Understanding Our Universe

Our Universe

• Students will be able to explore and understand the terms star, galaxy, Milky Way, and black holes after studying this chapter.

Galaxies

• The word galaxy comes from the Greek word "gala" meaning "milk".
• Our galaxy, the Milky Way, looks like a milky cloud in the night sky and is a spiral type galaxy.
• It has mostly old stars at its center, surrounded by a halo of newly generated stars.
• The Milky Way has more than a billion stars and circles the whole sky.
• Our Sun and its solar system are situated in one of its spiral arms.
• The stars we see at night are part of the Milky Way Galaxy.
• There is still enough gas and other matter in its arms for many more generations of stars.

Milky Way Galaxy

• The Milky Way is approximately 13.6 billion years old.
• It has a diameter of 106,000 light years.
• The center of the galaxy is 10,000-15,000 light years thick.
• It moves at a speed of 2,100,000 kilometers per hour in space.
• It completes one cycle in 225,000,000 years.
• The Sun is approximately 21,000 light years from the center of the galaxy.

Astronomers

• Astronomers collect information about astronomical objects using radio telescopes.
• Astronomy is a very old science that has evolved from studying objects seen in the night sky to studying the whole universe.

Stars and Distance

• Stars are large distances apart, and a light year is the unit of distance used to measure their distances.
• A light year is the distance light travels in one year, which is approximately 9.5 trillion kilometers.

Andromeda Galaxy

• Andromeda is our neighboring galaxy, visible to the naked eye on a clear night.
• It is bigger than the Milky Way and situated about 2.5 million light years away from us.

Types of Galaxies

• There are several types of galaxies, including spiral, elliptical, jellyfish, and irregular galaxies.
• Spiral galaxies have a flat disk-like shape with a bulge in the middle and rotate about their center.
• Elliptical galaxies are oval-shaped, contain mostly old stars, and do not rotate around their centers.
• Jellyfish galaxies have giant tails of young stars extended away from the galaxy disk.
• Irregular galaxies do not have a distinct regular shape.