Stars and Galaxies Galaxies

sStarsThe SunEvolution of StarsGalaxies and expanding Universe

StarsConstellations are grouping together of stars by first Greeks/ Romans

They imagined constellations represented mythological characters, animals or objects

Stars in constellations are not necessarily clustered close together

88 constellations known today

Circumpolar ConstellationsEarth rotates on its axisWhen looking at the sky, the sky revolves around a center point called the North Star (located near the handle of the Little Dipper)

Constellations move around the North Star appearing during parts of the year and disappearing below the horizon during other times of year.

Some constellations appear year round that are near the North Star

rAbsolute and Apparent Magnitude[hianu49076b o[q9430Some stars can appear very bright but are actually are dim

stars very close to earth.Some stars appear dim but are very bright stars but are a great distance from earth

Absolute Magnitude: Actual amount of light given off by a star

Apparent Magnitude: is a measure of the light received on earth

Sirius is the brightest star , but is a dim star that is 100 times closer than Rigel (a star that is farther away). If both the same distance from earth Rigel would be so much brighter

Measurement in Space

To find distance to stars, astronomers use Parallax measurements

Using angles from earth on its revolution around the sun, they can calculate distances to stars

Measurement in Space• Units of distance of vast space is recorded in light years. It is

the distance light travels in one year (about 6 trillions miles in one year)

Properties of Stars

• Color of Star indicates its temperature• Red stars are relatively cool stars• Blue/white stars are relative hot stars• Yellow stars have medium temperatures•When light passes through a prism, the

light is divided into its spectroscope ranging from red, orange, yellow, green blue, indigo and violet.

Spectroscope•When light passes through a prism, the light

is divided into its spectroscope ranging from red, orange, yellow, green blue, indigo and violet. (red is cooler, blue/violet is hottest)• Star light is divided into its colors.• As the light passes through the stars

atmosphere, there are black lines in spectrograph caused by star’s atmosphere absorbing some of its radiation depending on the kinds of atoms in its atmosphere

Spectroscope

• Scientists knows the kind of black lines associated with elements in the atmosphere and can determine what the composition of the stars atmosphere is by looking at those dark lines

Spectrograph of a star

The Sun

• Sun is our closet star made up of layers of an atmosphere

• Energy is transfer to us through radiation and convection

Sun’s Atmosphere

• Photosphere: lowest layer. Temp is about 6000°K, known as its surface, but is not smooth• Chromosphere extends 1200 miles above

photosphere. Extends through a transition zone up to 6000 miles above surface• Corona is largest layer extends millions of miles

outward. Temperatures here is as high as 2 million degrees Kelvin• Charged particles are emitted though corona

and move through space as solar wind

Sun’s Layers

Surface Features

• Sun spots: dark areas that are cooler• Sunspots rotate as does the sun and can

follow the spots• Rotates faster at equator, slower at poles• Sunspots cycle every 10-11 years• Prominences and Flares• Intense magnetic fields associated with

sunspots might cause prominences (huge arching columns of gas)

Surface Features

• Solar Flares: violent eruptions of gas near sunspots shoot outward at great speeds• CME’s are coronal mass ejections of

electrical charged gasses• Can damage earths satellites, interfere

with radio and power distribution equipment…. Produces auroras in northern hemisphere

Average Star: The Sun

• Middle aged, absolute magnitude is about average• Shines yellow light• Takes 8 minutes for light to reach earth• It is unusual in fact it is found as a single star

(normally stars are in groups of 2 (binary system)• Star clusters: group of stars that have a

gravitation attraction to each other• Appear fuzzy in sky. Pleiades star cluster is obvious

in winter skies .. Far from solar system

Evolution of Stars

Stars in the sky might appear similar, but are quite different

Hertzsprung and Russell observed characteristics where higher temperature stars also have brighter absolute magnitudes

Developed a graph that showed this relationship called the H-R diagram (Temperature along horizontal axis and brightness in the vertical axis)

H-R Diagram

Main Sequence Stars• Diagonal band that runs from upper left to lower right within

the H-R Diagram• This gives a continuous flow of how a star is born and how it

becomes older. A main sequence star moves through the band as it ages

• Upper left is hot bright stars, lower right is cool din stars• Our sun is in the middle indicating middle age star

• 90 % of all stars are a main sequence star• 10% of stars aren’t part of Main Sequence• Some are hot but dim (lower left called white dwarfs)• Some are bright and cool (upper right called giants)

Dwarfs and Giants

Generating Energy• Hydrogen fuses together to form Helium with great release

of energy.• It releases electromagnetic energy in the form of light,

infrared, and ultraviolet light. Tiny fraction of light reaches earth

• During fusion, 4 Hydrogen atoms fuse to form Helium where small amount of mass is lost to energy in reaction (large amount of energy is released)

