Reviewing the UniverseReviewing the Universe

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1. The entire celestial cosmos (everything in

space), an orderly and harmonious system, is

known as the universe.

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Big Bang Theory

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Big Bang (q. 18)• Big Bang Theory, currently accepted explanation of the

beginning of the universe. • A cosmic reaction, called the big bang, occurred about

13.7 billion years ago, and the universe has since been expanding and cooling

• Once extremely compact, dense, and hot. This would have released radiation, and that radiation should still be visible today.

• American astronomer Edwin Hubble provided some of the greatest supporting evidence for the theory with his 1929 discovery that the light of distant galaxies was universally shifted toward the red end of the spectrum.

• Proved that the galaxies were moving away from each other.

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Support

• Red Shift– Another cause of red shift is the

expansion of the universe, which explains the observation that the red shifts of distant galaxies, quasars, and intergalactic gas clouds increase in proportion to their distance from the earth. This mechanism is a key feature of the Big Bang model of physical cosmology

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What is the red shift?

• An observed red shift due to the Doppler effect occurs whenever a light source moves away from the observer.

• Astrophysics uses Doppler red shifts to determine the movement of distant astronomical objects

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Big Bang

The radiation was found in the 1960s, by complete serendipity, by a researcher at Bell labs trying to determine the source of interference in trans-Atlantic telecommunications. As it turned out, a strikingly uniform source of microwaves was coming from everywhere in the sky - and it had a corresponding temperature of 2.7 Kelvin. This was the discovery that vindicated the Big Bang theory. Still, it's hardly the only one.

There is nuclear evidence in the elements (hydrogen, helium, carbon, etc.)

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Radiation Map of the Universe

Astronomy probe5-yr mission

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2. Within the universe, there are masses of closed gravitational systems of stars and their satellites, nebulae, and dust that are spinning and traveling

through space. These are known as galaxies.

3. There are three main kinds of galaxies:

Spiral Elliptical Irregular

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4. The galaxy in which we live is called the Milky Way.

The Milky Way has about 200 billion stars in it

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How is a galaxy formed?• All galaxies began forming at about the same time

approximately 13.7 billion years ago. • They formed from huge gas clouds larger than the resulting

galaxy. The clouds began collapsing because their internal gravity was strong enough to overcome the pressure in the cloud.

• If the gas cloud was slowly rotating, then the collapsing gas cloud formed most of its stars before the cloud could flatten into a disk. The result was an elliptical galaxy .

• If the gas cloud was rotating faster, then the collapsing gas cloud formed a disk before most of the stars were made. The result was a spiral galaxy.

• Irregular galaxies are clouds/stars that began to form in the swirling disk of gas and the system began to be recognizable as a galaxy. These early galaxies are very rich in gas, rather irregular in shape and speckled with extremely luminous blue stars.

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Galaxy Formation

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5. Also, in the universe, there are billions and

billions of stars.

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6. Stars are classified

according to their color,

temperature, and magnitude (brightness).

This information is displayed on the

Hertzsprung-Russell Diagram.

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7. A star’s brightness is

referred to as its magnitude. There are two ways to think

about this:

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a. Absolute magnitude is the amount of light that is actually being emitted from a star.

b. Apparent magnitude is the amount of light that is actually being seen on earth (this may depend on how far away the star is from us).

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Measuring distance to nearby stars

• We use a parallax effect– It is the angle through which as star appears to

move – Geometric function

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8. The most common (90%) kind of star in the universe is known as a main sequence star. Our sun is an example of this kind of star.

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9. Stars are “born” in a part of the universe called a nebula.

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10. As they age, several things can happen to stars. In the end, most stars grow to become red giants (or super giants if they are exceptionally massive.)

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11.When they “die,” stars can become:

a. Black holes (the most massive stars end their life this way)

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b. Neutron stars (stars of high mass become this)

Neutron stars pack roughly the mass of our Sun into a region the size of a city. Here's a comparison with Chicago:

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C. White dwarfs and eventually black dwarfs (what the least massive stars will become, like our sun)

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12. The more massive stars explode before they become neutron stars or black holes. This incredible sight is referred to as a supernova.

This is a photograph of Supernova 1987 a, one of the only ever witnessed.

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13. The second closest star to us is called Alpha Centauri, which is 4.3 light years away. Although it appears as one bright light, it is actually three separate bodies!

Here is how the three stars that make up Alpha Centauri compare to the sun.

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Many stars are like this… when there are more than one “body” that we see as one light, the stars are called companions (because they go together).

The Chandra image shows Mira A (right), a highly evolved red giant star, and Mira B (left), a white dwarf.

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Two stars like this are called binary stars, the prefix bi- means “two” (like a bicycle). Mira (shown here) is an example of such a star system.

The companion star to Mira is referred to as Omicron Ceti A.

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Star’s Energy

• Fusion drives the existence of a star

• A star releases huge amounts of energy.– Energy is released in the form of

electromagnetic radiation.

• A star is a mass of gas held together by its own gravity.

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14. Because the universe is so big, scientists have to use a measurement of distance known as a light year , which is how far light can travel in one earth year.

Interesting Facts About Light Years:•It takes 8.3 minutes for light to travel from the Sun to the Earth (a

distance of 1.58 ×10-5 light years).•The most distant space probe, Voyager 1, was 13 light hours away from

Earth in September 2004. It took the probe 27 years to cover that distance.

•The center of our galaxy, the Milky Way, is about 26,000 light years away. The Galaxy is about 100,000 light years across.

•The Triangulum Galaxy (M33), at a bit under 2.6 million light years away, is the most distant object visible to the naked eye.

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Unfortunately, we can’t travel that fast (yet?), but if we could, Einstein thinks several changes would happen to us:

a. We would become more massive.b. We would shrink in length.c. Time would pass slower.

This is outlined in his Theory of Relativity, which explains how mass, distance, speed, and time are interrelated - a strange concept to think about!

See an example of what Einstein means… http://www.pbs.org/wgbh/nova/einstein/hotsciencetwin/index.html

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15. People have studied the stars for thousands of years. In doing so, they have identified groups of stars that appear to form pictures in the sky. These are known as constellations. There are 88 identified constellations in all - most of which have some sort of story or myth associated with it.

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16. The North Star is always visible from our viewing point on earth; it is also known as Polaris (like the shopping mall).

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17. One of the most influential instruments (if not the most influential) in discovering what we know about the universe is the Hubble Telescope.

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The Bigger Question

• Does it end?– The Big Freeze of Heat

• Expands to be too cold for life

• Reaches temp minimum

– Big Bounce• Collapses then recreates

– The Big Rip• Ripped apart by energy sources

– The Big Crunch• Collapses upon itself