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Characteristics of StarsCharacteristics of Stars
• Groups of stars that form patterns in the sky are called constellations– Example: Ursa Major (Big Dipper), Ursa Minor (Little
Dipper), and Orion
• The last two stars in Ursa Major’s “dipper” can be used to find Polaris (North Star)
• Polaris is located directly above the North Pole (90º), and is only visible in the northern hemisphere
Circumpolar ConstellationsCircumpolar Constellations
• Because of the Earth’s rotation, the constellations appear to move
• If the constellations appear to move around Polaris, they are called circumpolar constellations – The constellations Ursa Major and Minor are both
circumpolar constellations • Using time exposure photography, the apparent
motion of the stars around Polaris can be recorded as circular trails
• The positions of the constellations as viewed from Earth changes from season to season
• This is caused by the change in Earth’s position in its orbit around the sun – Example: Orion the Hunter is a winter
constellation
Physical Properties of StarsPhysical Properties of Stars
• Stars differ in size, density, mass, composition, and color
• The color of a star is determined by it surface temperature (Reference Tables) – The hotter the star, the bluer the color. The
cooler the star, the redder the color. – The sun is a yellow star
• Most stars are made up of mostly hydrogen and helium (approx. 98%)
• The remaining 2% may be other elements • A spectrum analysis of the star can tell us what
elements a star is made of, since the radiated spectrum depends on a star’s composition and temperature
Physical Properties of StarsPhysical Properties of Stars
ApparentApparent MagnitudeMagnitude
• How bright a star appears on to us on Earth• The farther a star is from Earth, the dimmer it will
look even though it may actually be a very bright star– Because of this, apparent magnitude does not
tell the true brightness of a star
LuminosityLuminosity
• The actual (true) brightness of the star• Depends on the size and temperature of the star• Hotter stars are more luminous (brighter) than
cooler stars • If the temperatures are the same, a larger star will
be more luminous
Absolute MagnitudeAbsolute Magnitude
• The luminosity of the stars if they all were the same distance from Earth– aka – picture all the stars lined up the same
distance from Earth, then compare their brightness
• This is the most useful when comparing the brightness of the stars
Distances Distances to the to the StarsStars
• The sun is the closest star to Earth• It is approx. 150,000,000 km (93,000,000 miles) from the
Earth– This distance is called an astronomical unit (AU)
• The closest star to Earth, after the sun, is Alpha Centuri– It is 300,000 times farther away from Earth than the
sun. Because of the great distances in space, larger units of measure must be used
• The light-year is the distance that light travels in one year• Since light can travel 300,000 km/sec (186,000 miles/sec),
light travels 9.5 trillion km/year!!! – Alpha Centuri is 4.3 light-years from Earth!
Star Star FormationFormation
& & OriginOrigin
• large clouds of dust and gas in space are the basic materials needed for star formation
• the majority of this gas is hydrogen • some outside force causes the cloud to be
pushed together • as the gas and dust get closer, friction between
the particles causes the temperature to increase
• the attraction of gravity between the particles causes them to continue to move together, and density also increases
• friction increases and temperature increase until the center becomes so hot that nuclear fusion takes place
• hydrogen atoms are forced together to form helium atoms, and energy is released
• In a nuclear reactor like Indian Point, nuclear fission takes place – This is when radioactive atoms are split apart to
release energy
But where does the gas & dust But where does the gas & dust come from????come from????
SUPERNOVASSUPERNOVAS• One of the most energetic explosive events• occur at the end of a star's lifetime, when its nuclear
fuel is exhausted and it is no longer supported by the release of nuclear energy
• If the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energy
• This will cause a blast wave that ejects the star's envelope into interstellar space
Etna Carinae
Supernova ringsSupernova remnant
SUPERNOVA 1987 – right image is the star that became the left image after going supernova – shone brighter than most galaxies for a few months!
