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Physics (Elliott) > Mapping the universe > Flashcards

Flashcards in Mapping the universe Deck (39):
1

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

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.

2

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

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

3

Evidence for space expanding has come from what?

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

4

what is parallax?

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.

5

How do you define a Parallax angle?

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.

6

The effect of parallax can be used to measure what?

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.

7

What is a parsec?

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.

8

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

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

9

Each degree has how many minutes in it ?

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

10

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

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

11

1 second of an arc is what size of angle?

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).

12

Is a parsec is a similar distance to what?

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).

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.

The Sun is the nearest star to Earth.

14

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

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

15

Astronomers measure great distances in megaparsecs (Mpc).

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

16

The next nearest galaxy is ?, .

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.

17

How far away is Andromeda?

0.77 Mpc away. This is 770,000 pc.

18

What is the parallax angle of the andromeda galaxy ?

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

19

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

its size
its temperature

20

What are Cepheid variable stars ?

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).

21

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

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.

22

What is the Big Bang theory ?

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

23

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

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.

24

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

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.

25

What is ‘red shift’.?.

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’.

26

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



Speed of recession (km/s)
= Hubble constant (km s-1 Mpc-1) x distance (Mpc)

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.

distance = speed of recesson /Hubble constant

28

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

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

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.

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.

30

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

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.

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.

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.

32

What is peak frequency?

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.

33

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

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 -

34

What colour is emission spectrum of hydrogen?

Red

35

What is the simplest emission spectrum?

hydrogen

36

Is infrared low or high frequency?

Low

37

What colour is high frequency?

ultraviolet.

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 ............ ........ ... .....

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

39

How do you calculate angular magnification ?

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