|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.