# Spectra Y-axis

1. Nov 1, 2008

### Lorna

Hi everyone,

What does the "relative intensity" mean when we talk about spectra? The intensity relative to what, the background?

Thank you

2. Nov 2, 2008

### astrorob

Different designs of spectrograph will record different intensities for the same wavelength band for the same source - this is due to the sensitivities of each instrument (through CCD efficiency etc..) and also the quality of observation time (spectroscopic, twilight, night etc..) unless you're using an integral field unit, in which case all the light is detected anyway..

Regardless, relative intensity is just a term used to describe the intensity of light detected in a given wavelength band for that specific instrument.

3. Nov 3, 2008

### Lorna

so is it the same as the specific intensitiy? the Intensity per unit frequency or wavelength?