom explains the formation of absorption lines by describing how electrons can only occupy certain discrete energy levels within an atom. When an electron in an atom absorbs a photon of light with the exact energy required to transition to a higher energy level, the atom will absorb that specific wavelength of light, resulting in an absorption line in the spectrum. The pattern of absorption lines in a spectrum can therefore be used to identify the elements present in the object, as each element has a unique set of energy levels and corresponding absorption lines.
• Analyze how the properties of absorption lines can be used to study the characteristics of a star's atmosphere.
  • The properties of absorption lines in a star's spectrum can provide valuable information about the composition, temperature, density, and motion of the star's atmosphere. The width and depth of the absorption lines can indicate the temperature and density of the absorbing atoms, while the position of the lines can reveal the radial velocity of the star's atmosphere due to the Doppler effect. Additionally, the specific pattern of absorption lines can be used to identify the elements present in the star's atmosphere, which is crucial for understanding the star's composition and evolution. By analyzing the absorption line spectrum, astronomers can gain deep insights into the physical and chemical properties of a star's outer layers.

Related terms

Emission Lines: Emission lines are bright lines that appear in the spectrum of light emitted by a hot, rarefied gas. These lines are caused by the emission of specific wavelengths of light by atoms as they transition between energy levels.

Continuous Spectrum: A continuous spectrum is a spectrum of light that contains all wavelengths without any gaps or discontinuities, as opposed to a line spectrum, which consists of discrete, isolated lines.

Bohr Model:

The Bohr model is a representation of the atom, in which electrons orbit the nucleus in discrete energy levels, and the absorption or emission of light is due to electrons transitioning between these energy levels.