Stars & Constellati

onsAstronomy 2

What is a Star?

Star: A body of gas that gives off a tremendous amount of radiant energy in the form of light and heat

Stars close to home… The nearest star to Earth is

our Sun It takes approximately 8

minutes for the light from the sun to reach Earth

The next nearest star is called Proxima Centauri It takes approximately

4.2 years for the light to reach Earth (traveling at light speed)

The sun and Proxima Centuri are only two of the billions of stars in the Milky Way galaxy

What is Light?A form of A form of electromagnetic radiationelectromagnetic radiation

which is energy that travels in waveswhich is energy that travels in wavesElectromagnetic radiation is Electromagnetic radiation is

arranged in a continuum called the arranged in a continuum called the electromagnetic spectrumelectromagnetic spectrum

Light and the Universe

Light Year—used as a as a measurement of the great measurement of the great distances in spacedistances in space

A A light year is the distance is the distance that a ray of light can that a ray of light can travel in a year, or: travel in a year, or:

A light year is A light year is 5,865,696,000,000 5,865,696,000,000 milesmiles (9,460,800,000,000 (9,460,800,000,000 kilometers). kilometers).

A star or a star system’s A star or a star system’s distance from earth is distance from earth is measured in light years. measured in light years.

Parallax A change in an object’s direction

due to a change in the observer’s position.

Astronomers also use parallax to calculate the distance to the stars.

Parsec—short for “parallax second”—is a special unit of distance for a star’s distance from earth. > 1 parsec = 3.258 light years

Why Do Stars Twinkle??

The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation)

Stars (except for the Sun) appear as tiny dots in the sky

As their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions

This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling)

Characteristics of Stars

Size: anywhere from 20km to 1 trillion km in diameter

Mass: the amount of matter

Color: stars can be red, blue, white, orange or yellow

Composition: contain different elements determined using spectra

Characteristics of Stars

Temperature: Blue is the

hottest (35000°C)

Red is the coolest (3000°C)

Yellow (our sun) (5500°C)

Characteristics of Stars

Absolute MagnitudeAbsolute Magnitude—A—A measure of how bright a star measure of how bright a star would be if all Stars were at would be if all Stars were at the same distance—ten the same distance—ten parsecs—from Earthparsecs—from Earth

• Apparent MagnitudeApparent Magnitude—A —A measure of how bright a star measure of how bright a star appears to be on earthappears to be on earth• Does not measure how bright a Does not measure how bright a

star actually isstar actually is

Luminosity—the actual brightness of a star

Depends on size and temperature

The lower the number, higher The lower the number, higher the brightnessthe brightness

•

0-10-20-30 10 20 30

Magnitudes

Dimmer

Brighter

Our Our SunSun

Sirius Sirius

Brightest in the sky from

Earth

Polaris/North Star

-26.5 -2 3 6

We can not see dimmer than +6 with naked eye

Star 1

High luminosity

Far from earth

= lower apparent

magnitude

Star 2

Low luminosity

Close to earth

= higher apparent

magnitude

Apparent Magnitude

v.

Luminosity

Hertzsprung-Russel Diagram

Relationship between the absolute magnitude (luminosity) and the temperature of stars.

Spectral Class—designates the color of stars >depends on temperature >Hottest to the coolest >Blue to White to yellow to orange to Red

Kinds of Stars

Super giants- largest of all stars, very luminous

Red giants- cooler, large, very luminous

Dwarf stars- less luminous, red, orange or yellow

White dwarf- very faint, small and dense

Variable Stars- vary in vary in brightness over regular brightness over regular periods or cyclesperiods or cycles

Kinds of Stars

2 types of variable 2 types of variable stars:stars: AA. . pulsatingpulsating change in change in

brightness as they brightness as they contract contract (brighter)expand (brighter)expand (dimmer)(dimmer)

PulsarsPulsars star that releases light and

radio waves in pulses may be the neutron star

formed in a supernova it looks like it pulses

because it is rotating, like a searchlight

Kinds of Stars

2 types of variable 2 types of variable stars:stars: B. non-pulsating

Eclipsing Binary 2 stars of unequal

brightness that revolve around each other

brightness depends on which one is in front of the other

Life Stages of Stars & Constellations

Astronomy 2Astronomy 2

NebulaeSeen only in infraredHuge clouds of dust (1%) & gas

(99%)This is where most stars are born.