• Fusion occurs in cores of all stars. In the core of stars the temperatures are high enough to fuse atoms

Evolution of Stars• As more and more H atoms are fused together, the fuel is

depleted• Stars evolve depending on its original size• Birth of Stars: begin as a large cloud of gas and dust called

nebula…. Gravity will pull gas and dust together which eventually causes an unstable condition. It breaks into smaller pieces that eventually become a new star

• Star is born when pieces move closer together, temperature increases. When Core reaches 10 million degrees K, fusion begins. Energy is released and star is born

Evolution of Star• When stars begin the fusion process, they follow the Main

Sequence stars path• When H is depleted, the balance between the gravity and

pressure no longer exists.• Core contracts, temperatures increase, outer core expands

and cools and forms a late stage life cycle called a giant

When temperatures reach 100 million degrees K, helium begins to fuse to form Carbon in giant’s core

The giant has expanded to an enormous size and its out layers are much cooler. Our Sun will be a giant in about 5 billion years

White Dwarfs

•When He is eventually used up, core contracts inward and out layers escape into space• Leaves behind hot, dense core• Our sun will become a white dwarf and

the sun at this stage is about size of Earth• It will finally cool and stop giving off light

Supergiants and Supernovas• If a star is 8 times more massive than out sun, the stages are

different• Cores heat up to much higher temps, heavier elements fuse

together and star expands to supergiant.• Eventually Fe forms in the core, and Fe can’t fuse to produce

energy• Core collapses violently and shock waves travel outwards• Outer portion of star explodes producing supernova• Neutron stars: if collapsed core of supernova is between 1.4

to 3 times as massive as the sun, it will shrink to about 12 miles in diameter and a neutron star forms• These are so dense that a teaspoon would weigh more than 600

million metric tons

Black Holes• If remaining core of supernova is more than 3 times more

massive as the sun, probably nothing can stop the core’s collapse. The core collapses to a point

• Gravity is so strong that nothing can escape from it, not even light

• When light can’t escape, it is called black hole• Black holes has an event horizon that if light enters it will

enter the black hole• If an object does not cross the event horizon it will not be

drawn into the hole, rather orbit around black hole

Recycling Matter• Star begins its life as a nebula, (parts of old stars that ejected

enormous amounts of matter during its lifetime)• Star cores created during supernovas produce larger atoms of

carbon and iron• These stars formed from supernovas and nebulas contain

heavier elements that could only have formed from recycled stars

• Our sun isn’t large enough to produce Fe in atmosphere, so the Fe had to have come from stars that died many Billions of years ago

• Some elements condense to form planets. Our bodies contain many atoms that were fused in the cores of ancient stars

• Are we are just recycled stars??????

Interactive H-R Diagram• http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html

Galaxies and the Universe

• Galaxies: large group of stars, gas and dust held together by gravity• Earth and our solar system belong to the

Milky Way Galaxy which is made of a trillion stars• It is found close to 45 other galaxies

known as the Local Group• These galaxies are separated by millions

of light years.

Types of Galaxies• Sprial Galaxies: spiral arms that wind outward from center• Milky Way is a spiral galaxy• Can be normal or barred

Galaxy types• Elliptical Galaxies: shaped like large 3 dimensional ellipse.

Looks like a football., some are round• Some of these galaxies are huge fitting several Milky Ways

into one

Irregular Galaxies• Galaxies that don’t fit into other two. Many different shapes

Milky Way Galaxy

• 100,000 light years across• Sun is located 2/3 way from the center• Takes 225 million years for sun to rotate around the

center• Classified as normal spiral galaxy (recent studies show

think it might be barred)• Milky Way is spread across the sky in a misty band• Black hole found in center (2.5 million times more

massive as the sun)

Origin of Universe

• Steady state: universe has always existed, new matter forms in center and expands outward

• Oscillating model: universe began to expand, then contracted and oscillated between expansion and contractions

• Big Bang Theory: universe began with a big bang and has expanded ever since

Expansion of the Universe

• Doppler Effect: a shift of wavelengths (sound or light waves) that reflect a change of pitch or change of spectrograph• As a train approaches you the wavelengths are

compressed and pitch is high, as it passes the wavelengths are expanded and pitch is lower• Light does same thing, rather a shift on the

spectrograph toward to red it is going away from earth, and if shifted to blue it is approaching earth

Doppler Shift

Big Bang Theory

• Occurred about 13.7 billion years ago• Entire universe began expanding at the same time• Hubble Telescope shows more than 1500 galaxies at

distances of more than 10 billion light years away.• These galaxies could date back to when universe was no

more than a 1 billion old and are in different states of developments• Will the universe expand and gravity will begin to

contract back to a single point• Whether the universe will continue to expands depend

on the dark energy that is causing the universe to expand faster