Imagine the Universe!

What is Resolution?

Resolution is the ability to distinguish between two things that are close together. Spatial resolution refers to how far apart two objects have to be on the sky (or as observed by your telescope) before they look like two distinct, separate objects. Spectral or energy resolution is how well a telescope can differentiate between two light signals that are very close in energy or frequency. The higher the resolution, the closer two signals can be while still being recognized as distinct.

Resolution is an important instrument characteristic in astronomy. An imaging telescope with very low spatial resolution will not reveal small features such as a star's nearby companion or the fine structure of a supernova remnant. Instead, they will get blurred together. The effects of spatial resolution can be seen in the images to the right. The first image is a very low resolution one, and is hardly recognizable. The middle image can be seen to be a human face, but it is not clear whose. The bottom image has the maximum resolution for your computer screen, and can be easily seen to be a former President of the U.S.A. (Note: These images probably will not print out if you try to print this page.) With a high resolution instrument, individual features are sharp and crisply defined, and more can be learned about them. A spectrometer's spectral resolution is very important. Without a high spectral resolution, it is impossible to identify the narrow lines of elements and to determine their abundances. Much of the rich information in the spectrum can be lost as features are smeared together.

In the composite spectrum of emission from several supernova remnants below, line emission from elements such as magnesium (Mg) can be isolated. If the spectral resolution were too low, these lines would appear as small humps of increased emission on top of the continuum.

low resolution image of Bill Clinton

medium resolution image of Bill Clinton

high resolution image of Bill Clinton

snr spectra showing lines

Return to the X-ray instrument design page

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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Acting Project Leader: Dr. Barbara Mattson
All material on this site has been created and updated between 1997-2012.

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