NEBULANEBULA
• Clouds of dust & gas (supernova remnants?)• 2 Main Types:
– Diffuse Nebula – nearby star illuminates the gas/dust cloud
– Dark Nebula – Dark patch against more-distant stars (dust/gas is blocking the light from stars behind it)
ORION NEBULA
KEYHOLE NEBULA
HELIX NEBULA
VEIL NEBULA
CAT’S EYE NEBULA
ESKIMO NEBULA
5000 LY FROM EARTH - 10,000 YRS OLD
CRAB NEBULA
A STAR IS BORN…A STAR IS BORN…
I WANT MY I WANT MY MOMMY!!MOMMY!!
THE BIRTH OF A STAR (OOH IT’S A GIRL!)
STELLAR NURSERY
A STAR BEGINS TO FORM IN A
NEBULA (CLOUD OF GAS & DUST)
GLOBULE
DUST & GAS COMPRESS DUE TO
GRAVITATIONAL FORCES, FORMING A SLOWLY ROTATING
GLOBULE
GLOBULE COLLAPSE
GRAVITY BECOMES TOO STRONG & THE
GLOBULE COLLAPSES,
SPINNING INCREASES
PROTOPLANETARY DISK & CORE
SPIN, PRESSURE, & TEMPERATURE
INCREASE, PLANETS ARE FORMED, AND CENTRAL
CORE (SUN) FORMED
LIFE CYCLE OF STARSLIFE CYCLE OF STARS
• A star’s life cycle is determined by its MASS– The larger the star, the faster it burns
out!• A star’s MASS is determined by the
MATTER available in the nebula of formation
LIFE CYCLE OF STARS
STELLAR NURSERY
STARS FORM IN A NEBULA
OF GAS & DUST
SUN-LIKE STARS(UP TO 1.5 X MASS
OF OUR SUN)
RED GIANT PLANETARY NEBULA
WHITE DWARF
BLACK DWARF
MASSIVE STARS
(1.5 – 3 X OUR SUN)
SUPERMASSIVE STARS
> 3 X OUR SUN
RED SUPERGIANT
RED SUPERGIANT
SUPERNOVA
SUPERNOVA
NEUTRON STAR
BLACKHOLE
DEATH OF A SUN-LIKE STAR
SUN-LIKE STAR RED GIANT PLANETARY NEBULA
WHITE DWARF BLACK DWARF
LONGEST, MOST STABLE PERIOD
OF A STAR’S LIFE – CONVERTS
HYDROGEN TO HELIUM,
RADIATING HEAT & LIGHT
NUCLEAR FUEL DEPLETES,
CORE CONTRACTS,
SHELL EXPANDS
OUTER LAYERS DRIFT OFF INTO
SPACE IN SPHERE-LIKE
PATTERN
STAR COOLS ARE SHRINKS
BECOMING ONLY A FEW THOUSAND
MILES ACROSS!
NO NUCLEAR REACTION
STAR LOSES ALL HEAT TO SPACE
AND BECOMES COLD AND
DARK
Handy Dandy Handy Dandy Earth Science Earth Science
Reference TablesReference TablesPage 15Page 15
H-R DIAGRAMH-R DIAGRAM
Properties of the SunProperties of the Sun • average size yellow star• fairly cool compared to other stars• diameter is approx. 110 times larger than
Earth’s, with a volume that hold more than 1,000,000 Earths.
• Light traveling from the sun takes approx. 8 minutes 20 seconds to reach Earth!
• surface temperature is approx. 5,500 C and its interior temperature is believed to be 15,000,000 C!!
Sunspots & ProminencesSunspots & Prominences
• Sunspots are regions of intense magnetic fields • Sunspot temperatures are cooler than the
photosphere, which makes them appear as dark spots
• Prominences are regions along a magnetic field line where conditions are right for light to be emitted
• Huge, arching columns of gas often appearing above sunspots
Solar FlaresSolar Flares
• Occasionally, kinks and stresses occur on magnetic field lines discharging amounts of energy (known as Solar Flares)
• The amount of energy released is equivalent to a 2 billion megaton bomb
• Flares release large numbers of particles into the corona
Source of the Sun’s EnergySource of the Sun’s Energy • The process of NUCLEAR FUSION• Einstein explained this process as
E = MC² (matter can be converted into energy)• The hydrogen molecules that the sun is made
of fuse together to form a helium atom. When this occurs, energy is given off!
