Hubble Deep Field South - Planning

Planning

The rationale behind making another Deep Field image was to provide observatories in the southern hemisphere with a similarly deep optical image of the distant universe as had been provided to those in the northern hemisphere.

The field chosen was in the constellation of Tucana at a right ascension of 22h 32m 56.22s and declination of -60° 33′ 02.69″. As with the original Hubble Deep Field (referred to hereafter as the 'HDF-N'), the target area was selected to be far from the plane of the Milky Way's galactic disk, which contains a large amount of obscuring matter, and to contain as few galactic stars as possible. However the field is closer to the galactic plane than the HDF-N, meaning that it contains more galactic stars. It also has a nearby bright star, as well as a moderately strong radio source close by, but in both cases it was decided that these wouldn't compromise follow-up observations.

As with the HDF-N, the field lies in Hubble's Continuous Viewing Zone (CVZ), this time in the south, allowing twice the normal observing time per orbit. At specific times of year, the HST can observe this zone continuously, without it being eclipsed by the Earth. Viewing this field, however, has some issues due to passages through the South Atlantic Anomaly and also with scattered earthshine during daylight hours; the latter can be avoided by using instruments with larger sources of noise, for example from the CCD reading process, at those times. The survey again used Director's Discretionary Time.

The field was imaged briefly on October 30–31, 1997 to make sure that the guide stars in the field were acceptable; these guide stars would be required to keep the HST accurately pointing on the region during the observations proper.