FIGURE 3.12 The redshift distance relationship. This diagram shows that galaxies further away are receding from our galaxy at faster rate. The slope of the relationship is given by the Hubble constant (H) measured in kilometers per second per megaparsec. The inverse of the Hubble constant is a simple estimate of the age of the universe. SOURCE: Hubble, 1936.

these efforts created distance scales to accommodate distances beyond the solar system: moving from the solar neighborhood to another spatial context, that of our galaxy, and finally, to a vision of an expanding universe enabled by Edwin Hubble’s work. At this scale, distance becomes time. Thus, spatial thinking brought us not only a picture of the spatial structure of the Universe, but an understanding of its history as well.

As with any complex scientific practice, it is difficult to identify the component operations and impossible to specify a single sequence in which they are performed. Based on the experience of geoscientists, the committee presents a descriptive catalog of the spatial thinking operations typically performed in the process of doing geoscience. It is based on two categories of thinkers: expert geoscientists, especially those undertaking a spatial challenge that is novel to anyone, and beginning students, undertaking a spatial challenge that is novel to them. Thinking spatially by geoscientists and geoscience students involves, among other things,

• describing the shape of an object, rigorously and unambiguously;

• identifying or classifying an object by its shape;

• ascribing meaning to the shape of a natural object;

• recognizing a shape or pattern amid a cluttered or noisy background;