Beyond our Solar System Earth Science Ch. 25 The LAST Chapter!!!!! Beyond our Solar System

25.1 Properties of Stars The sun, our closest star, is about 93 million miles away from Earth. By comparison the next closest star to the Earth, Proxima Centauri, is 24 billion miles from Earth. The light from the sun takes 8 minutes to reach Earth. The light from Proxima Centauri takes 4.3 years to reach Earth.

A constellation is used to designate an area of the sky that contains a specific pattern of stars. The nighttime sky is divided into 88 separate constellations.

Characteristics of all stars They absorb all of the radiation that strike them. They give off the maximum amount of energy possible at a give temperature. The energy of radiation given off by stars depends on temperature The color of a star gives a clue to its temperature

The hottest stars appear blue. Cooler stars appear red. Stars with temperature between 8,500° and 10,300°F appear yellow like our sun

hottest coolest

Binary stars are stars that orbit each other. Binary stars can be used to determine star masses.

Measuring Distance to Stars The most basic way to measure star distance is parallax Parallax is the shifting in the apparent position of a nearby star Parallax is determined comparing the current location of a star with the location 6 months later. The nearest stars have the largest parallax. Distant stars have a parallax that is too small to measure.

The distance to stars is measured in light years. Light years are measures of distance, not time. A light year is the distance light travels in one year. One light year is equal to 6 trillion miles

Stellar Brightness Magnitude is the measure of a star’s brightness A star’s brightness as it appears from Earth is called it’s apparent magnitude. Apparent magnitude is determined by 3 factors How big the star is How hot the star is How far away the star is When ranking the apparent magnitude of a star, the brighter the star, the smaller the number

The absolute magnitude of a star is a measure of how bright the star actually is. The absolute magnitude is not usually the same as the apparent magnitude To determine absolute brightness, astronomers determine what magnitude the star would have if it was at a standard distance of 32.6 light years or 10 parsecs. Stars with an absolute magnitude lower than 5 are brighter than the sun. Luminosity refers to the total amount of energy emitted by a star.

Hertzsprung-Russell Diagram An H-R diagram shows the relationship between the absolute magnitude and temperature of stars 90% of all stars, including the sun, are main sequence stars.

Red giants and supergiants are found in the upper right corner of the H-R diagram. These stars are not very hot but are very bright because they are large The white dwarfs are found in the lower part of the H-R diagram. These stars are very hot but are not very bright because they are very small.

25.2 Stellar Evolution Star Birth In the Milky Way, nebulae consist of 90% hydrogen, 9% helium, and less than 1% of the remaining heavier elements. Some nebulae become dense enough to contract due to gravity. Gravity pulls every particle in the nebulae toward the center. Gravitational force is converted into heat energy As the temperature increases a star is born

Protostar stage Occurs when the temperature of the nebula is hot enough to radiate energy from the surface. A protostar is a large red object A protostar is a developing star that hasn’t become hot enough yet to undergo nuclear fusion

Main sequence Stage Occurs when there is a balance between fusion and gravity The average star spends 90% of its life as a main sequence star Once the hydrogen fuel in the star’s core is depleted, it evolves rapidly and dies unless it is a large star.

Red Giant Stage If a star is large enough, the fusion of heavier elements occurs and the star becomes a giant and lives longer Some of the heat from the core is radiated outward which causes hydrogen fusion in the outer layers of the star. The additional energy causes the star to expand forming a giant. As the star expands, it’s surface cools causing the giant to become red.

Burnout and Death All stars regardless of size eventually run out of fuel and collapse due to gravity Low mass stars Never evolve into red giants Remain as stable main sequence stars until they consume all of their hydrogen and collapse forming a white dwarf

Medium mass stars Become red giants Once the fuel for fusion is gone, they collapse Once they collapse they cast off their outer layer which forms a cloud of gas The heat from the star causes the cloud to glow The glowing cloud is called a planetary nebulae The remainder of the star becomes a white dwarf

Massive Stars Become red super giants End in an explosion called a supernova The outer shell of the star is blasted away The result of the supernova is either a neutron star or black hole.

White Dwarfs The remains of low mass and medium mass stars Extremely small with very high densities White dwarfs can only evolve into a cooler and dimmer object Our sun will eventually become a white dwarf. Nebula → main sequence → red giant → planetary nebula → white dwarf → black dwarf

Neutron Stars Smaller than white dwarfs Thought to be the remnants of supernova events

Supernovae The outer layer of a star is ejected The core of the star collapses into a neutron star Neutron stars emit pulses of radio waves that line up with the magnetic poles of the star. This type of star is called a pulsar Pulsars are the remains of supernovae

Black holes Occur after a supernova event Have a gravity so strong that not even light can escape the surface

25.3 The Universe The Milky Way Galaxy Galaxies are large groups of stars, dust, and gases held together by gravity Our galaxy is the Milky Way. The Milky Way is a large spiral galaxy.

Structure of the Milky Way The Milky Way has at least 3 spiral arms The sun and solar system is positioned in one of the spiral arms The center of the Milky Way is called the galactic nucleus The stars in the arms of the Milky Way rotate around the galactic nucleus.

Types of Galaxies Spiral Disk shaped with a greater concentration of stars near the nuclei Arms extend from the center The Milky Way is a barred spiral galaxy in which the stars are arranged in the shape of a bar. Spiral arms attached to each bar

Elliptical Irregular Most galaxies Oval shape Irregular shapes Make up only about 10% of galaxies

Irregular galaxies are composed mostly of young stars Elliptical galaxies contain many old stars Spiral galaxies have both young and old stars with the youngest located in the arms

The Expanding Universe Most galaxies have a Doppler shift toward the red end which occurs when a light source is moving away from an observer. This means that most galaxies are moving away from us. The red shifts of distant galaxies indicate that the universe is expanding

The Big Bang Theory Not this one. Although I do like this one better and it does make more sense.

The Big Bang Theory According to this theory the universe began as a violent explosion from which the universe continues to expand, evolve, and cool. At one time the entire universe was confined to a dense, hot, supermassive ball. (singularity) It is believed that the big explosion happened about 13.7 billion years ago.

Evidence for the Big Bang Red shift Cosmic microwave background There are 2 theories for what will happen to our universe in the future It will continue to expand forever It will eventually collapse on itself and return to its original state