STUDY OF THE UNIVERSE

A UNIVERSAL VIEW

Earth was once thought to be the center of the universe.We know that Earth and its neighboring planets are merely tiny speck of agglomerated debris left behind from formation of the Sun 5billion years ago. Except for being our parent star, the sun is relatively unremarkable star. It lies in the hinterlands of the Milky Way galaxy, a vast, pancake-shaped city of 300 billion stars. Like islands scattered across an archipelago, many billions of other galaxies lie beyond the Milky Way, out to the horizon of the visible universe. On the largest scale, the structure in the universe resembles a great sponge, where long filamentary clusters of galaxies are the fabric in the sponge, and mysterious, as yet unidentified dark voids in space are the "HOLES".   

COSMIC EVOLUTION

Today we know that the universe is active, dynamic, and ever changing. Stars explode; galaxies collide; black hole devour matter. The very fabric of space and time was apparently forged in an incredible explosion, called The Big Bang, some 15 billion years ago.

Our past and destiny are intertwined with the violent cosmic events that shaped the cosmos. many of the atoms in our bodies - Calcium, Nitrogen, and Iron, for instance - were forged in the hearts of ancient stars that exploded long ago, spewing material back into space. Other cosmic catastrophes - an Asteroid's collision with Earth, radiation from a nearby supernova, or changes in the Sun's brightness - may have affected the evolution of life in the past and may do so again in the future.

THE ASTRONOMICAL ZOO

PLANETS - Our solar system consists of nine known planets, several dozen moons, thousands of rocky and metallic asteroids, and trillions of icy bodies called comets. All of these objects are gravitationally bound to the Sun. The solar system has two types of planets: the tiny rocky planets of Mercury, Venus, Earth, and Mars, which all lie close to the Sun; and the immense liquid and gaseous outer planets of Jupiter, Saturn, Uranus, Neptune, which lie in the colder reaches of the solar system. The farthest planet from the Sun, icy Pluto, may actually be a "double planet", because it orbited by moon nearly one-quarter its size. Thousands of icy dwarf bodies similar to Pluto may have inhabited the early solar system.


STARS - Stars are massive, self-luminous objects that from the basic building blocks of the cosmos. They coalesce under gravity to form great clusters and galaxies. Stars are also fundamental engines that generate energy by smashing lighter elements together to form a heavier elements through a process called nuclear fusion. Our Sun is the closest star to Earth, and very typical of stars in general. Every second, the Sun converts 540 million tons of hydrogen into 595 million tons of helium. In the process, 49 million tons of matter is converted to pure energy, which eventually reaches Earth as "LIGHT". 


The basic recipe for making a star is fairly simple: compress a huge cloud of interstellar dust and gas into a relatively small, dense globule of hydrogen. Then Collapse this cloud, perhaps with a shock wave from a nearby stellar explosion. The cloud continue to collapse under gravity until nuclear fusion begins, its outward force counterbalancing any further collapse. When this equilibrium is reached, a STAR is born. Even a casual glance into evening sky reveals that stars come in a wide range of brightness and colors. Some stars appear bright because they are close neighbors to the Sun. Others are intrinsically bright because they are much hotter that the Sun. Stars colors also provide clues to their intrinsic nature. Bluish-colored are hotter than the Sun; Reddish are Cooler. Extremely hot star can be 10 or even 100 times more massive than our Sun.


Galaxies - Our Milky Way was once thought to contain all stars in the universe. In the 1920's however, American astronomer Edwin Hubble discovered that the universe is filled with other island  cities of stars as well. Hubble classified galaxies according to shape. Many are spiral, or pinwheel-shaped, like our Milky Way. Others are elliptical, and still others are irregular. Today, astronomers are presented with a truly dizzying variety of galaxies-radio galaxies, infrared galaxies, X-ray galaxies, active galaxies - but there is yet no coherent scheme of galactic evolution.  


The core of some galaxies are extraordinarily bright, shining at a level equal to compressing 1 million Suns into a piece of space no larger than our solar system. This active galactic nuclei maybe powered by immense black holes that have grown perhaps from the merger of individual stellar black holes. Star dust and gas swirling down into the hole heat up to millions of degrees, allowing a prodigious amount of energy to be radiated.


Brighter than 1 million supernovas going off in unison, Quasars are probably the most energetic type of active galactic nucleus. Quasars stands for Quasi-Stellar object, because it is brilliant, point like, and virtually indistinguishable from stars in photographic sky surveys. However, Quasars are many billions of light year away, far too distant to be individual stars.