Astrophysics Flashcards by Naomi Barnor

What is the universe

A large collection of billions of galaxies

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What is the galaxy

A large collection of billions of stars

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what is our sun

juts on of the stars which form the Milky way galaxy

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The force due to gravity depends on which two key factors

mass
Radius/ distance

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what effect does distance and mass have on the gravity

The larger the mass of the body, the stronger it’s gravitational field strength

The shorter the distnace ( closer you are ) the stronger the gravitational field strength

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what does gravitational force do

Causes the moon to orbit planets
causes planets to orbit the sun
Causes artificial satellites to orbit the earth
Causes comets to orbit the sun

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Explain how gravitational force keeps an object in orbit

The gravitational force acts towards the body the object is orbiting

-This changes the direction of the velocity

This means the object is constantly changing direction without changing speed and moves in a curved path around the larger objects.

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What are the orbits of the moon and planets usually like

Slightly elliptical

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What type of orbit does a comet have

Very elliptical
orbits the sun at one focus

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How do you calculate orbital speed

Orbital speed= 2 x PI x orbital radius/ Time period

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How do you calculate the distnace of a circular orbit

calculate the circumference
= 2 x pi x orbital radius

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what do u measure distnace in

Metres

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What are the stages of stella evolution (summarised)

Nebula
Protostar
Main sequence
Red giant
- white dwarf
Red Super giant
- Supernova
- Neutron star
- Black hole

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What is Nebula

A cloud of dust and gas

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How does a star initially start of

from a cloud of stars and gas which is know as neubula

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What is a protostar and how is it formed

A protostar is the next stage in the life cycle of a star it follows after nebula

How is it formed?
- Force of gravity pulls together a cloud of dust an gas ( nebula) to form a protostar

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How is a star born

hint: formation of protostar

Temperature rises as stars get denser
particles have more kinetic energy
There are more collisions
When temperatures get high enough hydrogen nuclei under goes nuclear fusion to form helium nucleus
Gives off huge amounts of energy
energy given off keeps the core of the star hot
A star is born

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What is the next stage after a protostar is formed?

Main sequence

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Describe the main sequence?

A long stable period

outward pressure caused by thermal expansion balances the force of gravity pulling everything inwards
this stable period is called main sequence

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How long does a star stay in the main sequence

where is the sun now

Several Billions of years

The sun is in the main sequence

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What causes outward pressure in the main sequnece

Thermal expansion
this occurs from the huge amount of energy released from nuclear fusion TRYING to expand the star

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What comes after the main sequence

Red Giant
Red super Giant

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what size is the Red Giant

Same size as the sun

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What size is the RED SUPER giant

much bigger than the sun

What is the process of the Red giant

Hydrogen in the core begins to run out - force due to gravity is larger than the pressure of thermal expansion Star is compressed until dense and hot enough that the energy created makes the outer layers of the star expand

Why does it turn red after the main sequence

Because the surface cools

If it is a small or large star what will it become after the main sequence

Large- Red SUPER giant Small- Red giant

What follows after the red giant phase

The star is the same size as the sun so becomes a white dwarf

Describe the process of becoming a white Dwarf

A small- to medium sized star like the sun - becomes unstable and ejects it's outer layer of dust and gas. - leaving behind a hot dense solid core- white dwarf

What is a white dwarf describe as

Hot, dense solid core

What does a Red SUPER Giant become

Supernova

Describe the process a Supernova

- They expand and contract several times as the balance shifts between gravity and thermal expansion - eventually explode in a super nova

What is the stage after the Supernova

Neutron star or black hole

Describe the process of the forming of a neutron star

- Exploding supernova throws the outer layers of dust and gas into space - this leaves a dense core called a neutron star.

What forms a black hole

If the star is massive enough it will collapse and become a black hole

What is a black hole

A super dense point in space that not even light can escape from.

How can stars be classified

by their colours

What does the colour of a star depend on

Visible light it emits

What effects the amount of visible light a star emits of each frequency

Surface temperature

Rank the colour of stars from hot to cold

Hottest 1.Blue 2. White 3.Yellow 4.Orange 5. Red Coldest

What factors effect the stars Brightness

Size Temperature

If a star is really hot and big how bright will it be

Very Bright

Finish the sentence The closer the star .....

The brighter it appears

What do we use Absolute magnitude for

Classifying the brightness of a star Allows us to compare the brightness of stars without worrying about their relative distances from earth.

Which measurement of absolute magnitude is brighter - Positive or Negative

- Negative measurement is brighter than a positive measurement

What is the location of : - main sequence - Red giant/super giant - White dwarf on a HR diagram

- Main sequence= Middle - Red giant/super giant= Top right - White dwarf= Bottom left

What does a longer wavelength and lower frequency mean

Star is moving way from earth

what is redshift

The light from distance stars The amount of light from a galaxy

What equation is used to calculate redshift

Change in wavelength/reference wavelength = Velocity of a galaxy / speed of light

What does red shift Suggest

The universe is expanding

What does the expansion of our universe suggest

That something must have got them going that something causing their initial movement apart is the big bang theory

what are two evidence of the big bang theory

Cosmic microwave background radiation Redshift

How is CMB an example of evidence for the big bang theory

Appears to be the same in everywhere

what factors effect a stars brightness

size temperature distance bigger and hotter the star the brighter it is

The closer the star is to earth .....

the brighter it appears

What is absolute magnitude

The brightness of a star at a standard distnace

How do you analyse Redshift

The further away a galaxy is the greater the redshift The Greater the Redshift, the faster the galaxy is moving away As distnace increases, speed increases This implies expansion from a single point

What does cosmic radiation Proove

That all parts of the universe were in contact at one point