An interferometer measured the change in radius of one...

An interferometer measured the change in radius of one Cepheid as about $10 \%$ during its 10 -day period. The star was measured to have an average radius of 40 million $\mathrm{km} .$ How fast was the surface of the star moving outward, on average, if it took 5 days to expand by $10 \%$ ?

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Key Concepts

Cepheid Variables

Cepheid variables are pulsating stars whose brightness varies in a regular cycle due to periodic changes in their size. Their well-defined period?luminosity relationship makes them valuable for measuring cosmic distances and studying stellar behavior.

Interferometry

Interferometry is an observational technique that combines light from multiple telescopes to achieve high resolution, enabling astronomers to measure fine details in astronomical objects such as changes in the radius of a star over time.

Stellar Pulsation

Stellar pulsation refers to the cyclic expansion and contraction of a star's outer layers, which can lead to measurable changes in its radius and brightness. Understanding these pulsations helps in characterizing the internal processes of stars.

Average Radial Velocity Calculation

This concept involves determining the speed at which a star's surface moves by dividing the change in its radius by the time interval over which the change occurs. It is a basic method for quantifying the dynamics of stellar expansion.

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