Science 6 Chapter 10 Stars Part 1

Characteristics of a Star

1) Brightness 2) colors of stars 3) size and distance of stars

Kinds of Stars

1) Variable star a) pulsating variable star b) eclipsing variable star 2) Nova 3) Supernova 4) Neutron star A) pulsar 5) Black Hole

Size of stars from smallest to largest

1) dwarf stars 2) giant stars 3) supergiants

Brightness

1) magnitude -- brightness of a star 2) apparent magnitude -- apparent brightness (how it looks to us) 3) absolute magnitude -- true brightness of a star

Sun has a diameter of

1,400,000 km

The sun is one of billions of stars in the sky The star nearest earth (the sun) is about _______ away, it is so near to us scientists can study it

150,000,000 km or 93,000,000 miles

Pulsar

A neutron star that spins rapidly on its axis - if a neutron stars core continues to collapse, it starts to spin rapidly and fling pulses of energy into space - this is how pulsars got their name and how astronomers find them - they trace the pulses of energy back to the star emitting (doing) them

Black hole

Astronomers believe that when a massive supergiant star runs out of fuel, it's gravitational force is so great that the core cannot stop collapsing - it essentially disappears from space.

Neutron star

Astronomers believe when some supergiants collapse the pressure in the core crushes the protons and electrons together to form neutrons - the core is made up of mostly neutrons - so a neutron star began as a supergiant hundreds of millions of kilometers may become as small as a few kilometers in diameter - the neutrons are very tightly packed in the neutron star

Proxima Centauri is the closest star to Earth

False/Sun is the closest star to Earth

The apparent movement or change in position of one star in relationship to other stars is know as pulsating

False/parallax

Stars are glowing balls of gases that reflect light

False/produce

The gravitational force of a black hole is so great that is pulls everything into it even

Light.

On February 19,1992, astronomers were excited to observe

Nova Cygni 1992. -- the brightest nova in recent history and could be seen with a telescope

Supernovas occur less than

Once a century in our galaxy - the last supernova in our galaxy occurred in 1604 some that occur in other galaxies can be seen from Earth with telescopes

Astronomers cannot see a black hole but they have seen the effects of the gravitational pull on other matter.

Sometimes when two stars are near each other gases from one star appear to spiral into a black hole - the light from the gases seem to just disappear

The relationship between a star's surface temperature and its color

Stars appear white but they are many colors. They are closely related to their surface temperature. The coolest stars are a dull red, and the hottest stars are blue --- Surface temp is hotter -- they are blue or brighter Cooler --- they are red or dimmer

The ___ is the closest star

Sun

Supernovas sometimes can be seen during

The day - after brightening the star fades and collapses - this explosion usually results in the complete destruction of the star and the remnants often become a neutron star or black hole

Supernova

The death explosion of a star.

Why are black holes not visible?

The gravitational force is so great that it pulls everything into it - even light

Astronomers believe that a supernova occurs when a massive star has used up its hydrogen fuel.

The star starts to collapse but the great pressure created by the stars gravity causes the star to to heat up quickly and explode. It increases in size and brightness and can become brighter than a galaxy

A light year is the distance that light travels in one year

True

A supergiant star that collapses and disappears from space is called a black hole

True

Variable stars regularly or repeatedly change in magnitude

True

Super giant star that would span all the way to Jupiter's orbit it if were place where the sun is

VV Cephei

What do we call stars that regularly or repeatedly change in brightness?

Variable stars

What usually causes a nova?

When an existing star suddenly flare up and becomes hundreds or thousands of times brighter than normal - because one stars gravity pulls gases from the other star

Hipparchus

a Greek who lived 130 years before the time of Christ, he devised the system still used today to classify stars by their brightness. He classified stars he could see as +1 on his scale. He classified the faintest stars as +6. Now telescopes can see much farther into space. Astronomers have adjusted Hipparchus scale. They have added negative numbers to represent objects that are even brighter than many stars. With huge telescopes they can see stars as faint as magnitude of +29 or greater.

