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The Galaxy and The Milky Way

The Galaxy and The Milky Way

Category : science , 2 years ago

The Galaxy

You’ve probably heard that our Sun is located in the Milky Way galaxy. But what is a galaxy anyway? The simple answer is that a galaxy is a huge collection of stars, dust and gas held together by their mutual galaxy.

They usually contain several million to over a trillion stars and can range in size from a few thousand to several hundred thousand light-years across.  In other words, all the stars in a galaxy are kept together by the gravity of all the other stars (as well as the invisible, mysterious dark matter).

There are hundreds of billions of galaxies in the Universe. Galaxies come in many different sizes, shapes and brightness’s and, like stars, is found alone, in pairs, or in larger groups called clusters. Galaxies are divided into three basic types:

  • Spiral
  • Elliptical
  • Irregular

Spiral: Spiral galaxies get their name from the shape of their disks. In a spiral galaxy, the stars, gas and dust are gathered in spiral arms that spread outward from the galaxy's center.

Spiral galaxies are divided into three main types depending on how tightly wound their spiral arms are: Sa, Sb and Sc.

  • Sa galaxies have very tightly wound arms around a larger central nucleus.
  • Sc galaxies have very loosely wound arms around a smaller nucleus.
  • Sb's are between, having moderately wound arms around an average sized nucleus.

Spiral galaxies have a lot of gas, dust and newly forming stars. Since they have a lot of hot, young stars, they are often among the brightest galaxies in the universe. About 20% of all galaxies are spirals. We live in a spiral galaxy called the Milky Way.

Elliptical:  Elliptical galaxies are shaped like ellipses (stretched circles or egg-like). They are divided into eight types: E0-E7 depending on how elliptical they are.

E0 ellipticals are nearly circular, while E7s are very stretched out. Elliptical galaxies are made up of mostly old stars, and do not have much gas and dust.

There is very little new star formation in these galaxies. Elliptical galaxies also come in many sizes. The largest galaxies we see are ellipticals, but, elliptical galaxies can also be small. About 60% of all galaxies are ellipticals.

Irregular:  Irregular galaxies have no particular shape. They are among the smallest galaxies and are full of gas and dust. Having a lot of gas and dust means that these galaxies have a lot of star formation going on within them.

This can make them very bright. The Large and Small Magellanic Clouds are examples of irregular galaxies. They are two small galaxies which orbit around our own Milky Way Galaxy. About 20% of all galaxies are irregulars.

Stars are collected together into galaxies. Galaxies are collected together into groups of galaxies, and these groups are collected into clusters. The largest structures in the Universe are galaxy superclusters, which contain millions of galaxies and can measure hundreds of millions of light-years across.

The Milky Way

The Milky Way is the Galaxy in which we live. It is a spiral shaped galaxy that contains several hundred billion stars, including our solar system is located. It is about 100,000 light-years across and about 10,000 light-years thick.

If you are at a place which has a very dark night sky, you can sometimes see the Milky Way as a thick band of stars in the sky. We live out in the suburbs of the Milky Way - not near the center, but not near the edge either. 

The Earth orbits the Sun in the Solar System, and the Solar System is embedded within this vast galaxy of stars. It is just one of hundreds of billions of galaxies in the Universe, and ours is called the Milky Way because the disk of the galaxy appears to be spanning the night sky like a hazy band of glowing white light.

Many people are not clear about the difference between our Solar System, our Milky Way Galaxy, and the Universe.  Let’s look at the basics.

The solar system consists of the Sun, and its orbiting Planets (including Earth), along with the numerous Moons, the Asteroids, the Meteors, the Meteorites and the Comets. 

Our Sun is just one star among the hundreds of billions of stars in our Milky Way Galaxy. If we shrink the Sun down to smaller than a grain of sand, we can imagine our Solar System to be small enough to fit onto the palm of your hand.  Pluto would orbit about an inch from the middle of your palm.

The Milky Way is big, but some galaxies, like our Andromeda Galaxy neighbor, are much larger.  The universe is all of the galaxies – billions of them. You are one of the billions of people on our Earth. 

Our Earth orbits the Sun in our Solar System.  Our Sun is one star among the billions in the Milky Way Galaxy.  Our Milky Way Galaxy is one among the billions of galaxies in our Universe. 

You are unique in the Universe!