To Infinity and Beyond!Chapter 3

Origin of the Universe

• Many people theorize how the universe was formed. There has not been one explanation that has been made into scientific law pertaining to this topic. 3 popular theories are:– Steady state theory: universe always existed as it is today

and it always will. It does not grow – Oscillating model: the universe began with expansion, over

time the expansion slowed and the universe contracted then the cycle began over again

– Big bang theory: the universe started with a big bang and has been expanding ever since

At the beginning there was Gravity!pg 108

• Scientist think that all solar systems begin as clouds of materials that accretion slowly joins and gravity holds them together

• Accretion is the process of building something up gradually by the gathering together of smaller pieces.

• Gravity, together with accretion make solar systems, stars, planets, and holds them all together

Galaxies

• The stars in constellations all belong to a galaxy. The galaxy in which we live in is called the milky way galaxy

• A galaxy is a large collection of stars, gas, and dust held together by gravitation.

• The sun and our solar system are inside the milky way galaxy. It is believed that the milky way has one trillion stars!!– Many other galaxies also exist in the universe

Major types of Galaxies

• See page 102

What keeps everything in place? • GRAVITY!!!• Newtons law of universal gravitation states that every

object in the universe attracts every other object!• Earth orbits the sun because of the suns gravitational pull!• The strength of the gravitational pull depends on the mass

of each object. Gravity is also affected by distance. (the farther away the less gravity)

• Intertia keeps everything from crashing into each other. See page 106

• Gizmo Gravity Pitch

Constellations• A constellation is a pattern of stars that is

named as a group. – The stars that make up constellations in reality,

have no relation to each other. (look this way because earth is round like a convex lenses)

– They form an imaginary shape or figure in the sky.

Modern Constellations• Modern astronomy divides the sky into 88

constellations, many of which you may know (big dipper, little dipper, etc)

• Polaris, is also known as the North Star, it is used to guide travelers and as a point of reference in the sky. It is positioned directly over the north Pole!

Circumpolar Constellations• As Earth rotates, Ursa major, Ursa

minor, and other constellations in the northern sky rotate around Polaris. Because of this, they are called circumpolar constellations. – The constellations appear to move

because earth is in motion. They complete one full circle in the sky in about 24h

• As earth orbits the sun, different constellations come into view while others disappear. Because circumpolar constellations always orbit Polaris they are visible ALL year long while others are not.

Binary Stars pg 100

• Some star systems have two stars or double stars called binary stars

• Often, one is much brighter and more massive than the other.

• Astronomers can detect this by observing the effect of gravity one has on the other. The dim stars gravity causes the bright star to wobble!

Absolute and Apparent Magnitudes• When you look at constellations, you’ll notice that some

stars are brighter than others. Why do you think this happens?

• The Absolute magnitude of a star is the measure of the amount of light it gives off

• Apparent magnitude is a measure of the amount of light received on Earth

• A star that is dim can appear bright if it is close to Earth, and a start that’s bright can appear dim if its far away.

• If two stars are the same distance away, what might cause one of them to be brighter than the other?

Parallax pg 95

• How do scientist determine the distance from Earth to nearby stars?

• Parallax- the apparent shift in the position of an object when viewed from two different positions.

• One eye closed thumb out demonstration• The nearer an object is to the observer, the greater its parallax is. • Astronomers can measure the parallax of relatively close stars to

determine their distances from Earth. Knowing the angle that is changing and the size of Earth’s orbit, astronomers can calculate the distance of the star from Earth.

• Look at the diagram

Measurement in space and Scientific notation pg 96• Because space is so vast, a special unit of measure

is needed to record distances. Distance between stars and galaxies are measure in light years.

• A light year is the distance that light travels in one year. – Light travels at 300,000 km/s or about 9.5 trillion km in

one year. – The nearest start to Earth other than the sun is Proxima

Centauri which is 4.3 light years away or about 40 trillion km!!!

Difference between planets pg 99• A Star is a giant ball of gas, primarily hydrogen

and helium, which undergoes nuclear fusion. Our sun is a star

• A planet is an object that orbits a star, is large enough to have become rounded by its own gravity and has cleared an area for orbit.

• Solar systems contain both planets and stars and can also be referred to as planetary systems.

Properties of stars pg 111-113

• The color of a star indicates its temperature.– hot stars are a blue-white color– Cool stars are orange or red– Stars with the same temperature as our sun have a yellow color

• Astronomers study the elements in stars by observing their spectra.– A spectroscope is an instrument that separates light into its

component colors. – A stars spectra is like its fingerprint it is unique to that star only.

It identifies the elements in the star; most stars are composed mainly of hydrogen and helium

Gizmo

• Star Spectra

Classifying stars 114• Like people, stars are very

different from each other. They vary in age, size, temperature and brightness.

• In the early 1900’s Ejnar Hertzsprung and Henry Russell observed that in general, stars with brighter temperatures also have brighter absolute magnitudes

• The following diagram is called the Hertzsprung-Russell (H-R) diagram and it shows the relationship between temperature, brightness and magnitude.

The main sequenceLook at the H-R diagram handout• Most stars on the H-R diagram fit into a diagonal band. This

band is called the main sequence. It contains hot, blue, bright stars in the upper left and cool, red, dim stars in the lower right.

• 90% of all stars are main sequence stars but there are a few that don’t fall into this “line” what are they?

• White dwarfs are stars that are dying. They have lost all of their energy and gas for different reasons and so they are small, hot, but not bright

• In contrast, super giants, and giants are stars that extremely large and red. They are usually called red giants.

Gizmo

• H-R Diagram

How do they shine?• Reactions between the nuclei of atoms create the

energy and light in stars. – Our sun has very high concentrations of hydrogen, given

its’ extremely high temperature. In 1930, scientist theorized that hydrogen fused to make helium because of the extreme temperature thus releasing tremendous amounts of energy.

– Years earlier, Albert Einstein theorized that mass could be converted into energy. He created the famous equation E=mc2• E= energy, M= mass, and C= speed of light. The small amount of

mass “lost” when hydrogen atoms fuse to form a helium atom is converted to a large amount of energy.

Life cycle of a star 117 -121• Like all living things, nothing lives on forever.

Since stars are powered by hydrogen, eventually it will run out and the star will die.– Our sun has a life span of about 10 billion years it

has only lived half of its life.

Expansion of the Universe; Doppler effect• Most of the theories suggest that the universe

is still expanding or has expanded but how do we prove it? – Doppler shift: similar to Doppler effect; when stars

move away from Earth the wavelengths of light are stretched. If you analyze them thru a spectroscope you see shifts in the dark lines. When a star is moving towards earth the lines shift to the blue side and when a star is moving away from earth the lines shift to the red side.

Further proof; red shift

• In 1929, Edwin Hubble questioned the meaning of the red shift of light coming from other stars to earth. All galaxies beyond the local group show a red shift in their spectra. If all galaxies outside the local group are moving away from Earth, then the entire universe must be expanding!!

• Balloon demo

Big Bang Theory further explained• With the discovery of the red shift, scientist

confirmed their belief in The big bang theory. Today, it is the leady theory about the formation of the universe.

• Whether the universe will expand forever to stop expanding is still unknown. If enough matter exist, then eventually the universe will begin to contract to a single point. However, studies of dark energy indicate that the universe is expanding faster !