Students will understand the composition and structure of the universe and Earth's place in it.
The Universe is the total of all space, time, matter, and energy. Earth is a tiny object in the solar system. Scientists are still learning about the universe.
A galaxy is made up of billions of stars and is set apart from other galaxies by an infinite sea of space. The stars occur in groups called galaxies. A galaxy is a large cluster of stars, gas and dust held together by gravity. Galaxies are whirling pools of dust and energy. The distance that light travels in one year is a light year. Galaxies are not close together, they are set apart by large distances, sometimes millions of light years.
The majority of stars in our galaxy are contained in a narrow, globular area, with a wide nucleus or core in the middle. This disk is approximately 100 light years in diameter and the stars in it amass in two circular arms that stretch out from the nucleus. The stars in the circular arms are called Population I stars. Population I stars are all of various ages. Some of them are very young and still in the formation stage; those in the rest of the galaxy are Population II stars and they are all very old. Experts believe that everything in the galaxy was first a globular cloud of gas and dust that slowly settled into the spiral arms, leaving the Population II stars behind. More stars formed from the gas and dust in the spiral arms and the newer stars make up Population I.
Types of Galaxies
There are three main types of galaxies: elliptical, spiral, and irregular. Some are huge, but others are quite small; all are three-dimensional. Spiral galaxies have spiral arms reaching out from the inner hub. Spiral arms are composed of stars and dust. Earth is sits on one of the arms of the galaxy. Galaxies that are neither spiral nor elliptical are irregular galaxies.
The Milky Way
Galaxies amass into clusters. The cluster we live in is the Milky Way. The shape of our galaxy is a rough round disk or sphere. There are many big, round masses of stars linked to our galaxy. These clusters of stars form what appears to be a halo or corona around the central sphere.
The Local Group contains about 25 galaxies of various types and sizes. The Milky Way is a spiral galaxy and it is part of the Local Group. One of the stars in the Milky Way is the sun. The sun is locates about 30,000 light-years from the hub of the galaxy, and like the other stars in the galaxy, it revolves around the core. The sun makes a rotation around the Milky Way every 200 million years. The Milky Way stretches across the sky like a hazy band of light. All of the stars that you can see with your eyes alone are part of the Milky Way. The precise age of the Milky Way is unknown. However, scientists have determined that the oldest star in the galaxy is more than about 13 billion years old!
The Milky Way is our galaxy, but we should not forget that here are billions of other galaxies in the universe, and some may be much like ours. A typical galaxy contains a few million stars. Most other galaxies are either elliptical or spiral-shaped. Other spiral galaxies, like our galaxy, have a nucleus and circular arms. However, elliptical galaxies have no arms.
Quasars were at first believed to be stars, but were later identified as galaxies. Quasars are galaxies that are very far away. They travel very fast, at a speed close to the speed of light. Quasars put out more energy than any other object in the universe. A huge black hole lies at the center of the quasar. This black hole absorbs gas and dust as it speeds through the universe. The energy output comes from the gas and particles of dust as it heats up in the atmosphere.
At the center of every galaxy, including the Milky Way, resides a massive black hole! Black Holes take shape when gigantic stars run out of fuel and collapse, tearing a hole in space. Black Holes emit radiation and gradually vanish.
Pulsars are stars with huge magnetic fields that produce electromagnetic radiation. A pulsar is like a beam that just passes every now and then. They originate from the nucleus of an exploding star. Pulsars revolve at lightning speeds, while they emit radiation. When astronomers first discovered pulsars, scientists believed that their radiation emissions were messages from another world!
The Doppler Effect
The Doppler Effect causes wavelengths of light coming from galaxies to be compressed or stretched out. When a galaxy is moving toward Earth, the wavelengths come together and the light shifts toward the blue-violet end of the spectrum. A galaxy shows a shift towards red when moving away from the Earth. The Doppler Effect is the change in wavelength that occurs in any kind of wave energy. As the energy source, either light or sound, travels toward you, the wavelength becomes shorter, as the energy source travels away from you, the wavelength gets longer.
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