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🪐intro to astronomy review

Transverse Velocity

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

Definition

Transverse velocity is the component of an object's velocity that is perpendicular to the line of sight. It is a crucial parameter in understanding the motion of celestial bodies, particularly in the context of using spectra to measure stellar radius, composition, and motion.

5 Must Know Facts For Your Next Test

  1. Transverse velocity is an important parameter in determining the size of a star, as it can be used in conjunction with the star's angular diameter to calculate its true physical diameter.
  2. The transverse velocity of a star, combined with its distance from the observer, can be used to calculate the star's proper motion, which is the apparent motion of the star across the sky.
  3. Spectroscopic binary stars exhibit changes in their spectral lines due to the orbital motion of the two stars, which includes both their transverse and radial velocities.
  4. Measuring the transverse velocity of a star can provide information about its composition, as different elements in the star's atmosphere will have different transverse velocities due to their atomic masses.
  5. Transverse velocity is a key parameter in understanding the overall motion of a star, as it represents the component of the star's velocity that is perpendicular to the observer's line of sight.

Review Questions

  • Explain how transverse velocity is used to measure the physical size of a star.
    • Transverse velocity, in combination with a star's angular diameter, can be used to calculate the star's true physical diameter. The angular diameter of a star represents the apparent size of the star in the sky, while the transverse velocity represents the component of the star's motion that is perpendicular to the observer's line of sight. By knowing both the angular diameter and the transverse velocity, the star's true physical size can be determined using the formula: Physical Diameter = (Angular Diameter × Distance) / Transverse Velocity.
  • Describe how transverse velocity is used to determine the proper motion of a star.
    • The proper motion of a star is the apparent motion of the star across the sky, which is a combination of the star's transverse velocity and its distance from the observer. By measuring the transverse velocity of a star and knowing its distance, the component of the star's motion that is perpendicular to the line of sight can be calculated. This transverse velocity, along with the star's radial velocity (the component of the velocity parallel to the line of sight), can then be used to determine the star's overall proper motion, which is an important parameter in understanding the kinematics of stellar systems.
  • Explain the role of transverse velocity in the analysis of spectroscopic binary stars.
    • Spectroscopic binary stars are binary systems where the individual stars cannot be resolved visually, but their orbital motion can be detected through changes in their spectral lines. These changes in the spectral lines are influenced by both the transverse and radial velocities of the stars. The transverse velocity component represents the portion of the stars' orbital motion that is perpendicular to the observer's line of sight, while the radial velocity component represents the portion that is parallel to the line of sight. By analyzing the variations in the spectral lines, astronomers can infer the transverse and radial velocities of the binary system, which in turn provides information about the stars' orbits, masses, and other fundamental properties.