Discussion Overview
The discussion revolves around the measurement of distances to galaxies using redshift, specifically focusing on how to determine the source wavelength necessary for calculating recessional velocity. The scope includes theoretical aspects of redshift and practical considerations in astrophysics.
Discussion Character
- Exploratory
- Technical explanation
- Conceptual clarification
Main Points Raised
- One participant questions how to know the source wavelength needed for calculating recessional velocity using the redshift formula.
- Another participant explains that different elements have distinctive spectral lines with known wavelengths that can be measured in the lab, which can help identify the source wavelength.
- A subsequent post reiterates the idea of distinctive spectral lines and suggests that knowledge of the elements constituting galaxies allows for the determination of source wavelengths.
- Further, a participant emphasizes that the abundance of hydrogen and helium in the universe makes it easier to identify spectral lines, comparing them to a fingerprint or face pattern, and notes the consistency of shifts in these lines.
Areas of Agreement / Disagreement
Participants generally agree on the importance of distinctive spectral lines for identifying source wavelengths, but there is no consensus on the implications or completeness of this method in all contexts.
Contextual Notes
The discussion does not address potential limitations in identifying source wavelengths for less common elements or in more distant galaxies where spectral lines may be less clear.
is how we can know the source wavelength.