Even to the unaided eye, the sky displays a richness of sights. Stars of different brightnesses and colors spangle the blackness of night. Here and there are pairs and clusters. If the right time of year, a band of white encircles the heavens, the Milky Way, bejewelled with bright stars and stamped with mysterious voids. Binoculars and small telescopes reveal more: the Milky Way is made of countless faint stars, while double stars, clusters, and clouds of swirling gas abound.
Powerful telescopes that span the spectrum of radiation, both on the ground and flying above the EarthΓÇÖs atmosphere, have broken open much of the mystery of the starry sky, while at the same time enhancing its beauty. We know the Milky Way is the manifestation of our disk-shaped Galaxy of some 200 billion stars, and that its dark clouds are the starsΓÇÖ hidden birthplaces. From there we can trace the flow of their lives to their deaths as burnt cinders or in powerful explosions that leave behind some of the most bizarre characters to be found anywhere.
Over the past century, our vision has taken us far beyond the home Galaxy into the vastness of the Universe, where we find we are hardly alone. As far as we can see are countless other galaxies of all shapes and sizes set within an ever-expanding space that was created in a ΓÇ£Big BangΓÇ¥ nearly 14 billion years ago.
Along with solutions to old puzzles, however, come new riddles, as most of our Universe appears to be in the form of some kind of unseen ΓÇ£dark matterΓÇ¥ and incomprehensible ΓÇ£dark energyΓÇ¥ whose natures and origins remain unfathomable. Yet with all our questionsΓÇöand knowing that there are questions still to be askedΓÇöwe have learned the most important lesson: that all of this Universe is our home, that it took all of it to make us, that it is ours to behold and enjoy.
Come then on a voyage that begins with our very own star, the Sun. Along the way we will visit the births, lives, and deaths of stars, explore their circling planets, their groups and galaxies, and all the stuff in the spaces between them. We finally launch ourselves deep into the cosmos to witness the birth of it all, and in returning ride the light waves from the dawn of time right back to Earth.
While this course stands on its own, it is also an ideal complement to the first course of the set (Astronomy: Earth, Sky, and Planets http://www.mininova.org/tor/1878193 ), which covers celestial motions, constellations, telescopes, and planetary astronomy, all of it then integrated into a full picture of space and time.