Our Solar System's Location in the Milky Way Galaxy (은하계에서의 태양계의 위치) 

[정승남세기영어교육연구회장]

Our Solar System's Location in the Milky Way Galaxy

(은하계에서의 태양계의 위치)

A galaxy is a huge group of stars, dust, gas, and other celestial bodies bound together by gravitational forces. There are spiral, elliptical, and irregularly shaped galaxies. Galaxies contain anywhere from 100,000 to 3,000,000,000,000 stars.

There are three major types of galaxies: spiral (with arms), elliptical (no arm), and irregular (without rotational symmetry). Galaxies radiate a continuous spectrum of energy. Some radiate radio waves, X rays, and infrared, and ultraviolet (UV) radiation.

The Earth, Sun and the rest of our solar system are a tiny part of the Milky Way Galaxy, a spiral galaxy.

The Milky way Galaxy is just one galaxy in a group of galaxies called the Local Group. Within the Local Group, the Milky Way Galaxy is moving about 300 km/sec (towards the constellation Virgo).

The galaxy that is nearest to our galaxy is the Sagittarius Dwarf galaxy, which is about 24 kiloparsecs or 80,000 light years from us. The Large Magellanic Cloud is another close galaxy; it is about 50 kiloparsecs from us.

From the Earth, our Milky Way Galaxy is visible as a milky band that stretches across the night sky. It is easier to see when you are far from bright city lights.

Our solar system is located in the outer reaches of the Milky Way Galaxy, which is a spiral galaxy. The Milky Way Galaxy contains roughly 200 billion stars. Most of these stars are not visible from Earth. Almost everything that we can see in the sky belongs to the Milky Way Galaxy.

The sun is about 26,000 light-years from the center of the Milky Way Galaxy, which is about 80,000 to 120,000 light-years across (and less than 7,000 light-years thick). We are located on one of its spiral arms, out towards the edge. It takes the sun (and our solar system) roughly 200-250 million years to orbit once around the Milky Way. In this orbit, we (and the rest of the Solar System) are traveling at a velocity of about 155 miles/sec (250 km/sec).

To reach the center of the Milky Way Galaxy starting from the Earth, aim toward the constellation Sagittarius. If you were in a spacecraft, during the trip you would pass the stars in Sagittarius one by one (and many other stars!).

Since we're inside the Milky Way Galaxy and we've never sent a spacecraft outside our Galaxy, we have no photographs of the Milky Way Galaxy. Radio telescope data does, however, let us know a lot about it.

The arms of the Milky Way are named for the constellations that are seen in those directions. The major arms of the Milky Way galaxy are the Perseus Arm, Sagittarius Arm, Centaurus Arm, and Cygnus Arm; our Solar System is in a minor arm called the Orion Spur. The central hub (or central bulge) contains old stars and at least one black hole; younger stars are in the arms, along with dust and gas that form new stars.

The great rift is a series of dark, obscuring dust clouds in the Milky Way. These clouds stretch from the constellation Sagittarius to the constellation Cygnus.

The Milky way Galaxy is just one galaxy in a group of galaxies called the Local Group. Within the Local Group, the Milky Way Galaxy is moving about 300 km/sec (towards the constellation Virgo). The Milky Way Galaxy is moving in concert with the other galaxies in the Local Group (the Local Group is defined as those nearby galaxies that are moving in concert with each other, independent of the "Hubble flow" expansion).

Harlow Shapley (November 2, 1885- October 20, 1972), an American astronomer, was the first person to estimate the size of the Milky Way Galaxy, as well as our position in the galaxy (about 1918).

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