# Comment on "The relativistic Doppler effect: when a zero-frequency ..."

## TL;DR

This paper critiques a previous work on the relativistic Doppler effect, identifying and correcting errors related to the equations used, thereby clarifying the correct interpretation of frequency shifts for approaching sources.

## Contribution

It provides a correction to prior faulty conclusions by addressing errors in the equations used in the original analysis of the relativistic Doppler effect.

## Key findings

- Corrects the erroneous equations in the previous paper
- Clarifies the conditions for zero-frequency and red shifts in relativistic Doppler effect
- Ensures accurate interpretation of frequency shifts for approaching sources

## Abstract

In the paper "The relativistic Doppler effect: when a zero-frequency shift or a red shift exists for sources approaching the observer, Ann. Phys. (Berlin) 523, No. 3, 239-246 (2011), DOI 10.1002/andp.201000099 by C. Wang the use of an erroneous equation ended up at a number of faulty conclusions which are corrected in the present Comment.