Stars – TemperatureStars – Temperature

• Hotter objects emit shorter wavelengths

• Cooler objects emit longer wavelengths– Ex. Sun is a “medium hot” (5800 K or about

5500 C) star and emits X-rays– Cooler stars emit infrared– Determining surface temperature by

maximum emitted wavelength (Wien’s Law)

– *NOTE: 0 degrees Celsius = 273 Kelvin; – -273 degrees Celsius = 0 Kelvin

• • 25,000 K: star looks blue• • 6,000 K: star looks yellow (like our sun)• • 3,000 K: star looks red

• Chemical composition of burning gas– Determined by passing light through a prism to generate a

spectrum– Light passed through nebula may have absorption lines– Ex. Sun is 74% Hydrogen, 25% Helium, 1% Other

• Spectral Class – combination of temperature and chemical composition– Signified by a letter O, B, A, F, G, K, M (hottest to coolest) – Our sun is G2

Stars – ColorStars – Color

Stars – Finding Distance by Stars – Finding Distance by BrightnessBrightness

• Why do you think stars would be different brightness levels?

• Apparent Brightness – combination of energy emitted and distance from Earth, brightness decreased by square of distance.

• Intrinsic Brightness – known as LUMINOSITY, measured in watts.

• If you know the apparent and intrinsic brightness, you can figure distance.

Star EvolutionStar Evolution

• Group 1 – Star Formation “Birth” (11-1)• Group 2 – Star Energy – Helium Fusion • Group 3 – Stellar Structure and Energy

Transport (11-3)• Group 4 – “Why is there a Main Sequence?”

(p.262-267)• Group 5 – Post-Main-Sequence Evolution (12-2)• Group 6 – Evidence of Evolution: Star Clusters

(12-3)

Stars – Motion Determined by LightStars – Motion Determined by Light

• Doppler Effect – Motion of a light’s source affects its observed wavelength of light– Approaching observer, waves compressed,

shortened wavelengths (BLUESHIFT)– Moving away from observer, waves spread

out, lengthened wavelengths (REDSHIFT)– Perpendicular motion to observer does not

shift the wavelength

Remember that old commercial?Remember that old commercial?

• Draw a person or an ear to represent the observer.

• Animations of Doppler Effect

EW: We are going to be EW: We are going to be reviewing today for the final next reviewing today for the final next

Monday. Monday.

Write down what the big bang Write down what the big bang theory and evidence for it are. theory and evidence for it are.

Tuesday, June 3Tuesday, June 3rdrd, 2014, 2014

LT: I will be able to discuss the big bang theory, evidence for it and star life cycles.

Agenda:

-Review for final next week

-can use note card on final

Tomorrow:

-Climate Change

• Origins– began with a large explosion called the

big bang theory– only energy before this, no matter– first hydrogen and helium were formed– larger elements were formed later by stars

The Big Bang TheoryThe Big Bang Theory

Big Bang TheoryBig Bang Theory

• Expansion indicates a denser, hotter past – uniform, hot gas that cools as it expands

• NOT an explosion from a point, but a simultaneous expansion from all places

• 13.7 billion years ago

Big BangBig Bang

• EVIDENCE – 1. Cosmic microwave background radiation – “noise,” same in all

directions • 1965 Arno Penzias and Robert Wilson

2. Expansion measured by Hubble constant • Distant galaxies are redshifted (based on electromagnetic spectrum)

– This is the doppler effect being applied to light • 1929 Edwin Hubble

3. most elements in universe are H and He (light elements)• Created during first moments of Big Bang • when stars reach the end of their life cycle, they distribute C, O, and

Fe into the universe • if the universe was older, there would be more C, O, and Fe

Expanding UniverseExpanding Universe

• All distant galaxies are redshifted. What does this mean about their distance from us?

• Hubble Law – further away a galaxy is, the faster it is speeding away

• If we can determine how fast the universe is expanding (aka Hubble constant), we can determine the AGE OF THE UNIVERSE!

Continuation of Expanding Universe

is expanding, therefore must have been smaller at one point

• evident by galaxies’ red shift– most look red because they are moving away from us

• if they were moving towards us, they would look bluer (blue shift)

Observers looking at an object that is moving away from them see light that has a longer wavelength than it had when it was emitted (a redshift), while observers looking at an approaching source see light that is shifted to shorter wavelength (a blueshift).

Cosmic background radiationCosmic background radiation– scientists found “noise” in

our galaxy that was the cosmic microwave background radiation predicted by the Big Bang theory

– The radiation can only be detected with a radio telescope which makes it show as a faint glow.

– Thermal radiation thought to be left over by Big Bang

– Happened 300,000 years after The Big Bang (so still about 13.7 billion years ago!)

Radio waves are a form of electromagnetic radiation, just like visible light!

How they work?

-waves bounce off a radio telescope, with this information computers can make images of the sky!

What is a radio telescope? What is a radio telescope?

Can make images like this of Can make images like this of our Universe! our Universe!

New Evidence!New Evidence!

Theory of inflation

-first proposed in 1980’s but recently found evidence for it!

-Found evidence that the universe was expanding exponentially seconds after the Big Bang

Life Cycle of StarsLife Cycle of Stars• Our sun is an average

star in our solar system! • life cycle varies

depending on the size• For most stars, 90% of

life cycle is spent fusing hydrogen that turns into helium

• all begin life inside a huge cloud of gas (mostly hydrogen) and dust called a nebula

When an average star ends its When an average star ends its “life cycle”!“life cycle”!

– hydrogen fusion stops – Fusing of helium begins to

create heavier elements (like oxygen, iron) • no more energy exploding

outward• gravity pulls matter inwards• First makes a large “red

giant” • outer layers often expand

and drift away creating a planetary nebula

• VERY high density, bright, and is called a white dwarf

Life cycle of Larger StarsLife cycle of Larger Stars

• for larger stars– elements up to iron are fused together– eventually may turn into a supernova

• quickly collapses because run out of energy and gravity is now the strongest force

– core collapses and then rebounds outward with a shock wave that makes a bright explosion (supernova)

– at this point, the heavier elements are finally created• if the leftover core is very, very dense, it may form a very

small neutron star or a black hole with VERY powerful gravity

CosmologyCosmology

• How did the cosmos begin, and what will happen to it?

• Study of the history and future of the universe

• Universe = everything that exists in space and time