An artist's illustration of an Earth-like planet. The search for planets that are similar to Earth is one of NASA's main goals. Many planets have already been discovered orbiting other stars, but so far only larger planets (the size of Jupiter or larger) have been found. New missions are being planned by NASA which will be able to detect smaller Earth-sized planets. Some of these missions will also try to detect signs of life on these planets by studying emissions in their atmospheres.


Our Milky Way Galaxy

This is our home galaxy called "Milky Way" This arrow shows us where our sun is in the galaxy.

The Milky Way is a galaxy that contains at least 200 billion stars and their planetary systems. It is an average-size galaxy of the barred spiral class. This means that there is a central bulge, with arms, which extend for several light-years*. However, the term "barred" means that its central bulge is elongated; in the Milky Way, this elongation is at a ratio of 2:3, meaning that it is about one and a half times as long as it is wide.
The Milky Way has five distinct arms protruding from the central bulge. Their names are as follows: the Cygnus Arm, Centarus Arm, Sagittarius Arm, Orion Arm, and Perseus Arm. Our solar system lies in the Orion Arm.
The Milky Way belongs to a group of galaxies that is known as the Local Group. The Local Group contains about 30 galaxies, two of which are the Andromeda Galaxy and the Triangulum Galaxy. The Local Group is 9 million light-years in diameter.
In turn, the Local Group belongs to a much larger group of galaxies which known as the Virgo Supercluster. The Milky Way lies on the outer edge of the supercluster. The Virgo Supercluster is about 100 million light-years in diameter.
The Milky Way is 100 thousand light-years in diameter. The Milky Way takes approximately 225 million years to rotate, clockwise, even though the arm that we are in is whipping around the center at about 465,000 miles an hour. At that speed, a space ship from Earth would only need a half an hour to get to the moon!

This image is of the night sky the Milky Way Galaxy.
When we look up at the night sky we can see part of the Milky Way galaxy stretching across the night sky even though we are part of the Milky Way. That is because we are located at one small part of the Milky Way Galaxy and from our position we can see the dense cloud of stars formin another piece of the Milky Way.

  Properties of the Milky Way
Diameter of the Galaxy 100,000 light years
Classification of the Galaxy SBbc
Number of stars in the Galaxy 200 billion
Mass of the Galaxy 1 trillion solar masses
Length of the central bar 25,000 light years
Distance of the Sun from the centre 26,000 light years
Thickness of the Galaxy at the Sun 2,000 light years
Velocity of Sun around the Galaxy 220 km/s
Orbital period of Sun around the Galaxy 225 million years

Below - four galaxies which look like the Milky Way. NGC 3953 (top left) is 55 million light years away and 95,000 light years in diameter. NGC 5970 (top right) is 105 million light years away and 85,000 light years in diameter. NGC 7329 (bottom left) is even further at a distance of 140 million light years but it is larger with a diameter of 140,000 light years. NGC 7723 (bottom right) is 80 million light years away with a diameter of 90,000 light years.

 How many galaxies are in the Universe?
The known universe consists of about 200 to 300 billion galaxies.
Visit this great site "We Are Not Alone" for more information about stars and galaxies.

How the Milky Way Worksclick here, here & here.
The Stars of the Milky Way
Galactic Habitable Zone

What is a light year?
*One light year is about 5,878,499,000,000 miles.

New Tourist's Guide to the Milky Way
The picture of our galaxy is constantly changing as technology improves.

Travel 10 million light years.....In 1 minutes. (Video)
Travel through your universe from outside the milky way down into the atoms which make up your world.

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