What is a galaxy ?
The starry sky has always attracted people's views for its beauty.For centuries it was believed that in addition to the stars on it nothing, and a strange white band called the Milky Way, stretching from horizon to horizon.And this band has created far more theories than any ordinary star.Only in the XVII century, Galileo was able to see that the Milky Way - is not nothing but a giant star cluster.Now we call it the Galaxy.But what a galaxy, the definition of which not everyone knows?
What galaxy by definition?
Galaxy - is a huge system of stars, which has a common center of mass, located generally at its center.This means that all the stars in this system linked their gravity and orbiting around the center.Galaxy device can be compared to our solar system, in which the Sun is the center, and all the planets revolve around it.Only in the galaxy, all distances are much longer, and instead of planets - real stars, sometimes much greater than our sun.Number of stars in one galaxy is huge - hundreds of thousands to trillions.What is a galaxy?In the 5th grade on this issue highlights the natural history lesson.
Galaxies is a lot of different shapes and sizes.All the stars, which are only belong to galaxies.Our Sun, together with all the planets and us, too, is not alone - it belongs to the huge galaxy we call the Milky Way.This Galaxy side like a flattened disk, and we are about halfway between its edge and the center.Therefore, in our sky the Milky Way looks like a white band - we're looking at the galaxy from the inside.The billions of stars that make up her blend into the white band, but the telescope can discern the brightest of them separately.
What are the galaxies?
Scientists love classify all the objects under study.Not spared it a party, and the Galaxy.To date, a so-called Hubble classification, according to which galaxies are divided in appearance and structure to:
Each of these, of course, contains a variety of yet - to fit billions of different galaxies, sometimes it is very unusual for a single classification is not so simple.
Previously, there was another kind of classification - brightest galaxies in the sky.It was called the Harvard classification, the title famous university in the United States.It was there that scientists, using the observation telescope with a mirror diameter of 61 cm, and have developed this classification in 1927.They shared all available for surveillance of the galaxy into 5 classes, according to the letters of the alphabet:
- A - bright galaxies, up to 12 magnitude.
- B - with a brightness of 12 to 14 magnitude.
- C - 14 to 16 magnitude.
- D - 16 to 18 magnitude.
- E - 18 to 20 magnitude.
Now this system is no longer relevant - more sophisticated telescopes can see the galaxy with brightness much smaller magnitude 20.Today, scientists can study even individual stars in some galaxies.
Galaxy - such huge objects that imagination is not able to present all their greatness.But their number in the universe is infinite, and even more - the galaxies themselves constitute a vast "star" system, where each of them - no more than a grain of sand.Such systems are called Metagalaxy.