For the majority of galaxies astronomers observe, the light...

Name: Problem 3, Chapter 75: Pathways to Astronomy
Uploaded: 2020-10-14T21:58:59-08:00
Duration: 1 min 56 s
Channel: Farhanul Hasan
Description: For the majority of galaxies astronomers observe, the light travel time is less than a billion years. This is only a fraction of the Sun's age, and therefore we do not expect to find many differences in the galaxies' properties due to their age. What would the redshift be for a galaxy that we are seeing as it was billion years ago?

For the majority of galaxies astronomers observe, the light travel time is less than a billion years. This is only a fraction of the Sun's age, and therefore we do not expect to find many differences in the galaxies' properties due to their age. What would the redshift be for a galaxy that we are seeing as it was billion years ago?

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Key Concepts

Redshift

Redshift is a measure of how much the wavelength of light from an astronomical object has been stretched due to the expansion of the universe. In cosmology, it provides a way to determine how fast an object is receding from us and gives a clue about its distance and the time at which its light was emitted.

Lookback Time

Lookback time refers to the time elapsed between the emission of light from a distant galaxy and its detection on Earth. It allows astronomers to view the galaxy as it was in the past, effectively turning telescopes into time machines that reveal the history of the universe.

Cosmological Expansion

Cosmological expansion describes the process by which the universe is increasing in size over time. This expansion stretches the wavelengths of light from distant objects, leading to redshift, and is a fundamental aspect of modern cosmology that connects redshift measurements with the age and evolution of the universe.

Redshift-Lookback Time Relation

The relation between redshift and lookback time comes from the dynamic expansion history of the universe. A light travel time of about one billion years typically corresponds to a relatively small redshift (on the order of 0.07 to 0.1), implying that the galaxy is seen as it was only slightly earlier in cosmic time compared to our current epoch.

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