Lesson 3December 6th, 2010

The Wave Nature of Light Light is a form of energy that travels in

waves. This kind of energy is also called electromagnetic radiation. Visible light is electromagnetic radiation that we can see with our eyes. There are other forms of electromagnetic radiation as well, including radio waves, microwaves, ultraviolet radiation, and X-rays. When visible light rays are split into a rainbow of colours, the result is called the visible spectrum.

The Wave Nature of Light The full electromagnetic spectrum,

ranges from radio waves with very long wavelengths, through visible light, to gamma rays with very short wavelengths.

Hubble’s Ideas Edwin Hubble was an American

astronomer who was one of the first scientists to study galaxies.

He made two great discoveries 1.He confirmed that there were many

galaxies besides the Milky Way. 2.He discovered that almost all galaxies

are moving away from each other. He discovered this by studying light spectrum.

The visible light spectrum is the rainbow band of colours into which white light separates when it passes through a prism.

A device called a spectroscope enables us to split a light sample into its spectral colours.

Each kind of light source has its own unique spectrum. Spectral lines are created as each gas element absorbs some of the light energy. Each element does this in a different way, creating its own particular pattern of spectral lines. By studying different light spectra, it is possible to tell a lot about the properties of the sources that produced them, even if those sources are extremely far away.

C8 Comparing Light Spectra 1. What differences did you notice about

the spectra for the different light sources? 2. (a) Which kind of light source produced

the most distinct spectrum of all the sources?

(b) Explain why you think that was the case. 3. How did the spectra from the gas

discharge tubes differ from the spectra displayed by the light sources?

4. How could knowledge of the spectra of light created by particular elements help an astronomer determine the composition of a distant star or galaxy?

Analyzing the Movement of Light Waves

Spectral shifting is the change in position of spectral lines to the left or the right of where they normally are in the spectrum of a light source that is not moving.

In the galaxies that Hubble was studying, the spectral lines were shifted toward the red end of the colour band.

The only way for spectral lines to shift this way is if the light source and the observer are moving away from each other at very high speed. A shift towards blue would be caused by moving towards each other.

Analyzing the Movement of Light Waves

This phenomenon is called the Doppler Effect. When an object is stationary, the waves move out evenly in all directions. When the object is moving the waves in front of the object become compressed and the ones behind lengthen.

Evidence for the Big Bang Theory By looking at the light spectrum of each

galaxy, Hubble was able to figure out the speed at which each galaxy was moving away from our own.

Then, for those same galaxies, he separately determined the distance between each one and the Milky Way. Hubble discovered a clear relationship between the distance away and the velocity.

The farther away a galaxy was, the faster it was moving away.

Evidence for the Big Bang Theory

This supports the idea of the expanding universe. This theory known as the Big Bang theory, states that the universe formed when an infinitely dense point suddenly and rapidly expanded in a single moment.

All the matter and energy that exists today was created during the early minutes of that hot, rapid expansion. It is thought that the universe formed 13.7 billion years ago. That moment marks the beginning of the universe and also the beginning of time.

Expanding Universe Example http://www.youtube.com/watch?v=IWbc54u8k8c

Using Microwaves to Map Cosmic Background Radiation Until 1965, a critical question related to

the Big Bang theory remained unanswered. The theory stated that the very early universe was extremely hot, filled with short-wave gamma ray radiation.

Then, as the universe rapidly expanded, it cooled and the wavelength of the radiation lengthened. The radiation became lower energy types, including Xrays, ultraviolet, visible light, infrared, and microwaves.

Using Microwaves to Map Cosmic Background Radiation A microwave antenna designed for

telecommunications discovered that this radiation did exist and that it came from all directions, not just stars.

In 1992 and 2006, satellites made detailed maps of the background radiation. The evidence collected supports the theory.

It is important to note that as galaxies move farther apart, gravity has less effect, thus causing the galaxies to move even farther apart at a faster rate.

Radiation Maps: Evidence for the Big Bang Theory

Stars: The View from Earth Some stars in the sky appear to be in grouped patterns. The best-known star pattern in the northern hemisphere is the Big Dipper. Different cultures around the world refer to this collection of seven stars by other names, such as the Plough, the Ladle, and the Great Cart.

The Big Dipper is part of a larger star pattern known as Ursa Major, which is Latin for Great Bear. Ursa Major is an example of a constellation.

Stars: The View from Earth A constellation is a group of stars that,

from Earth, resembles a recognizable form.

Astronomers have officially listed a total of 88 constellations. Examples: Cassiopeia, Orion, Pegasus.

Smaller recognizable star patterns within a larger constellation are known as asterisms.

The Big Dipper is an asterism. Star patterns like these are just one kind of astronomical phenomenon, Any observable occurrence relating to

astronomy. It is important to note that the stars are

at varying distances away.

How a Star Is Born All stars form inside a collapsing nebula, a

cloud of dust and gases. A nebula’s collapse can be triggered by

gravitational attraction of a nearby star or the shockwave from an exploding star.

The area with the largest mass starts to pull more mass in. The matter pulled in has excess energy which causes the central ball of material to begin to spin. Extremely high pressures build up inside the ball, which in turn causes the tightly packed atoms to heat up. As the temperature climbs, the core begins to glow. This is a protostar

A protostar is a star in its first stage of formation. Eventually, the temperature of the spinning protostar rises to millions of degrees Celsius. This is hot enough for nuclear reactions to start. Over tens of thousands of years, the energy from the core gradually reaches the star’s outside. When that occurs, the fully formed star “switches on” and begins to shine.

