How Can Astronomers Determine the Size of an Emission Region

question 118

Multiple Choice

How can astronomers determine the size of an emission region in a very distant and unresolvable source?

• A) by measuring the object's mass and using a reasonable value for the average density for matter to calculate its volume and hence its diameter
• B) by using radio interferometry because this technique can resolve far greater detail than optical imaging
• C) by measuring brightness variability because an object cannot vary more rapidly than the time taken for light to cross the source
• D) by measuring the redshift of its spectrum because the redshift will depend on the source size

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