Velocity correction´ formula for the rotation of the Earth

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Discussion Overview

The discussion revolves around the velocity correction formula for measuring spectral lines from the Sun, specifically in the context of the Earth's rotation and its effects on observed velocities. Participants explore the contributions of both the Earth's rotation and the Sun's rotation, as well as the influence of solar wind on these measurements.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether the velocity correction formula accounts for the Sun's rotational velocity components alongside the Earth's, suggesting that both velocities may affect measurements depending on their angles.
  • Another participant notes that the Earth's equatorial rotation speed is about 2 km/s, while the equatorial radial velocity is 0.464 km/s, arguing that neglecting the Sun's rotation would lead to inaccurate calculations unless averaging the flux across the entire solar disc.
  • It is mentioned that the eccentricity of the Earth's orbit can produce additional radial velocities of up to 0.5 km/s over the course of a year.
  • A participant inquires about calculating the solar wind contribution to the line of sight, referencing a typical speed of 400 km/s for solar wind near Earth.
  • Another participant suggests a method for calculating the solar wind contribution by multiplying the wind speed by the cosine of the angle between the wind direction and the line of sight.

Areas of Agreement / Disagreement

Participants express differing views on the significance of the Sun's rotational contribution to the velocity correction formula, indicating that multiple competing views remain regarding the factors that should be considered in the calculations.

Contextual Notes

Participants have not fully resolved the implications of the Earth's eccentric orbit on velocity measurements, nor have they reached a consensus on the necessity of including the Sun's rotational velocity in the correction formula.

Who May Find This Useful

This discussion may be of interest to those studying astrophysics, particularly in the areas of spectral analysis and the effects of celestial mechanics on observational data.

Ennio
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TL;DR
Does the velocity correction´s formula for rotation of the Earth include Sun contributes?
Let´s suppose we are observing the sun and measuring some spectral lines.

Does the velocity correction´s formula for the Earth include the rotational velocity components of the Sun as well?
or rather
are we basically measuring both velocity contributes of Earth and of Sun together (receeding or approachning depending of course from the angles) ?

v= 0.464 * sin(H) * cos(D) * cos (L) [Km/sec]

0.464 Km/sec is the equatorial radial velocity of Earth
H: hour angle of the Sun [deg]
D: declination of the Sun [deg]
P: Earth latitude of the observatory [deg]

Thanks in advance for your support
 
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Run rotation speed at equator is about 2 km/s while Earth is only 0.46 km/s. Neglecting contribution of Sun` rotation would be a bad calculation, unless you averaging flux across whole disc of Sun. Also, Earth orbit is eccentric, which produce up to 0.5 km/s radial velocities with period of one year.
 
trurle said:
Run rotation speed at equator is about 2 km/s while Earth is only 0.46 km/s. Neglecting contribution of Sun` rotation would be a bad calculation, unless you averaging flux across whole disc of Sun. Also, Earth orbit is eccentric, which produce up to 0.5 km/s radial velocities with period of one year.

Hi @trurle, thank you very much. Do you know how to calculate the solar wind contribution in the line of sight? I have read it is 400Km/sec
 
Ennio said:
Hi @trurle, thank you very much. Do you know how to calculate the solar wind contribution in the line of sight? I have read it is 400Km/sec
Just multiply by cosine between wind direction (outward) and line of sight. 400 km/s is typical for vicinity of Earth indeed.
 

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