# Red/blueshift due to orbiting planet

• tumconn
In summary, the conversation discusses the periodical oscillations of a star's spectral lines, indicating the presence of a planet with a period of 2.1375 days. The task at hand is to calculate the observed wavelengths of the NaI double line, given the star's mass of 1.2 solar masses and the assumption that the planet's mass is negligible and its orbit is circular. Although the Doppler effect is mentioned as a possible explanation for the shift in wavelength, it is determined that it cannot be applied in this scenario.
tumconn

## Homework Statement

The periodical oscillations of the spectral lines of a star incicate that there is a planet orbiting around it with a period of 2.1375 days.Calculate what the observed wavelengths of the NaI double line will be,which is normally observed at 586.6nm and 589.6nm.
Star's mass=1.2 solar masses
Assume the planet's mass is negligible compared to the mass of the star and that its orbit is circular.

Kepler's law
Doppler effect

## The Attempt at a Solution

I would guess the shift in wavelength is because the gravitational force acting on the star because of the planet's mass at the points radially away from the earth,cause the star to move with a miniscule speed u,resulting in a red/blueshift.
But,firstly, I can't calculate the mass of the planet in order to get the star's acceleration
and secondly,even if I did,the phrase "Assume the planet's mass is negligible" leads me to believe this is not the correct solution.

You are right. If the planet's mass is negligible, then there is no Doppler shift. Whoever wrote the problem is confused.

tumconn

## What is red/blueshift due to orbiting planet?

Red/blueshift refers to the change in the frequency of light emitted by a source, caused by the relative motion between the source and the observer. When an orbiting planet moves towards the observer, the light from the source appears to have a higher frequency, resulting in a blueshift. Conversely, when the planet moves away from the observer, the light appears to have a lower frequency, resulting in a redshift.

## What causes red/blueshift due to orbiting planet?

The red/blueshift due to orbiting planet is caused by the Doppler effect, which is the change in the perceived frequency of sound or light waves due to the relative motion between the source and the observer. In the case of an orbiting planet, its motion causes the light waves to either compress or stretch, resulting in a change in frequency.

## How is red/blueshift due to orbiting planet measured?

The red/blueshift due to orbiting planet can be measured using spectroscopy, a technique that analyzes the wavelengths of light emitted by an object. By comparing the observed wavelengths to the expected wavelengths, scientists can determine the amount of red/blueshift and therefore, the speed and direction of the orbiting planet.

## What factors can affect the amount of red/blueshift due to orbiting planet?

The amount of red/blueshift due to orbiting planet can be affected by various factors, such as the mass and velocity of the orbiting planet, the distance between the planet and the observer, and the angle of the planet's orbit relative to the observer's line of sight. Additionally, the gravitational pull of other nearby objects can also impact the red/blueshift measurements.

## How is the knowledge of red/blueshift due to orbiting planet useful in astronomy?

The red/blueshift due to orbiting planet can provide important information about the motion and characteristics of orbiting planets, such as their mass, velocity, and distance from their parent star. This knowledge can help astronomers to better understand the dynamics of planetary systems and make predictions about the formation and evolution of these systems.

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