VIII.   GALACTIC ORBIT


                   

Artist's impression of our Galaxy Milky Way:
Approximate orbit of the Sun (yellow circle) around the Galactic Centre
NASA/JPL-Caltech/ESO/ R. Hurt (Public Domain)

It is only necessary to step from the sunshine to the shade or from summer to winter to understand that the sun is the ultimate source of all energy on our planet. The sun and its planets were formed around the same time. Together they orbit a super-dense "black hole" 26,000 light-years away at the centre of our galaxy. The little entourage travels at 143 miles a second on this journey, (called a galactic year, or cosmic year); but it still takes 230 million years to complete one orbit. The sun has made only 20 orbits since its formation; it is expected to make about 25 more in its current stable form.

The galaxy itself is also moving through the universe at the same time.

There are large masses and gravitational forces along the way, and some astronomers suggest that the sun may "rise and dip" as it travels in its orbital plane, instead of following a "level" path.

Space, though mostly empty, seems widely (albeit thinly) permeated with collections of dust and electronic particles. Some of the dust remains from the original clouds of matter that created the stars; some is created by the sun's and other stars' activity and emissions; some is left behind by larger meteors and comets. Clouds of dust and micrometeorites can potentially cause variations in the amount of energy reaching the earth.

The sun's own internal processes also vary its output slightly, in observable cycles.