• **It is estimated that the sun has enough mass for nuclear fusion to continue for 5 billion more years!
GIANTS/SUPERGIANTSGIANTS/SUPERGIANTS
• the brightest & largest kind of star • luminosities of 10,000 to 100,000 • radii of 20 to several hundred solar radii (about
the size of Jupiter's orbit)• two types are red supergiants (Betelgeuse and
Antares) and blue supergiants (Rigel)
Betelgeuse a red supergiant, with about 20 times the mass and 800 times the radius of the Sun, so
huge that it could easily contain the orbits of Mercury, Venus, Earth, and Mars. It will probably explode as a supernova at some point within the next 100,000 years. Even at its relatively remote distance, it normally ranks as the tenth brightest
star in the sky.
Rigel, a blue supergiant, has a diameter of about 100 million kilometers, some seventy times that of the Sun. Within a few million years, it will probably evolve to become a red supergiant like its neighbor in Orion (though not in physical space), Betelgeuse.
Dwarf StarsDwarf Stars• A term used, oddly enough, to describe any
star that is of normal size for its mass• The Sun, for example, is classified as a yellow
dwarf• In general, dwarf stars lie on the main
sequence and are in the process of converting hydrogen to helium by nuclear fusion in their cores
White DwarfsWhite Dwarfs
• A medium sized star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size
• Typically part of a planetary nebula• Eventually cools into a BLACK dwarf (lump of
carbon) – This takes BILLIONS of years!– This is the fate of OUR SUN!
Neutron StarNeutron Star
• The imploded core of a massive star produced by a supernova explosion
• The most dense known objects in the universe!– A sugar cube of neutron star material
weighs 100 million tons! (think Mt. Everest)
BLACKHOLESBLACKHOLES
• A supermassive star that undergoes supernova and the core of the star is “swallowed” by its own gravity
• readily attracts any matter and energy that comes near it
Blackholes cont…Blackholes cont…
• It is an area where the escape velocity is greater than the speed of light.
• The more massive an object is, the faster you have to travel to escape its gravity.
• This is known as the escape velocity. • Black holes are so massive that their escape
velocity is faster than the speed of light. • Since nothing can travel faster than light, nothing
can escape the gravity of a black hole.
3,700 LY wide dust-disk encircling a 300 million solar mass blackhole in the center of an elliptical galaxy.
The disk is a remnant of an ancient galaxy collision and could be “swallowed” up by the blackhole in a few billion years.
Galaxies & the Galaxies & the UniverseUniverse
GalaxiesGalaxies• system containing millions to billions of stars
– Ex. the Milky Way galaxy contains over 100 billion stars
• Milky Way galaxy is a spiral shaped galaxy with a large central cluster of stars, and thinner “arms” radiating out from the center – The solar system is located on one of the
arms of the Milky Way galaxy
Origin of the Milky WayOrigin of the Milky Way
• Formed 10-12 billion years ago• Possibly collided with smaller galaxies• Globular star clusters formed• Stars and solar systems formed roughly 5
billions years ago
Milky Way
Andromeda Galaxy – 2.9 million LY from earth
Sombrero Galaxy – 50 million LY from earth – 100,000 LY across
Hoag’s Galaxy – 120,000 LY wide – perfect ring of blue stars surrounding older nucleus of yellow stars
When galaxies collide…
Galaxy FormationGalaxy Formation• The formation of all the galaxies is explained by
the Big Bang Theory• Simply put, it states that the universe was a big
ball of hydrogen gas that exploded outward • The expanding cloud had areas that condensed
into galaxies that are still expanding out from the center (the universe is getting larger)– We can see this with RED SHIFT!
Space is BIG. Really BIG. You just won’t Space is BIG. Really BIG. You just won’t believe how vastly hugely mind-bogglingly believe how vastly hugely mind-bogglingly big it is.big it is.