Nebula

a cloud of interstellar gases and debris -- can be seen either because they glow from light within or because they block light from behind them and look like dark clouds

magnitude that indicates how bright a star really is

absolute

true brightness of a star

absolute magnitude

magnitude that indicates how bright a star appears to us

apparent

Describe the difference between apparent and absolute magnitude

apparent -- how bright a star appears to us (by looking in the sky) absolute --- the measurement of the true brightness of a star (special measurements are used to find this)

how bright a star appears to us

apparent magnitude

supergiants

are hundreds of times larger than the sun and thousands of times brighter

giant stars

are tens to hundreds of times larger and hundreds of times more luminous than the sun

light year

astronomers solve the problem of measuring in enormous numbers by using other units of measurement (light-year) --- the distance that light travels in one year

Astronomers can determine how far away from Earth some stars are by measuring how far stars appear to move compared to even more distant stars. To determine the distance a star appears to move,

astronomers take pictures of the star at 6 month intervals. These pictures enable them to view the star from opposite points in Earth's orbit around the sun.

apparent magnitude

astronomers use a set of numbers to represent apparent magnitude. Lower numbers represent brighter stars

The scientific study of the stars is called _____

astronomy

A ____ was once a supergiant star that collapsed and disappeared from space

black hole

Hottest Stars

blue

What color is the star with the hottest surface temperature?

blue

color of the hottest stars

blue

A ____ is a group of stars that form a picture in space

constellations

A light-year is the _____ that light travels in one year

distance

eclipsing variable stars

does not change its absolute magnitude but does change its apparent magnitude. -- pairs of stars that orbit each other because of their gravitational pulls on one another. -- the apparent brightness of the stars is greater when both stars can be seen. -- when one star eclipses, or moves between the earth and the other star, the reduction in light cause the apparent brightness to dim

Coolest Stars

dull red

kind of star that our sun is

dwarf

A star that is close to Earth will appear to move more than a star that is

far away. Scientists examine the photographs, noting a star's change in position in relationship to more distant stars.

Nova (means "new" in Latin)

forms when an existing star suddenly flares up and becomes hundreds or thousands of times brighter than normal. Even with a telescope people only spot about two to three novas in our galaxy each year.

day of Creation on which God created the sun, moon, and stars

fourth

kind of star that is hundreds of times brighter than the sun

giant

The sun is a

glowing ball of gases made up of about 70% hydrogen 28% helium 2% other elements

pulsating variable star

go through periods of swelling and brightening, then shrinking and dimming. The absolute magnitude of the star changes during this cycle. --- some change in regular patterns others seem to have no pattern at all

The inside of a star is so hot that hydrogen atoms fuse together to form

helium atoms --- as this fusion occurs, the star releases energy in the form of heat and light

the neutrons are very tightly packed in the neutron star

just one teaspoon of the stars core might weigh one billion tons

Name one unit of measurement scientists use for distances

light-year

how far light travels in one year

light-year

The _____ of a star depends on the star's size, temperature and distance from Earth.

magnitude

the brightness of stars

magnitude

absolute magnitude

measures how bright a star really is, not just how bright it appears to be. Astronomers determine absolute magnitude by imagining that all stars are the same distance from Earth. How bright a star would appear at that distance is the star's absolute magnitude. Special measurements and mathematics help astronomers calculate the absolute magnitude of a star

The sun is a

medium-sized yellow star

A cloud of dust, gases, and debris in space is called a

nebula

a cloud of dust, gases, and debris

nebula

may occur when a supergiant collapses to a very dense core

neutron star

A star that suddenly flares and becomes brighter is called a

nova

an existing star flares and becomes brighter

nova

Planets and moons only reflect light -- the sun and other stars produce their own light by

nuclear fusion

neutron star that spins rapidly on its axis

pulsar

The difference between pulsating variable stars and eclipsing variable stars

pulsating variable stars --- stars that go through periods of swelling and brightening, then shrinking and dimming -- the absolute magnitude of the star changes during this cycle and some change in regular patterns and some have no pattern at all. eclipsing variable stars -- does not change its absolute magnitude but does change its apparent magnitude. pairs of stars that orbit each other because of their gravitational pulls on one another. The apparent brightness of the stars is greater when both stars can be seen.

color of the coolest stars

red

dwarf stars

small and medium sized stars

When a star goes "nova" it

spews dust and gases into space. Its outer layers gradually float off into space, usually leaving a smaller, dimmer star behind

Size and Distance of stars

stars come in many sizes

Variable stars

stars that regularly or repeatedly change in magnitude

star closest to the earth

sun

kind of star that is hundreds of times larger than the sun and thousands of times brighter

supergiant

the death explosion of a star

supernova

parallax

the apparent movement or change in position of one star in relationship to other stars

magnitude

the brightness of a star depends on the stars Size, temperature, and distance from Earth

Proxima Centauri

the next closest star to Earth --- 270,000 times farther away from Earth than the sun --- 4.2 light years away

In AD 1054 Chinese astronomers saw a supernova

the remnants formed Crab Nebula The closet nebula to earth caused by a supernova

Colors of stars

when you first look at a star they appear white -- stars are actually many colors. a star's color is closely related to its surface temperature.