# How Can We Measure Redshift Using the Spectrum of a Star?

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• Phys12
In summary, by analyzing the spectrum of a star and looking at the absorption lines, we can detect the elements present in the star. These lines can also help determine the redshift or blueshift of the star. However, it is important to look at the entire pattern of the spectrum to accurately identify the elements and determine the redshift. Clues from the intensity distribution of the spectrum can also provide useful information even without clear absorption lines. It is easier to determine the redshift with more detailed information.
Phys12
As far as I know, when we use the spectrum of a star, we see where the absorption lines are and using this, we can detect the elements that are present in the star. We also measure whether those absorption lines are supposed to be for a particular element. But why is it not possible that the star contains a different element altogether because the absorption lines are in a different place instead of the spectrum being redshifted/blueshifted?

Thanks!

The relative strengths and the relative spacing of spectral features provide a lot of information which can be used to help identify them. You can match the patterns with other known stars to work out the redshift.

Jonathan Scott said:
The relative strengths and the relative spacing of spectral features provide a lot of information which can be used to help identify them. You can match the patterns with other known stars to work out the redshift.
Oh, so it's because we look at the entire pattern, got it. So, if it were the case, that we looked at just one absorption line (because that's all that we'd have), then we couldn't determine the redshift/blueshift, right?

Phys12 said:
Oh, so it's because we look at the entire pattern, got it. So, if it were the case, that we looked at just one absorption line (because that's all that we'd have), then we couldn't determine the redshift/blueshift, right?
We also have clues from the intensity distribution of the spectrum even where there are no clear lines, and if there was only one line it might well be the strongest expected one for that type of object, but certainly the more detail the easier it is to be sure.

Phys12

## 1. What is redshift and why is it important to measure?

Redshift is the phenomenon in which light from distant objects appears to have longer wavelengths, shifting towards the red end of the spectrum. This is due to the expansion of the universe, and is an important tool for scientists to understand the age, size, and composition of galaxies.

## 2. How is redshift measured?

Redshift can be measured by examining the spectrum of light from an object and looking for shifts in the wavelengths of certain spectral lines. By comparing these shifts to known wavelengths, scientists can determine the amount of redshift and calculate the object's distance and velocity.

## 3. What are the different types of redshift?

There are three main types of redshift: cosmological redshift, which is caused by the expansion of the universe; gravitational redshift, which is caused by the gravitational pull of massive objects; and Doppler redshift, which is caused by an object's motion towards or away from an observer.

## 4. How can redshift be used to study the evolution of the universe?

By measuring the redshift of distant objects, scientists can determine their distance and velocity, and therefore their age and size. This information can be used to study the expansion rate of the universe and how it has changed over time, providing insight into the evolution of the universe.

## 5. Are there any challenges in measuring redshift?

One challenge in measuring redshift is the presence of dust and gas in the universe, which can absorb or scatter light, making it more difficult to accurately measure the spectral lines. Additionally, the accuracy of redshift measurements can be affected by the quality and resolution of the instruments used to observe the light from distant objects.

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