The Milky Way
Galaxies
Galaxies are large groups of billions of stars. They all rotate slowly around a common center. Galaxies come in all shapes and sizes, as well as colors. Our own galaxy is a typical "Spiral" galaxy we call "The Milky Way".
Our Milky Way
Everything that we can see in modern astronomy, except other galaxies, is all within the Milky Way. So there are a variety of things visible for your viewing enjoyment. Here is a listing of items with brief explanations about each.
Nebula
Nebula is the Latin word for "cloud". In all sense of the word, Nebulas are in fact clouds of gas and dust. The types of gasses, and how they are illuminated produces their fantastic colors. There are 5 main classifications of Nebula.
Planetary Nebula
Called Planetary Nebula because of their resemblance to planets when viewed through the telescope, these nebulas are formed from dying stars that are "puffing" their outer layers off in their last moments of life, a process known as a Nova.
Emission Nebula
Emission Nebula shine brightly due to fluorescence from very hot nearby stars. Formed by the same process that creates Planetary Nebula, only the stars final death throws were more violent.
Reflection Nebula
Reflection Nebula are illuminated by the light of nearby stars. The dust scatters the blue light more than others, so these Nebula often appear more blue than the stars that are illuminating it.
Dark Nebula
Dark nebula (also called Absorption Nebula) are clouds of thicker or more dense gases and dust that actually blocks the light of stars behind them. We see them not by looking directly at them, but rather by seeing them silhouetted upon a brighter background.
Supernova Remnant
This is the most violent end to a stars life, short of becoming a Black Hole. These are created when a massive star finally collapses and explodes.
Star Clusters
Star clusters are groups of stars associated with each other. These groupings can be spectacular groups of hundreds of thousands of stars, down to mere handfuls. There are 2 common types of star clusters.
Open Clusters
Also called galactic clusters since they are found within the galaxy, open clusters are loose groupings of stars. Some are more compact like the Pleiades (shown), while others are much looser and hard to distinguish from the surrounding random stars. Open clusters are stars that formed from the debris of older stars well after the formation of the Milky Way. Open clusters contain relatively new stars, and usually appear bluish, and have a surrounding nebula where more stars are being formed.
Globular Clusters
Globular clusters are named so due to their apparent spherical shapes. These groupings appear only as fuzzy points of light to the naked eye, but with large telescopes, show many thousands, or even millions of stars. These stars often rotate around a common center within the cluster. Globular clusters contain the oldest stars in the Milky Way because they were formed early on, when the galaxy itself was still forming. Since globular clusters are so old, the stars within are usually Red Giants. These are stars that are near the end of their lifespan. Globular clusters are not actually within the galaxy, but rather surround the galaxy in an area known as the "Halo".
Stars, Stars, and more Stars
In the simplest of terms, stars are huge balls of burning gas. Nuclear fusion within the star is converting hydrogen into helium. Over the course of the stars evolution, it uses up its supply of hydrogen, and begins this process on heavier elements. The size and color of stars tell us at what stage of life a star is in. The color of the star determines the stars temperature. There are 7 classifications of this "Spectral" type. Our Sun is a type "G" (yellow-white) star burning at around 5,000 - 6,000 degrees Kelvin. There are also 9 classes of star sizes from a White Dwarf, to a Super-giant. The Sun is what's called a "Main Sequence", or type V (Roman numeral 5) star. This is to say it is in the Main stage of its life, or an adult star.
Multiple Stars
Multiple stars are those that have at least one companion star. Many of these are interesting objects to view in telescopes, especially when you can resolve (see both companions) the stars and each are a different color. There are 2 main types of multiple star systems. The first are true physical multiple or binary stars. These are stars that are gravitationally bound to orbit one another. The other type are optical multiple or binary stars. These stars seem to be close to each other because they appear along the same line of sight from our perspective, but are in fact unrelated, and very far apart. With true multiples, there are instances where one star will pass in front of the other from our view. These are called "Eclipsing Binaries". When this happens, the star's light will brighten and darken as the eclipsing star passes its companion.
Pulsating Variables
Pulsating variables are usually giant, or super-giant stars that periodically expand and contract, thereby varying in temperature and magnitude (brightness). This is the beginning of the end for a star's life. As the star uses up the last of its fuel, it begins to expand and goes through bursts of energy, then contracts under its gravity and dimming again. The cycle for this can vary depending on the type of pulsating variable, and the type of star.
Eruptive Variables
These types of variables are stars that experience explosions, ranging from mild to catastrophic. A Nova occurs in close binary systems where the gasses from one star feed a white dwarf companion until it ignites, causing the star to brighten up to 16 times. Novas are not "self-destructive", but rather dim over time and begin the cycle over and over again. A Supernova is when a very massive, unstable star explodes, largely destroying itself. This process happens suddenly over the course of one day, brightening the star 20 times, and slowly fading over the course of a few months, or even years. The remaining "core" of this star collapses under its gravity to the size of a large city and spins very rapidly. The resulting star is then called a "Pulsar". If the beginning star was massive enough, its core could continue collapsing upon itself, and become a "Black Hole", where the gravitational pull of the star is so great, that light can not even escape it.
Rotating Variables
Rotating variables are stars that brighten and darken over time due to dark patches, or sunspots, that develop and disappear periodically. Our Sun is of this type with an 11-year sunspot cycle.