Introduction and Overview
An Introduction to the Night Sky
When we look up at a dark and clear night sky, we see only objects bright enough for the human eye to detect. The technology of telescopes and photography enhance our vision, magnifying our view of the heavens and giving them greater definition. Hundreds of years of research in astronomy and astrophysics have deepened our understanding, adding colour and meaning to the bright speckles and smudges that spangle the darkness above.
With only our eyes, we can see a scant few bright planets shifting against a background of myriad stars. Venus and Mercury orbit close to the Sun, and often make themselves brilliantly obvious at dawn or dusk. Earth's Moon dances through the sky with one face constantly gazing at us in a tidal lock. Mars, surrounded by the modern mythology of science fiction, appears in the sky as a haunting red star. At its closest, Jupiter dominates the sky with a golden luminescence. Saturn, further than Jupiter, is less apparent, but still brighter than most stars.
Saturn, imaged by HCO member Bob Sayer through his own telescope.
The turbulent cloud bands of Jupiter and the elegant rings of Saturn are revealed through even a modest telescope. With larger telescopes we may pick out the distant discs of Uranus and Neptune and bury our eyes into the deep sky. In our own galaxy, we see nebulae - dusty nurseries of newborn stars and the dying embers of supernovae. Beyond the Milky Way, we see billions of galaxies, some smaller versions of our own and some incomprehensibly huge and far away, which power great jets and beams that shine across the expanse of space.
Our own galaxy, the Milky Way, is host to hundreds of billions of stars which form a disk 100,000 light years across. The stars we see above us are only those in the local vicinity, within a few thousand light years. The light from those beyond is dimmed by the very dust from which they are born. The stars we can see are very diverse and even with unaided eyes we can perceive slight differences in colour between them. For example, the star Vega is blue-white, Betelgeuse, the shoulder of Orion, is red and Capella is yellow. These stars are some of the brightest in the sky, but they are all at different stages in their lives and vary considerably in size and distance.
The constellation of Orion, with some of the brightest stars labelled. This is only a simulation, but it illustrates the different colours of the stars. Screenshot from Stellarium.
Our Sun and solar system are embedded in the Galactic disk, about half-way from the centre. From a dark-sky site, unpolluted by artificial light, we see where the Milky Way got its name. A pale river of light spans the whole sky. Were we to be floating freely in space, our view unobstructed by the Earth below us, we would see a full ring formed around us.
Staring out into the magnificent mural of night and knowing a little about the lights that hang there, gazing out between the planets and past the stars, across the Galactic disk and into the infinite beyond, we find some sense of where we stand. While we approach insignificance in the grand cosmic scale, we are privileged in our capacity to reason and understand.