For the sake of simplicity – for now – here are the four most common that you can see with the naked eye or a telescope or pair of binoculars:
To set the record straight from the get-go, our Sun is a star. And stars are all objects more-or-less like our sun.
Stars are huge (100s of thousands to millions of km+ in diameter) balls of mostly hydrogen and helium “burning” for hundreds of millions to billions of years via nuclear reactions. (If a star was just a lump of material combusting like a log in a fire, it would only burn for a few million years at most.)
Depending on the temperature at which they burn, stars can be red, orange, yellow, white, or blue (a red star is least hot, a blue star is super-hot) and range in size from dwarfs about the size of Jupiter to hyper-giants the diameter of Saturn’s orbit around our star. (For comparison, our “star” the Sun is a yellow star about 1 million km in diameter.)
While some stars just look like they’re close together because of the line of sight we have on them from Earth, some stars actually are close together, bound by time and gravity into clusters.
Open clusters, such as the Beehive Cluster in the constellation Leo, are just that. Globular clusters, such as the Hercules Cluster seen in the constellation of the same name look like spectacular starbursts, as pictured at right.
Some of these clusters – such as Omega Centauri, visible only in the Southern Hemisphere – contain a million suns, like a sort-of mini galaxy within a galaxy.
While black holes are popularly known as the stage at which really big stars “die”, many nebulas visible in the sky could be seen as cosmic maternity wards, where dust from dead or dying stars collects back together to form new stars.
While some nebulas we see are still in the process of shedding off material from a dying star (such as the Ring Nebula) others (such as the Orion Nebula in the direction of the constellation of the same name) are actively nurturing new white and blue suns into stellar childhood.
When you see the “Milky Way” in a really dark night sky, you’re actually looking at a portion of one of the spiral arms that make up the “pinwheel” of our home galaxy. And you’re looking at that spiral arm from inside a neighbouring spiral arm:
The thousands of stars you see in a dark sky are a small portion of those that reside in the spiral arm we live in. We see the next spiral arm in our galaxy (i.e. the “The Milky Way”) as a cloud that doesn’t totally resolve into individual stars because we’re looking at a portion of the 100-400 billion stars in our home galaxy.
Throughout the universe, there are countless trillions of galaxies, each with billions to hundreds of billions or more stars orbiting around a central nucleus.
Our neighbouring galaxy – Andromeda – is still so far away that if you could travel at the speed of light – 300,000 km/per second (Moon & back in 2 seconds) – it would take 2 million years to get there.