Tuesday, April 8, 2014

G is for Galaxies

Our Milky Way. Home Sweet home.
A Galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust.
Examples of galaxies range from dwarfs with as few as ten million stars to giants with a hundred trillion stars, each orbiting their galaxy’s own center of mass.
The word galaxy comes from the Greek word for "milky".
There are probably more than 170 billion galaxies in the observable universe.
Galaxies are classified into three main types: spiral galaxies, elliptical galaxies, and irregular galaxies.
The most beautiful type of galaxies are Spiral Galaxies. Their long twisting arms are areas where stars are being formed.
The stars found in Elliptical Galaxies are often very old. This is because elliptical galaxies don't actively create new stars. The only stars found within them were created along time ago.
Irregular Galaxies are simply all the galaxies which are not spiral or elliptical. They can look like anything and have many different characteristics.
Some scientists think that most of the mass of a galaxy is made up of a mysterious substance called dark matter.
It takes over two hundred million years for the sun to orbit the center of the galaxy. This is called a galactic year.
Galaxies with less than a billion stars are considered "small galaxies." In our own galaxy, the sun is just one of about 100 billion stars.
The Local Group
There are billions of galaxies in our Universe. Most of these are clumped together in small groups. Our own galaxy which is called The Milky Way Galaxy lies within a group of galaxies that we call The Local Group.
Some galaxies occur alone or in pairs, but they are more often parts of larger associations known as groups, clusters, and superclusters.
Galaxies in such groups often interact and even merge together in a dynamic cosmic dance of interacting gravity. Mergers cause gases to flow towards the galactic center, which can trigger phenomena like rapid star formation.
Our own Milky Way may someday merge with the Andromeda galaxy—just two million light-years away and visible to the naked eye from Earth's Northern Hemisphere.
2014 Celestial Calendar: April 8 - Mars at Opposition. The red planet will be at its closest approach to Earth and its face will be fully illuminated by the Sun. This is the best time to view and photograph Mars. A medium-sized telescope will allow you to see some of the dark details on the planet's orange surface. You may even be able to see one or both of the bright white polar ice caps.