Stellar nursery is a nebula ( a large cloud of hydrogen gas in space) in which star formation is occurring

Life Cycle of a Star A star begins it’s life in a cloud of

cold gas and tiny-grained dust called a NEBULA.

Parts of the Nebula begin to condense due to some outside force—a shockwave—which acts upon it.

Due to gravity, the gas and dust pockets continue to condense and their temperature increases.

Eventually, parts of the Nebula begins to glow—PROTOSTARS are formed.

Gravitational contraction of the Protostars continues causing them to become hotter and brighter.

Finally, fusion takes place in the center of a protostar, halting gravitational condensation, and a star is born.

Life Cycle of a Star Main Sequence Star Main Sequence Star

(Our Sun)(Our Sun)—— 90% of all stars90% of all stars The star is stableThe star is stable Burns Hydrogen gas to Burns Hydrogen gas to

Helium Helium in its core in its core through nuclear fusionthrough nuclear fusion

The energy released The energy released causes the star to causes the star to shine.shine.

Stars spend about 90% Stars spend about 90% of their active lifetime of their active lifetime as main sequence stars. as main sequence stars.

Life Cycle of a Star

Red GiantRed Giant—— The star begins to The star begins to

run out of fuel and run out of fuel and the core begins to the core begins to shrinkshrink

Helium turns into Helium turns into CarbonCarbon

Rapid burning of Rapid burning of helium causes outer helium causes outer layer to puff out, layer to puff out, cooling the starcooling the star

The star turns redThe star turns red

Life Cycle of a Star Planetary Nebula

Outer layers are ejected as core continues to shrink

Shell of hot gas Core is exposed

White Dwarf— Low mass core

continues to shrink creating a white dwarf

Surrounded by the Planetary Nebula

Stars Evolution

Hydrogen fuses more quickly Hydrogen fuses more quickly and when a star starts to die, and when a star starts to die, iron nuclei are formediron nuclei are formed

Star swells to 100 times Star swells to 100 times diameter of the diameter of the sun—Super Giant

Iron nuclei absorbs energy and Iron nuclei absorbs energy and core quickly and suddenly core quickly and suddenly collapsescollapses

If large enough it explodes into If large enough it explodes into a brilliant burst of a brilliant burst of light—Super Nova then

Either a neutron star forms - dense mass of neutronsdense mass of neutrons

Or a Black Hole (depending on the size) - a concentration of - a concentration of mass great enough that the mass great enough that the force of gravity will not allow force of gravity will not allow anything to escapeanything to escape

Novas & Supernovas Believed to only

happen in binary-stars systems.

Gases from one star hit the surface of another and cause a nuclear type explosion.

Supernova is a brilliant burst of light that follows the collapse of the iron core of a massive star.

Super Nova

Quasars Quasars: give off radio & X-

waves. They are the most distant objects in space. Give off tremendous amounts of energy.

Quasars give off enormous amounts of energy - they can be a trillion times brighter than the Sun!

Quasars are believed to produce their energy from massive black holes in the center of the galaxies in which the quasars are located. Because quasars are so bright, they drown out the light from all the other stars in the same galaxy.

Where did the Constellations come from?

Farmers invented the constellations

It is known that crops are planted in the spring and harvest in the fall. But in some regions, there is not much differentiation between the seasons

Since different constellations are visible at different times of the year, you can use them to tell what month it is.

For example, Scorpius is only visible in the northern hemisphere's evening sky in the summer.

Where did the Constellations come from?

Some historians suspect that many of the myths associated with the constellations were invented to help the farmers remember them - when they saw certain constellations, they would know it was time to begin the planting or the reaping

Looking at the Constellations

Constellations are not real – they are only as a way to remember where stars are in the sky

Constellations are a group of stars that appears to form a pattern as seen from Earth.

The constellations help by breaking up the sky into more manageable bits

Example: if you spot three bright stars in a row in the winter evening, that's part of Orion – the star Betelgeuse is Orion's left shoulder and Rigel is his foot

Looking at the Constellations

Constellations There are 88

constellations or sky divisions

The constellations change position with each season

Some constellations only come up during certain seasons, some not at all

Some never change position due to their position to the poles—circumpolar Constellation of Orion

is seen during winter

Constellations Polaris (North Star) Found at the end of the

handle of the Little Dipper (asterism)-which makes up the constellation Ursa Minor (Little Bear)

Also can be found for using the pointer stars in the Big Dipper (asterism)-which makes up the constellation Ursa Major (Big Bear)

Also used for navigational purposes

The Constellation, Orion