Download Stars and Sun

STARS
Amy Johnson
In General
Stars are always in the sky, but can only be
seen at night when the atmosphere is not so
bright
The Sun is the closet star to Earth.
Stars appear to move across the sky at night
due to the rotation of Earth on its axis.
Star patterns in the night sky change
seasonally due to its revolution.
Constellations
A group of stars that form patterns in
the sky
Most visible
• Ursa Major-Big Dipper
• Ursa Minor-Little Dipper
Starry Colors and Size
Color gives clue to the temperature of
the star
Red is the coolest of the visible stars
Yellow stars are medium temperature
Bluish-white are the hottest stars
Most stars are small
Sun is a medium star
Betelgeuse – would swallow the first four planets
Apparent Magnitude
A system used in classifying the brightness of
a star from Earth
The smaller the number, the brighter the star
Sirius, the brightest star, measures a -1.5
Sun measures a –26.7
The sun looks brighter due to its location to
Earth
The Life of a Star - Birth
Begin as gas and dust
Gravity causes dust and gas to move
close together
Temperatures rise and cause atoms in
cloud to merge
Process called fusion and changes
matter to the energy that powers the
star
The Life of a Star - Evolving
Small and medium stars use up the
gases in the core and become a giant
star
Large, cool stars, red in color
Sun will become a giant in 5 billion years
• Will cover orbit of Mercury, Venus and Earth
• Will be a giant for a billion years
Evolving
Large stars become supergiants
Core collapses, shock wave, explosion,
becomes brighter
• Explosion known as a supernova
• Might shine more brightly than entire galaxy
• Released dust and gas may become part of a
new star
If core remains, it becomes a neutron star
If core collapses rapidly, a black hole forms
The Life of a Star - Death
The outer shell of the star will be lost
The core shrinks and is known as a
white dwarf
White dwarfs are hot and small
Eventually, white dwarfs cool and stop
shining – black dwarf
Galaxies
A group of stars, gas, and dust held
together by gravity
Elliptical
Very common, football shaped
Spiral
Giant pinwheel, some with bar-shaped
Irregular
Common, smaller, not easily classified
Galaxy contents
Nebulas- clouds of gas
Globular clusters- groups of old stars
Open clusters- stars on the spiral disk,
newly formed blue stars
Milky Way
Giant, spiral galaxy
Contains hundreds of billions stars,
including the Sun
Stars revolve around the center of
galaxies
once every 225 million years the Sun
makes a revolution
What We See
Only part of the Milky Way is visible due
to our being in the galaxy
Galileo saw the Milky Way in 1609 using
a telescope
Bigger and brighter than most galaxies in
the universe
Special stars
Supernova - an exploding star
Neutron star- remainder of supernova
Pulsars-spinning neutron star
Quasars- galaxies in the process of
forming, incredibly bright
Black hole- beyond pulsar that does not
allow anything to escape
Speed of Light
Light travels through space 300,000 km/s
Around Earth 7 times in one second
You cannot go faster than light
Light-years measures distances between
galaxies since the distance is so vast
The distance light travels in one year = light year
(9.5 trillion km)
Universe
Galaxies contain billions of stars
Billions of galaxies make up a universe
In 1995, the Hubble Space Telescope
discovered over 1,500 galaxies in a tiny
sector of the sky