Stars

Studying Stars

• Astronomers use a spectroscope to study

the movement of stars

• Blue shift – towards earth

• Red shift – away from earth

• Change in a wavelength moving toward or

away from earth is the Doppler Effect

Galaxies Galore

• Types of Galaxies:

– Spiral – spinning wit “arms”

– Elliptical – roundish

– Irregular – no set pattern

• Star Clusters

– Open - apart

– Globular - together

What is a star?

• The objects that produces heat and

light in solar systems

• A star is a ball of plasma held

together by its own gravity

– Nuclear reactions occur in stars (H

He)

– Energy from the nuclear reactions is

released as electromagnetic radiation

Characteristics of Stars

• DISTANCE

– Measured in light-years

• The distance which a ray of light would

travel in one year

• About 6,000,000,000,000 (6 trillion) miles

• 186,000 miles per second

Characteristics of Stars

• Magnitude (brightness)

– A measure of brightness of celestial

objects

• Smaller values represent brighter objects

– Apparent magnitude

• How bright a star appears to be from Earth

– Absolute magnitude (luminosity)

• How bright a star actually is

Characteristics of Stars

http://www.seasky.org/cosmic/sky7a01.html

• Temperature & Color

– The color of a star indicates the Temp of

the star

– Stars are classified by Temp

• Decreasing Temp (bright to dim)

• O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss

Me ]

Hertzsprung-Russell Diagram

http://www.dustbunny.com/afk/stars/lifecycle/hrdiagram.gif

Main Sequence Stars

• A major grouping of stars that forms a

narrow band from the upper left to the

lower right when plotted according to

luminosity and surface temperature on the

Hertzsprung-Russell diagram

Types of Stars

Classification

Class Temperature Color

O 20,000- 60,000 K Blue

B 10,000 – 30,000 K Blue-white

A 7,500 – 10,000 K White

F 6,000 – 7,500 K Yellow-white

G 5,000 – 6,000 K Yellow

K 3,500 – 5,000 K Orange

M 2,000 – 3,500 K Red

http://www.answers.com/topic/stellar-classification

Life Cycle of Stars

http://hea-www.cfa.harvard.edu/CHAMP/EDUCATION/PUBLIC/ICONS/life_cycles.jpg

Life Cycle of Stars

• Begin their lives as clouds of dust and gas called nebulae

• Gravity may cause the nebula to contract

• Matter in the gas cloud will begin to condense into a dense region called a protostar

• The protostar continues to condense, it heats up. Eventually, it reaches a critical mass and nuclear fusion begins.

• Begins the main sequence phase of the star

• Most of its life is n this phase

Life Cycle of Stars

Life span of a star depends on its size.

– Very large, massive stars burn their fuel much faster than smaller stars

– Their main sequence may last only a few hundred thousand years

– Smaller stars will live on for billions of years because they burn their fuel much more slowly

• Eventually, the star's fuel will begin to run out.

Life Cycle of Stars

• It will expand into what is known as a red

giant

• Massive stars will become red supergiants

• This phase will last until the star exhausts

its remaining fuel

• At this point the star will collapse

Life Cycle of Stars

• Most average stars will blow away their

outer atmospheres to form a planetary

nebula

• Their cores will remain behind and burn as

a white dwarf until they cool down

• What will be left is a dark ball of matter

known as a black dwarf

Life Cycle of Stars

• If the star is massive enough, the collapse

will trigger a violent explosion known as a

supernova

• If the remaining mass of the star is about

1.4 times that of our Sun, the core is

unable to support itself and it will collapse

further to become a neutron star

Life Cycle of Stars

• The matter inside the star will be

compressed so tightly that its atoms are

compacted into a dense shell of neutrons.

If the remaining mass of the star is more

than about three times that of the Sun, it

will collapse so completely that it will

literally disappear from the universe. What

is left behind is an intense region of gravity

called a black hole

Life Cycle of Stars

http://www.seasky.org/cosmic/sky7a01.html