The spectroscopic radial velocity method of planet discovery measures a motion that is most like the motion of a. a tetherball around a pole. b. Earth around its axis. c. a swinger on a swing. d. an ice-skater spinning his partner.

The Doppler effect is a phenomenon that occurs when there is a change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. This effect can be observed in sound waves, like when an ambulance siren changes pitch as it passes you, but it’s also critical in understanding light from stars in astronomy.

In the context of the radial velocity method, the Doppler effect causes the spectral lines of a star to shift back and forth. When a star moves towards us, its light waves get compressed, making the spectral lines move to shorter wavelengths (blue shift). When it moves away, the waves stretch out, making the lines move to longer wavelengths (red shift).

By carefully measuring these tiny shifts, astronomers can determine the star's velocity changes over time. This gives us clues about the presence of exoplanets since the star's wobble is influenced by the gravitational pull of orbiting planets.

Planet detection is a fascinating area of astronomy, where scientists try to discover planets outside our solar system, called exoplanets. The radial velocity method is one of the key techniques used for this purpose.

This technique involves detecting the small changes in a star's motion caused by an orbiting planet. As the planet orbits, it exerts a gravitational pull on the star, making the star move in a small orbit as well. This motion affects the star’s light through the Doppler effect, which we can measure.

Important points about the radial velocity method for planet detection:

• It helps identify various properties of exoplanets, such as their mass and orbit.
• Works best for large planets close to their stars since they create more noticeable effects.
• Complements other detection methods like transit photometry, where a planet passing in front of its star dims its light.

Using radial velocity, astronomers can detect planets even if they don't pass directly in front of their stars from our viewpoint.

Gravitational influence is a fundamental force that governs the interactions between objects with mass. In the context of the radial velocity method, the gravitational influence of an orbiting planet causes its host star to ‘wobble’.

Here’s a simple way to understand it: Imagine two dancers holding hands and spinning around each other. Both the dancers move around a common center of mass. In a similar fashion, both the star and the planet orbit their shared center of mass, causing the star to shift slightly in position.

Key aspects of gravitational influence in planet detection:

• The larger the planet, the stronger its gravitational pull on the star, leading to more significant velocity changes.
• The closer the planet to the star, the faster it can induce a detectable wobble.
• Even small planets cause measurable effects if we have precise enough instruments.

Understanding these gravitational interactions helps scientists infer many details about distant planetary systems.