Artefacts

Leaving the realm of cosmology and coming literally down to earth, we may look at the artefacts found on the survey plates, as displayed in Fig. 2. There is no doubt that most artefacts are man-made. Aside from dust, which is unavoidable even in a relatively clean measuring environment, and satellite trails, found abundantly, a large source for artefacts are blended stellar images which no doubt owe their existence to the imperfection of imaging and image analysis techniques - aside from the earth's atmosphere. The number of artefacts increases towards the Milky Way fields, in the vicinity of the Small Magellanic cloud, seen in the lower middle of the total field, as well as in the Large Magellanic Cloud which just touches some fields on the left hand side. Other dense regions such as star clusters and clusters of galaxies are not so obvious. Surprisingly, plate edges appear to be well delineated by artefacts. Because of the general small overlap region of the plates, all scans have been made over somewhat larger regions than covered by useful data, just to be sure not to loose information. Cutting the edges properly is then a software process which lists the plate frames as artefacts.