This insignificant patch of sky in the fairly obscure constellation of Fornax is the setting for one of the most remarkable images ever captured. Although only a fraction of the full moon in size, this image traces thousands of distant galaxies to the edge of the observable universe.
The Hubble Space Telescope began observing “deep fields” in 1995. The idea was not new – astronomers have always tried to take longer photographic captures that draw in more light to reveal ever more faint and distant objects. Observing more distant galaxies sheds light on how they form, and how their shapes and sizes change over time. Hubble’s key advantage is that, floating in orbit, it’s unaffected by the blurring effect of the atmosphere and so can provide images of far superior resolution than ground-based telescopes.
Careful planning was required for the deep field images. An “empty” piece of sky was needed that contained no bright sources of visible light that might drown out fainter objects. There could also be no bright sources at other wavelengths, such as X-ray or radio waves where complementary supporting observations might be made. The direction chosen was away from the millions of faint stars and dust of the plane of our own galaxy, the Milky Way.
This was not without risk, however. Hubble was, and still is, a hugely popular, world-class research facility. It is typical that demand for Hubble’s instruments outstrips availability by six or seven times. There was always the possibility that the 10 days observation required might reveal the carefully-chosen blank part of the sky to be just that: blank.
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