The Structure of the Universe

1. Hierarchal structure of the universe---

Stars          ®          clusters®            galaxies ®       galactic clusters   ®   universe

2. A star is a huge ball of burning gases that gives off its own light and heat.

a)      Stars begin as a large cloud of gas and dust called a nebula.

b)      Our sun, which is the closest star to Earth, is an average, medium-size star. It is about 1,400,000 km in diameter.

3. A star cluster is a group of stars with similar characteristics that are located near each other.

a)      The similarities among the stars in a cluster suggest that they formed in the same way at around the same time. That is, the stars making up a star cluster are about the same age.

b)      A star cluster may contain between 10,000 and 1 million individual stars. Those stars exert a gravitational attraction on one another. As a result, the stars in the cluster move through the universe as a group.

4.  A galaxy is a very large group of stars, planets, space dust, and gases held together by gravity.

a)      A galaxy contains billions of stars.

b)      Our solar system is part of the Milky Way galaxy. The stars you can see at night are part of the Milky Way. Our sun is only one of the many stars in our galaxy.

c)      The Milky Way Galaxy is a spiral galaxy with roughly 100 billion other stars. There are spiral arms and a bright central part. The sun is far from the center of the galaxy. It is halfway to the edge of the galaxy along the Orion spiral arm. It is 100,000 light-years across. We cannot see the spiral shape of the Milky Way Galaxy from Earth because we are located within one of its spiral arms.

d)      Galaxies have three main shapes.

s         Spiral galaxies have a dense grouping of stars in the middle surrounded by stars arranged in spiral arms. The stars of the Milky Way from a thick, barlike center, surrounded by a spiral of stars.

s         The stars in elliptical galaxies form shapes like balls or flat discs.

s         The stars in irregular galaxies do not form any particular shape. Irregular galaxies are less common. Scientists think most irregular galaxies were once spiral or elliptical galaxies, but their shapes changed over time because of gravity. Some irregular galaxies may have formed when two or more galaxies merged.

5. The stars making up a cluster travel together because of the gravitational attraction the stars exert on each other. Galaxies also exert a gravitational attraction on each other. This force can hold galaxies together in a group known as a galactic cluster. A cluster is made up of tens or hundreds of galaxies.

The Expanding Universe

1.  The big bang theory states that all matter and energy were once packed into a tiny particle smaller than a speck of dust. This particle was incredibly hot and dense. In an event called the big bang, the particle suddenly began to expand. In a fraction of a second, matter and energy were thrown rapidly outward in all directions. Over time, the universe cooled and continued to expand. As it cooled, the matter collected to form dust, stars, gas clouds, and planets.

a)      Evidence suggests the big bang took place about 13.7 billion years ago. More than 300,000 years later, matter began to form galaxies.

b)      According to some scientists, the movement of galaxies is evidence for the big bang. Observations show that most galaxies are moving away from each other. The galaxies are moving farther apart because the universe is expanding.

c)      Research indicates that galaxies are moving away from Earth by measuring the wavelengths of radiation from the galaxies.

d)      Wavelengths of light from a distant galaxy can be used to determine the distance between Earth and the galaxy. The light from distant galaxies shows a shift to longer wavelengths, and the shift increases as the distance increases.

e)      We know that galaxies are moving because of the light they give off. The light we see from most galaxies shows that they are moving away from Earth in all directions.

f)         Astronomers measure the wavelengths of radiation from galaxies to determine their movement.

g)       The Big Bang theory of the formation and expansion of the universe is supported by the observed red shift.  A red shift in the spectrum of the light from an object indicates the object is moving away from you.

2. In the 1920s, Edwin Hubble demonstrated that the farther away a galaxy is, the faster it is moving away from Earth. This pattern of motion supports the idea that the universe is expanding.

a.    Astronomer that proved that the “spiral nebulae” or fuzzy objects in space were distant galaxies

b.   Designed a system for grouping galaxies by their shape: elliptical, spiral, and irregular

c.    Discovered that galaxies are moving away from one another

d.   The size of the universe is increasing

e.    The Hubble Space Telescope, named after Edwin Hubble, was put into orbit in 1990. This telescope has been most useful to scientists studying the origins of the universe.

f. www.hubblesite.org

3.  The distance to most stars is so large that the units of meters and kilometers are not practical. Instead, scientists use a unit called a light-year to measure distances between stars and galaxies.

a)      A light-year is the distance that light travels in one year. In space, light travels at a speed of nearly 300,000 km/s or almost 9.5 trillion km/year. Therefore, 1 light-year equals roughly 9.5 trillion km.

b)      After our sun, the nearest star to Earth, Proxima Centurai, is a little more than 4.2 light-years away. Light from this star takes about 4.2 years to reach Earth. Proxima Centurai is almost 40 trillion km from Earth.

c)      The diameter of the Milky Way galaxy is about 100,000 light-years. One of the closest galaxies to the Milky Way, the Andromeda galaxy, is about 2.3 million light-years away. That is almost 22 million trillion km. Astronomers can observe galaxies as much as 13 billion light-years from Earth.

4. A telescope is an instrument used to study objects in space.

a)      Optical telescopes use lenses or combination of lenses and mirrors to gather visible light. They make distant objects appear closer and brighter.

b)      Other telescopes gather other electromagnetic (EM) radiation from objects in space. Recall that EM radiation is energy that travels through spaces as waves. It includes infrared light (heat), ultraviolet light (UV), X-rays, and radio waves.

c)      The use of early telescopes by astronomers---stars must be much farther from Earth than planets since they appeared as only points of light.

d)      Galileo---improved telescopes; over time advancements in technology has improved our understandings of our solar system and allowed a closer examination of the moon’s surface

e)      Fred Haise---astronaut from Biloxi; lunar module pilot on the aborted Apollo 13 lunar mission in 1970 (made into a movie)

Types of Telescopes

Microwave observatories----measure microwave background that is referred to as the remnant of the Big Bang by measuring the very small differences in temperatures from one place to another