Introduction

One look at the night sky will reveal that the universe is a very big place. With the sky splattered with small dots of slightly different colors and brightness, some that twinkle and some that do not, it is hard to vividly imagine that each of those dots are billions of miles away and millions of miles in diameter. And what we see is NOT all that is there.

So What is Out There?

Our Universe contains billions of stars arranged in groups called galaxies, patterns called constellations, pairs called star systems, or stars just flying solo. Gases, dust particles (the size of planets), and nebulae also grace space with their spectacular presence.

When we look up at the stars at night, they seem inches apart, however inches is further from the truth. They are light years away. We use light years to measure the distance from star to star. Light travels at a whopping 186,000 mi/sec or 5,869,713,600,000 (pronounced 5 Trillion 869 Billion 713 million 600 hundred thousand) miles per year! Thus the term light year. Even though some of these stars are thousands of light years apart They are also thousands of light years away. So how do astronomers determines a star's size and brightness if they are so far away?

Magnitude

A star's magnitude relates to the star's brightness. Since our sun is the closest star, we compare all other stars' brightness to our sun as a reference. Our sun has a brightness of 1. Any star brighter than the sun will have a brightness greater than 1. Any star dimmer than the sun will have a brightness less than 1. If all of the stars were the same standard distance from Earth, it would be easy to see which stars were brightest compared to other stars. We refer to the magnitude based on a standard distance as absolute magnitude. Since all stars are not the same distance from Earth, we see their apparent magnitude.

Scientists classify stars according to size, temperature, and magnitude or brightness. They use a graph called the Hertzsprung-Russell Diagram to show the relationship between these characteristics. There is an diagonal band on this graph where 90% of all stars are classified. This area is called the main sequence. All main sequence stars fuse hydrogen as their fuel source. The bigger the star, the more hydrogen it fuses. Bigger stars have more magnitude and are are hotter on the main sequence.

Types of Galaxies

Galaxies are really nothing more than giant swarms of stars, dust, gas, and some stuff that scientists call dark matter. There are 3 basic shapes of galaxies: spiral, elliptical, and irregular. And for the sake of middle school science, these 3 shapes are enough. We, here on planet Earth, live in the outer arm of a spiral galaxy called the Milky Way. Scientists believe that there is a relationship between a galaxy's age and shape. Elliptical galaxies are much younger than the spiral ones. Irregular galaxies could be the newer galaxies just beginning their life.

How did we get here?

For years there has been a debate within the scientific community, and WITH the scientific community, about the origin of the Universe. No one claim, at least for this moment, invites everyone to agree. There are two pretty defined beliefs about "the beginning" that draws a line in the sand: The Creation and The Big Bang Theory. Most science texts will adopt the Big Bang Theory with out ever having mentioned The Creation at all. The definitions are listed in the vocabulary box. No matter which origin you side with, it is still important to know both sides. After all, if one wants to debate, one has to know pretty much both sides well!