1. CHAPTER 28 STARS AND GALAXIES

2. 28.1 A CLOSER LOOK AT LIGHT
Light is a form of electromagnetic radiation, which is energy that travels in waves.
Waves of energy travel at 300,000 km/sec (speed of light
Ex: radio waves and x-rays

3. Electromagnetic radiation waves are arranged into a continuum call the electromagnetic spectrum.
Wide range of wavelengths
Long wavelengths with low frequencies at one end, short wavelengths with high frequencies at the other end
Wavelength measured crest to crest/trough to trough
Frequency the number of that crests of the same wavelength that pass a point in one second.

4. Scientists study the visible light portion of the electromagnetic spectrum.
Spectra of a stars allow for astronomers to learn about the star’s elements and motion.
Spectra studied using a spectroscope

5. Three types of visible spectra
Continuous spectrum: unbroken band of colors, emitting all colors of visible light
Emission spectrum: unevenly
space of lines of different colors,
emitting light of only some
Wavelengths
Absorption spectrum: dark lines that
cross a continuous spectrum.

6. Doppler Effect - change in the wavelength of sound due to motion between the object and the receiver.

7. Doppler effect applies to lights as well as sound.
Shift of the emission spectra can indicate if the object is moving towards or away from Earth
Shift towards red end of spectrum, object moving away Earth – Redshift
Shift towards blue end of spectrum, object moving towards Earth - Blueshift
Doppler effect determined that the universe is expanding

8. TELESCOPES
Optical Telescopes – gather far more light than an unaided eye and magnify imagers
Reflecting
Uses one lens at back to gather and focus light
Image reflected on to a small mirror and then the eye piece
Refracting
Uses two lenses
Lens at the front gathers light
Eyepiece magnifies image

9. Radio Telescopes = big satellite dishes
Use to detect energy waves at frequencies lower than visible light
Other
Usually satellites in space
Gamma ray
Background radiation
X-ray
Hubble (infrared)

10. 28.2 Stars and Their Characteristics
Observation of stars has been going on for over 5000 years
The grouping of stars are called constellations
Constellations
only appear together as viewed from Earth; from a different angle they do not look like the constellation

11. Constellations (continued)
Constellations will change shape over thousands of years due to the universe expanding
Move across the sky from east to west (though Earth rotates west to east)

12. North Star – Current is Polaris
Sits directly over the North pole
Does not move to the naked eye
Very powerful tool for navigation
Due to Precession, Polaris will not always be the “North Star”

13. The Constellations that dominate the night sky change from month to month. This is the result of the Earth’s change in position as it orbits the Sun.

14. Distances to stars and other objects in space
Astronomical Unit (AU) - the distance from Earth to the Sun (150 million kilometers)
Light year - the distance light travels in one year (9.5 trillion kilometers)
It is a distance measurement
Example light-years means that the light we see has been traveling for 4.2 years before we can see it (4.2 X 9.5 trillion km)
Parallax - change in an object’s direction due to a change in the observer’s position
Parsec short for “parallax second” equal to light-years.

15. Parallax
The further the object from the viewer, the less the parallax shift.

16. Stars Elements No two stars have the same proportions of elements
Hydrogen ~69%
Helium ~29%
Heavier elements ~2%
light that radiates is dependent on composition and temperature, this differs in every star
Star spectrum is its fingerprint

17. Mass, Size and Temperature
Stars vary greatly in masses, size and temperature
Cannot observe directly so we are estimating what the mass might be
Gravitational effect on bodies around the star help with estimating its mass
Star mass is expressed as multiples of the mass of our Sun (which has a stellar mass of 1)
Size varies more than mass
Smallest stars are smaller than Earth
Largest have diameters more than 2000 times that of our Sun
Stars differ even more in density
Betelguese is about one ten-millionth of our Sun
One star is so dense that one teaspoon would weight more than a ton on Earth

18. Star size comparison

19. Temperature of stars vary
Range of color emitted is dependent on the surface temperature
Cool stars are red
Ex. Betelguese with a surface temperature of 3000oC
Mid-temperatures are yellow
Ex. The Sun with a surface temperature of 5500oC
Hot stars are blue
Ex. Sirus
Harvard Spectral Classification Scheme - group stars by temperature and color

21. Luminosity = brightness of a star
Dependent on size and temperature of the star
If two stars are the same size the hotter star would be more luminous
Apparent magnitude - how bright a star appears
Does not factor in distance
Absolute magnitude - how bright the star would be if all stars were the same distance from Earth (10 parsec)

22. Variable stars -show a variation in brightness
Cepheid variables are yellow supergiant stars with a cycle of brightness ranging from days.
Most have a cycle of 5 days.
Nonpulsating star change in brightness due to fact that it is more than one star.

23. 28.3 LIFE CYCLE OF STARS
Hertzsprung-Russell (H-R) diagram – shows luminosity, temperature, and stages in the life cycle of the stars
Main Sequence – 90% of stars run in a band from upper left to bottom right of diagram
Giants & Supergiants – more luminous, found above main sequence
White dwarfs – near the end of their lives, below main sequence, glowing stellar core

24. Hertzsprung-Russell Diagram

25. Life cycle of a star like our Sun
A star begins its life in a cloud of gas ( mostly Hydrogen) and dust called a nebula
nebula condenses, becomes denser, temp. increases  becomes a protostar fusion begins and star is “born”
Hydrogen in core continues to fuse into helium
When hydrogen “runs out”, fusion occurs outside the core and the star expands (giant)
Gas layers are blown away and the carbon-oxygen core is left (a white dwarf)

26. Life cycle of a Massive Star
Begins like our sun
Instead of a carbon-oxygen core forming, an iron nuclei forms, and the star expands to 100x the size of our sun (supergiant)
Iron nuclei absorbs energy and collapses (supernova)
Massive star remnants become a Neutron Star or Black Hole

27. http://www. teachertube. com/viewVideo. php
(about 9 minutes)

28. Galaxies and the Universe
Universe –everything that exists, 10 billion-20 billion years old
Galaxy – group of stars held together by gravity
3 types:
We live in the Milky Way Galaxy ( a spiral galaxy)
Elliptical Galaxy- concentrated, spherical shape
Irregular Galaxy – smaller, fainter, spread unevenly

29. 3 types of galaxies SPIRAL GALAXY (MILKY WAY) ELLIPTICAL GALAXY
IRREGULAR GALAXY

30. Origin of the Universe
Big Bang Model – explains the history of the universe from a fraction of a second AFTER it came into being up to present time
Evidence supporting it = distance between galaxies is increasing (universe is expanding)
Edwin Hubble found redshifts in the spectra of the galaxies
Cosmic background radiation found with radio telescopes