Astronomy Answers: From the Astronomical Dictionary

Astronomy Answers
From the Astronomical Dictionary

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The description of the word you requested from the astronomical dictionary is given below.

the filter

filtrum = [Middle Latin] compacted wool; from feltir = [German] felt

A filter is a device that transmits only certain (ranges of) colors (or frequencies) from the electromagnetic spectrum. A broadband filter transmits a wide range of frequencies, and a narrowband filter only a small range. With a narrowband filter, spectral lines can be measured.