How to calculate the wavelength of light coming from 1 light year away

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SUMMARY

The discussion focuses on calculating the wavelength of light from an object located one light year away. It clarifies that the wavelength is determined by the object's color, which can be affected by red or blue shifting due to relative motion. The Hubble expansion formula, represented as v = H0D, is applicable primarily to distant galaxies and not to nearby stars, which are influenced by local gravitational fields. The Doppler Formula is essential for measuring frequency shifts to determine relative motion between a star and Earth.

PREREQUISITES
  • Understanding of electromagnetic radiation and its spectrum
  • Familiarity with the Doppler Effect and its application in astronomy
  • Knowledge of Hubble's Law and its limitations
  • Basic concepts of gravitational binding in galaxies
NEXT STEPS
  • Research the Doppler Formula and its application in measuring stellar motion
  • Study Hubble's Law and its relevance to distant galaxies
  • Explore the concept of redshift and blueshift in astrophysics
  • Investigate the gravitational dynamics of local galaxy clusters
USEFUL FOR

Astronomers, astrophysics students, and anyone interested in understanding the behavior of light from distant celestial objects and the effects of motion on wavelength measurements.

shantanu23
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TL;DR
How to calculate the wavelength of light coming from 1 light year away.
Is there any formula for it.
How to calculate the wavelength of light coming from 1 light year away.
Is there any formula for it.

Please help.
 
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shantanu23 said:
Summary:: How to calculate the wavelength of light coming from 1 light year away.
Is there any formula for it.

How to calculate the wavelength of light coming from 1 light year away.
Is there any formula for it.

Please help.
I think you have a fundamental misunderstanding of light. "Light" is an English language term which is used either for (1) any frequency of electromagnetic radiation or for (2) that range of the electromagnetic spectrum which is in the visible by humans.

The wavelengths range from near zero to extremely high. If there is no proper motion between you and the 1 light year distant object, then the wavelength is just a measure of what in English is called the "color". If there IS proper motion then there can be red or blue shifting so that the wavelength you see is not exactly that emitted.
 
Are you talking about the Expansion of the Universe and the red shift here? A quick buzz through this wiki link will tell you what you need to know and the context.
The equation v = H0D tells you only the average speed of recession v for galaxies at distance D, due to the actual expansion of the space. That is only a ballpark figure because there will be motion of Earth relative to each galaxy.
If you measure the frequency of a spectral line in light from a galaxy, you can use the Doppler Formula to obtain v from the frequency shift relative to the spectrum of the elements on Earth.

The Hubble expansion formula doesn't apply to nearby stars - in our own galaxy - because they are constrained by the local gravitational field within the galaxy. H0 can only be used for galaxies because they are considered 'independent' of the mass of our galaxy. But you can tell the relative motion between a star and Earth by measuring the frequency shift (red or blue, depending)

It's down to what you actually describe as a galaxy (see this link and others) but the sort of distance between us and the nearest dense groups of stars is tens of thousands of light years and small galaxies in our local cluster are much further away than that. Hubble definitely can't tell you anything about the likely frequency shift at 1LY.
 
sophiecentaur said:
Hubble definitely can't tell you anything about the likely frequency shift at 1LY.
More than that, there is no effect from the expansion of the universe at this scale. Stars in a galaxy (or even the local group of galaxies) are gravitationally bound and are not receding due from us as more distant objects are. The relative motion of the star in its path around the galaxy is the only source of a Doppler shift.
 
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Ibix said:
More than that, there is no effect from the expansion of the universe at this scale. Stars in a galaxy (or even the local group of galaxies) are gravitationally bound and are not receding due from us as more distant objects are. The relative motion of the star in its path around the galaxy is the only source of a Doppler shift.
Which is why I responded the way I did, given that he was talking about only a 1 LY distance.
 
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