... As an experiment, I made some three-color images of Messier 42, more commonly known as the Great Nebula of Orion. ... green enhanced . ... halfsize or fullsize . ... Each image is a ``true color'' composite of three monochromatic images, in which the red, green, and blue intensities each correspond to the intensity of one of the original images. ... The HST image is assembled from different filters than mine: red is Nitrogen [II] at 6583 , green is H-alpha at 6563 , and blue is O [III] at 5007 . ...

... 2.3 Data acquisition Spectra generated by the Multibeam correlator contain the usual structure seen in spectra from other H i instruments: a bandpass spectrum which is the sum of the sky , ground and receiver temperatures multiplied by the product of the filters in the receiver chain; superimposed on this is a noise ... Note also that sources extended much beyond ,40 arcmin can be imaged poorly in HIPASS images because of the bandpass sidelobe effect described in Section 3.3. ...