Mapping the universe

Question 1

Scientists believe that the universe was created in the ………. and this………… million years ago.

Answer 1

Scientists believe that the universe was created in the ‘Big Bang’ 14,000 million years ago. Since then, the galaxies in the universe have all been moving further apart as space itself expands. Evidence for this comes from observations that astronomers have made of stars.

Question 2

Since then, the galaxies in the universe have all been ….. ……….. apart as ……… ………… expands.

Answer 2

Since then, the galaxies in the universe have all been moving further apart as space itself expands.

Question 3

Evidence for space expanding has come from what?

Answer 3

Evidence for this comes from observations that astronomers have made of stars.

Question 4

what is parallax?

Answer 4

When the observer moves, objects that are closer appear to move relative to ones that are far away.

Parallax makes stars that are nearer to Earth appear to move over the course of a year, relative to stars that are further away. In fact, it is caused by the movement of the Earth around the sun.

Hold one finger up in front of you at arm’s length. Close one eye. Now open that eye and close the one that was open. Repeat this a few times. Your finger seems to move against the background, even though you know that it is actually staying still. That is called parallax.

Question 5

How do you define a Parallax angle?

Answer 5

The parallax angle of a star is defined as half the angle that a star moves in six months, against a background of very distant stars.

Question 6

The effect of parallax can be used to measure what?

Answer 6

The effect of parallax can be used to measure how far stars are from Earth. The smaller the parallax angle, the further away the star is.

Question 7

What is a parsec?

Answer 7

A parsec (pc) is a unit of distance that astronomers use. A parsec is defined as being the distance to a star with a parallax angle of 1 second of an arc.

Question 8

There are ? degrees in a circle. Each degree has ? minutes in it, and each minute has ? seconds in it.

Answer 8

There are 360 degrees in a circle. Each degree has 60 minutes in it, and each minute has 60 seconds in it.

Question 9

Each degree has how many minutes in it ?

Answer 9

Each degree has 60 minutes in it, and each minute has 60 seconds in it.

Question 10

How many seconds are there in one degree of a circle?

Answer 10

there are 3,600 seconds in just one degree of a circle.

Question 11

1 second of an arc is what size of angle?

Answer 11

This means that 1 second of an arc is a very small angle indeed, which means that a parsec is a very large distance - similar in size to one light year (the distance that light can travel through space in one year).

Question 12

Is a parsec is a similar distance to what?

Answer 12

This means that 1 second of an arc is a very small angle indeed, which means that a parsec is a very large distance - similar in size to one light year (the distance that light can travel through space in one year).

Question 13

which start is nearest to Earth.? The next closest star is Proxima Centauri. It has a parallax angle of 0.77 seconds of arc.

Answer 13

The Sun is the nearest star to Earth.

Question 14

Which star is second closest star ? What is its parallax angle?

Answer 14

The next closest star is Proxima Centauri. It has a parallax angle of 0.77 seconds of arc.

Question 15

Astronomers measure great distances in megaparsecs (Mpc).

Answer 15

Astronomers measure even greater distances, such as those between galaxies, in megaparsecs (Mpc).

Question 16

The next nearest galaxy is ?, .

Answer 16

The next nearest galaxy is Andromeda, which is 0.77 Mpc away. This is 770,000 pc. The parallax angle of the Andromeda galaxy would be too small to measure.

Question 17

How far away is Andromeda?

Answer 17

0.77 Mpc away. This is 770,000 pc.

Question 18

What is the parallax angle of the andromeda galaxy ?

Answer 18

The parallax angle of the a galaxy would be too small to measure

Question 19

The luminosity of a star depends on two things - what are they?

Answer 19

its size

its temperature

Question 20

What are Cepheid variable stars ?

Answer 20

Cepheid variable stars do not have a constant luminosity. They pulse light and their luminosity depends on the period of their pulses (how long each pulse lasts).

Question 21

How do astronomers to estimate the distance to Cepheid variable stars -

Answer 21

This relationship allows astronomers to estimate the distance to Cepheid variable stars - as long as they know how bright the star actually is and how bright the star appears to be.

Question 22

What is the Big Bang theory ?

Answer 22

Scientists believe that the universe began with a huge explosion called the Big Bang about 14,000 million years ago.

