History of the worlds content

There are many obstacles to extragalactic astronomy. The main difficulty is that the very great distances involved imply extremely limited sizes and apparent luminosities. In addition, large distances mean spectral shifts from the interesting spectral region (blue) into the near infrared, which is difficult to detect. 

This world cannot be motionless. It must move if it is not to collapse. The planets revolve around the stars, whilst the stars whirl around the centre of the Galaxy. Galaxies themselves form moving swarms called clusters, and these clusters move away from one another, swept along by the expansion of the Universe. If they did not, they would simply hurl themselves together under the effect of gravity. The Universe is expanding, and it is this that saves it from collapse. Everywhere and on every scale, motions clearly oppose fall. 

Having measured the world s content, the next step is to retrace its past evolution. Time now becomes a parameter. Through the interactions they are involved in, and these depend on the prevailing physical conditions, particles are the driving force for an evolutionary structuring process that implicates time. 

The aim of this intellectual discipline which we call astrophysics is to try to understand the unifying features of the inventory of light and matter, visible and invisible, whose character seems so chaotic and unbounded to discern its physical basis, consistency and wholeness. 

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