The Life Cycle of Stars - Star Mass and Evolution Astronomers describe stars in three

general mass categories: low, medium, and high.

The Life Cycle of Stars - Star Mass and EvolutionLow Mass Stars Low mass stars use their nuclear fuel

much more slowly than more massive stars do. Low mass stars burn so slowly that they can last for 100 billion year. This is due to less gravity and thus less pressure. The light from a red dwarf starts dim and gradually grows dimmer.

Eventually they collapse under their own gravity. Over time a red dwarf will turn into a

white dwarf.

Medium Mass Stars Medium mass stars burn their fuel faster

than low mass stars do, using their hydrogen up in about 10 billion years. When the fuel starts to run out the star slowly collapses under its own gravity. This raises the temperature enough to cause the fusion of helium and reignites the star. The star expands rapidly to a red giant. The fuel then runs out and the star slowly burns out.

High Mass Stars High mass stars are those that are more

than 10 times the mass of the Sun. In a high mass star, as gravity pulls matter into the

centre of the star and squeezes the core, the nuclear reactions accelerate. As a result, a high mass star is hotter, brighter, and bluer than other stars.

After a fuel runs out the star cycles through collapsing and using another fuel. The star will become a supergiant like Polaris and Betelgeuse.

Betelgeuse is so large that if it was in place of our sun it would reach Jupiter

Supernovas: The Violent End of High Mass Stars After a star cycles through different

fuels it eventual reaches iron. When all of the other fuels burn out, the star will essentially go out. The star then collapses with so much energy that it heats up to over a few million degrees and explodes. (Supernova)

High Mass Stars

The explosion is strong enough to create every element in the periodic table through fusion. Some of the fragments are sent far out into space while other debris may be made into new nebulae.

The star’s remaining core after a supernova explosion faces one of two outcomes, depending on the mass of the original star:

High Mass Stars • Neutron stars (mass between 10 and 40

times the mass of the Sun). A supernova explosion is directed not only outward, but also inward. This force causes the atoms in the star’s core to compress and collapse.

When an atom collapses, it forms neutrons, particles that are at the centre of most atoms already. When the star’s core becomes little more than a ball of neutrons only about 15 km across, it is called a neutron star. Neutron stars are made of the densest material known

High Mass Stars

Black holes — If the star was more than 40 times the mass of the Sun, it will become a black hole.

After exploding as a supernova, the star’s core is under so much gravitational force that nothing can stop its collapse, not even the formation of neutrons. In this case, the effect of gravity is so great that space, time, light, and other matter all start to fall into a single point.

The life Cycle of a Starhttp://www.youtube.com/watch?v=YU6X3SPZAJo&feature=related

The Hertzsprung-Russell Diagramhe stars are arranged by three classifications. 1.By colour – Red stars are plotted on the

right, and blue stars are plotted on the left. Other stars, such as the yellow Sun, are plotted in between.

2.By luminosity – The brightest stars are plotted at the top, and the dimmest stars are plotted at the bottom. A star with a luminosity of 100 is 100 times brighter than the Sun.

3.By surface temperature – The hottest stars are plotted on the left, and the coolest stars are plotted on the right.

The Hertzsprung-Russell Diagram

Starry Night ActivityUsing a Star Chart Instead of using a star chart we will

use a program called starry night to replicate what we would be able to see from Moose Factory at night.

Question How is it possible to locate the

positions of stars in the night sky?

Starry Night ActivityUsing a Star Chart2. Locate the Big Dipper. Identify

it first on your star chart. It is part of the constellation Ursa Major and has the shape shown below. Then, find the Big Dipper in the sky. You will see many more stars in the sky than appear on the chart, but the bright stars making up the Big Dipper should standout.

Starry Night ActivityUsing a Star Chart 3. After you find the Big Dipper,

locate the two stars that make up the outside of the ladle. These are know as the “pointer stars” because they point to Polaris, the North Star. Follow the pointer stars until you see a reasonably bright star. This is Polaris. It is always in this position in the sky no matter what the season or the time.

Starry Night ActivityUsing a Star Chart 4. Follow along an arc until you

reach a group of five stars that forms a big W. (Depending on the time of night and the season, this may look more like an M.) This is the constellation Cassiopeia.

Starry Night ActivityUsing a Star Chart 5. Finally, go back to Polaris. It

is part of the Little Dipper, forming the last star in the handle. The stars of the Little Dipper are not quite as bright as the stars of the Big Dipper, but they are still easily visible with the naked eye

Starry Night ActivityUsing a Star Chart 6. Describe how you used the Big

Dipper to find Polaris, Cassiopeia, and the Little Dipper.

7. If you were unable to find any of these stars or groupings, explain what problems occurred that prevented you from locating them in the sky.

8. The star Sirius is brighter than Polaris. Would it make more sense to call Sirius the North Star, instead of Polaris? Explain your answer.

Questions

1. What is a spectrum? K (1) 2. What is the name given to the generally

accepted scientific theory that describes the origin and evolution of the universe? K (1)

3. How is it possible to know that the element hydrogen exists throughout the universe? I (1)

4. How does the idea that space itself is expanding relate to the observation that the spectra from distant galaxies are red-shifted? I (1)

5. What main property of newly formed stars determines how the star will evolve? I (1)

6. What process must occur inside a forming star before it can “switch on,” creating its own light? K(1)