Question 23

Edwin Hubble by observing Cepheid variable stars in distant galaxies and concluded what?

Answer 23

Edwin Hubble made observations of Cepheid variable stars in distant galaxies and concluded that the universe is expanding. In fact, the further away a star is, the faster it is moving.

Question 24

How do scientists work out the value of the Hubble constant?

Answer 24

Because scientists knew how far away some Cepheid variable stars were (their distance) and were able to use the red shift from these stars to calculate the speed with which they were moving away from us (the recession speed), they were able to calculate a value of the Hubble constant.

Question 25

What is ‘red shift’.?.

Answer 25

Light that travels towards Earth from a star that is moving away from us is shifted towards the red end of the spectrum. This is known as ‘red shift’. The faster a star is moving away from us, the more its light is ‘red shifted’.

Question 26

What is the equation for the Speed of recession (km/s)?

Answer 26

Speed of recession (km/s)

= Hubble constant (km s-1 Mpc-1) x distance (Mpc)

Question 27

How do you rearrange the formula for the speed of recesson so that we can work out the distance to a galaxy if we know its speed of recession.

Answer 27

distance = speed of recesson /Hubble constant

Question 28

The speed of recession can often be deduced from the galaxy’s ??

Answer 28

The speed of recession can often be deduced from the galaxy’s red shift.

Question 29

How have scientists worked out more accurate values for the Hubble constant using data on the speed of recession and the distance of galaxies.

Answer 29

Similarly, scientists have rearranged the equation to work out more accurate values for the Hubble constant using data on the speed of recession and the distance of galaxies.

Question 30

What does studying the radiation emitted by stars, such as the Sun, helps us to understand ?

Answer 30

Studying the radiation emitted by stars, such as the Sun, helps us to understand the processes that occur when stars are formed, create new elements and eventually die. There are several types of star, depending on their age and mass. And there is some convincing evidence of ‘extrasolar’ planets that orbit hundreds of nearby stars, other than the Sun.

Question 31

What do all hot objects, including stars, emit ? a continuous range of radiation in the electromagnetic spectrum. The luminosity (brightness) and peak frequency of this radiation increases as the temperature of the object increases.

For example, an object that is red hot emits radiation in the red part of the visible spectrum. An object that is much hotter, such as the Sun, has a peak frequency which lies more centrally in the visible light range of electromagnetic radiation frequencies.

Absorption and emission spectra

When atoms in a pure element are excited (given lots of energy) they give off light at fixed and characteristic frequencies. These frequencies directly relate to the colour - from low frequency infrared, through the visible spectrum, and up to high frequency ultraviolet.

These emission line spectra are like a chemical fingerprint for that element. They are caused by the movement of electrons between energy levels in the atoms. Hydrogen has the simplest emission spectrum.

The emission spectrum of hydrogen (red).

A star will give off energy at a range of frequencies, but there will be some gaps in it. Here is the spectrum of light given off by the Sun.

Answer 31

All hot objects, including stars, emit a continuous range of radiation in the electromagnetic spectrum. The luminosity (brightness) and peak frequency of this radiation increases as the temperature of the object increases.

Question 32

What is peak frequency?

Answer 32

an object that is red hot emits radiation in the red part of the visible spectrum. An object that is much hotter, such as the Sun, has a peak frequency which lies more centrally in the visible light range of electromagnetic radiation frequencies.

Question 33

What do excited atoms do? (that you wouldn’t do?)

Answer 33

When atoms in a pure element are excited (given lots of energy) they give off light at fixed and characteristic frequencies. These frequencies directly relate to the colour -

Question 34

What colour is emission spectrum of hydrogen?

Answer 34

Red

Question 35

What is the simplest emission spectrum?

Answer 35

hydrogen

Question 36

Is infrared low or high frequency?

Answer 36

Low

Question 37

What colour is high frequency?

Answer 37

ultraviolet.

Question 38

Emission line spectra are like a chemical fingerprint for that element. They are caused by what? .

A star will give off energy at a range of ……………, but there will be ………… …….. … …..

Answer 38

A star will give off energy at a range of frequencies, but there will be some gaps in it.

Question 39

How do you calculate angular magnification ?

Answer 39

angular magnification = focal length of objective lens/focal length of eyepiece lens