Chapter 30, Star, Galaxies, and the Universe California Standards 2a., b., c., 1.e., & d. Chapter 30, Star, Galaxies, and the Universe

Stars and our sun A star is a ball of gases that give s off a lot of energy Stars are defined by their luminosity and temperature. The hotter stars are blue while the cooler stars are red. Our sun is yellow so it is an intermediate star as far as temperature.

Color Spectrum A spectrum is a series of colors or lines which indicate what a star is made of. Each star has a unique spectrum to that star. An astronomer can tell how hot the star is and what elements, such as helium, calcium, hydrogen, etc. is in the star.

Temperature of Stars The temperature of a star can be determined by its color. Temperatures can range from 2,800o C to 24,000o C. Blue stars are the hottest and red stars are the coolest. Our star is yellow and about 5,500o C

Temperature of Stars Low frequency, low energy High frequency, high energy

Temperatures of Stars Hottest Coolest

Omega Centauri globular cluster

Stars Composition A stars composition or what it is made of can be determined by it color. All elements have a certain color. Oxygen has a given color, hydrogen has a certain color, etc. The two most common elements in stars are hydrogen and helium.

Star Size and Mass Our sun is a medium size star and has a diameter of approximately 1,390,000 km. Other stars are more massive and can be 1,000 larger than our sun.

Stars Constellations are groups of stars named after mythological or familiar objects. There are 88 constellations Ursa Major, Big Dipper or big bear Ursa minor, Little Dipper or little bear Polaris, North Star

Apparent Motion of Stars The apparent motion of the stars is due to the movement of the Earth. The circular motion is due to the rotation of the Earth on its axis around the North Star called Polaris. The seasonal movement is due to the revolution of the Earth around the sun.

Circumpolar Constellations Constellations that circle the North Star, called Ursa Minor or Little Bear, are called circumpolar constellations.

Polaris the North Star in Ursa minor. Little Dipper, Ursa minor, with the North Star or Polaris Big Dipper, Ursa Major

Actual Motion of Stars Thanks to Edward Hubble, we have known that stars are actually moving away from us due to the Big Bang Theory. This movement away is called the Doppler effect or red shift due to the wavelength of light as a star moves away from the observer.

Edwin Hubble

The questions Hubble asked in 1919 How old is our universe? How big is our universe?

Mount Wilson Observatory

How big is our universe? Our universe is expanding. It is expanding at an accelerating rate. The current theory is the Big Bang Theory. What is causing it to expand at an acelerating rate?

Color and Wave Length of Light

Doppler Effect or Red Shift

Expansion of the Universe Started with the Big Bang. Occurred approximately 15 billion years ago. Is the Big Bang still the current theory as to the formation of the universe?

Movement of Galaxies Galaxies are moving away from a central point Edward Hubble in 1924 proposed this theory Based upon Doppler effect

Magnitudes of Stars/Galaxies Absolute Magnitude – the absolute or actual amount of light the star gives off. Apparent Magnitude – The amount or observed amount of light on Earth.

Distances to Stars/Galaxies Parallax – Shift in position of an object when viewed from two different positions. Light year, distance light travels in one year.

How Far Does Light Travel in One Year? 9,460,800,000,000 km or 9.46 X 1012 km or 10 X 1012 km Whoa Baby that’s a lot of klicks!!!

Parallax, ‘para’- meaning two

Parallax

Stellar Evolution Astronomers have developed theories as to life cycles of star formation. The H-R diagram describes this theory with luminosity versus temperature of a stars life cycle. Luminosity = brightness

Stellar Evolution Stars start out as a cloud of gas and dust called a nebula. As density and temperature increase the nebula, through nuclear fusion becomes a main-sequence star. Giants and white dwarfs are stars that are not in the main-sequence of the H-R diagram.

H-R Diagram

Main Sequence Stars

Energy Source for the Stars Energy is produced by the fusion of hydrogen into helium. This takes place at 10,000,000 degrees Kelvin Other elements are created also such as calcium, iron, etc. Occurs when temperature and pressure are great enough.

All stars are not alike. 1. The sun is a small, cool star 2. The sun is called a main sequence star. Meaning that it is just an average star in size and age. 3. There are much larger stars in the universe. 4. These larger stars are called supergiants.

How large is our Sun? supergiant

A Stars Life Cycle White dwarfs and giants are in the final stages of a stars life cycle. A star that explodes at the end of its life cycle is called a nova. A very large star, eight times the mass of our sun, when it explodes is called a neutron star.

A Stars Life Cycle A neutron star that emits a radio waves that sweeps across the universe is called a pulsar. A star that collapses in onto its self and whose gravity is so huge that not even light can escape is called a black hole.

Galaxies

Three Types of Galaxies 1. Elliptical Galaxies 2. Spiral Galaxies 3. Irregular Galaxies

Elliptical Galaxy

Spiral Galaxy

Triple Spiral Galaxies

Irregular Galaxy

Milky Way Galaxy Double Arm, Spiral Galaxy.