Galaxies

A galaxy is a system of many thousands of millions of stars, together with interstellar gas and dust. Galaxies may be spiral, spherical, elliptical or irregular  in shape. Telescopes have revealed the existence of about 1000 million galaxies, although only very few of those can be seen with the naked eye.

The system for classifying galaxies was designed by the American astronomer Edwin Hubble and is still used today, despite it's artificial attributes.  Galaxies are grouped into three basic categories: elliptical, spiral and irregular.
 

• Elliptical galaxies range from the spherical EO type to the very flattened E7.
• Spiral galaxies include our own Milky Way galaxy, and the well known giant galaxy of Andromeda.  They are classified Sa, Sb or Sc, depending upon how tightly wound the arms are. The so-called barred spirals galaxies have arms coming from the ends of a central bar and these are designated SBa, SBb or SBc.
• Irregular galaxies includes all those whose shape is neither spiral nor elliptical, for example teh large and small magallenic clouds.

The Milky Way Galaxy

Our own galaxy - still known by it's ancient title the Milky Way - is a fairly ordinary spiral galaxy.  Nevertheless it is unimaginatively huge; about 100 000 light years in diameter and containing some ten billion (10,000,000,000) stars.  Our Sun is situated in one of the spiral arms, about 30,000 light years from the galactic centre.  The Milky Way Galaxy is rotating and the Sun takes 225 million years to complete one revolution. This is sometimes called a cosmic year.
 
 
 
 

Universe

 
 
 
 

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