The New Sustainability
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The Hubble Deep Field (HDF) is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, about one 24-millionth of the whole sky, which is equivalent in angular size to a 65 mm tennis ball at a distance of 100 meters. The image was assembled from 342 separate exposures taken with the Space Telescope's Wide Field and Planetary Camera 2 over ten consecutive days between December 18 and December 28, 1995.
The field is so small that only a few foreground stars in the Milky Way lie within it; thus, almost all of the 3,000 objects in the image are galaxies, some of which are among the youngest and most distant known.
Over recent millennia, orbital forcing has continually reduced summer insolation in the Northern Hemisphere5. Peak insolation changes in Northern Hemisphere high latitudes, at ~65° N between June–August (JJA), have been identified as the prime forcing of climate variability over the past million years1. Together with long-term CO2 variability resulting from biogeochemical feedbacks of the marine and terrestrial ecosystems14, these insolation cycles have initiated the interplay between glacial and interglacial periods.What is this orbital forcing? What is solar insolation?