When you look at the night sky and make a wish upon your favorite star, you may not be wishing on a star at all. What most of us perceive with our eyes to be stars are sometimes much much more.
Some of the objects in the night sky are actually just the planets in our solar system reflecting the sun’s bright sunlight. Other objects may be comets or a whole galaxy of stars. Though these objects seem close together in the sky, we know that they are actually a great great distance apart.
To get a better picture of the immense size of the universe we study many of the objects in space and the distances between them.
The best place to start is within our solar system.
Galaxies are made up of nebulae, dust billions of stars, and all of the objects that are orbiting those stars.
There are three main types of galaxies: irregular, spiral, and elliptical. Irregular galaxies have odd differing shapes and are hard to classify. Spiral galaxies, however, can be broken down into categories. In some spirals the “arms” spread from a center that looks circular and others have “arms” that appear to dangle as if from the ends of a block or bar. The ones with circular centers are just called spirals while the ones with bar centers are called barred spirals.
The Universe
The Universe is made up of millions of galaxies. Also out in space is background radiation from all the explosions and nuclear fusion going on within stars and nebulae. And, of course, the universe has a whole lot of empty space.
In fact, there is so much space even between single stars in a galaxy that it is difficult to measure in miles or kilometers. Scientists use a distance measurement in space that is expressed as the distance light will travel in the course of a year – a light year. Light travels at a speed of about 186,000 miles per second. That means that light can travel 7.5 times around the entire world in just 1 second! In a year’s time, light can travel six trillion miles (6,000,000,000,000). It takes over 4 years for the light from the nearest star to reach the Earth.
