Astronamy

Question 1

If you just observe the planets with your eyes, what does it seem like?

Answer 1

It seems that the sun (our star) and the planets are all orbiting the Earth

Question 2

Who made one of the best known early models of what he could see in the sky?

Answer 2

The Greek astronomer Ptolemy (c100-170). His idea put the earth in the centre of everything with the planets and the sun orbiting around it - a geocentric model

Question 3

What did the polish astronomer nicolaus Copernicus (1473-1543) think about ptolemy’s model?

Answer 3

He thought that ptolemy’s measurements fitted a different model - a heliocentric model with the sun at the centre of the solar system

Question 4

Describe the invention of the telescope

Answer 4

The invention of the telescope at the end of the 16th century allowed scientists to see objects in space in much greater detail and to find new objects. Using a telescope, the Italian astronomer Galileo Galilei (1564-1642) disobeyed four of Jupiter’s moons. By plotting their movements, he showed that not everything orbited the Earth. This and other observations led him to support Copernicus’s idea.

Question 5

As telescopes improved, what discoveries were made?

Answer 5

The planets Uranus and Neptune and the dwarf planet Pluto. Smaller rocky bodies called asteroids were also discovered, most of which are found between the orbits of Mars and Jupiter. Comets are mostly made of ice, and some can be seen with the naked eye but many more have been found using telescopes

Question 6

What does our current model of the solar system include?

Answer 6

It includes eight planets, five dwarf planets, thousands of comets and millions of asteroids. These all move in elliptical (squashed circle) orbits around the sun. Many of the planets also have natural satellites (moons) orbiting around them

Question 7

What did the invention of astronomy allow astronomers to make?

Answer 7

More detailed observations and measurements than was possible by making drawings.

Question 8

What have computers increased the speed and detail of?

Answer 8

Computers have further increased the speed and detail with which information from telescopes can be analysed

Question 9

Photography enables astronomers to make detailed observations, what are computers used for?

Answer 9

Analysis

Question 10

Telescopes in orbit around the earth give much clearer images than ground-based telescopes why?

Answer 10

Because clouds and dust in the air do not interfere with the the image

Question 11

What do we use to investigate the solar system?

Answer 11

Space probes

Question 12

Many objects in space emit radio waves and infrared radiation. Different types of telescope are used to detect different types of electromagnetic waves. Why must some of these telescopes be placed in orbit?

Answer 12

Because the atmosphere absorb some of the radiation they are designed to detect

Question 13

What is weight?

Answer 13

You weight is the force of gravity acting on you

Question 14

What does your weight depend on?

Answer 14

Your weight depends on you mass and the gravitational field strength (g) of the earth

Question 15

What is gravitational the field strength on earth?

Answer 15

9.81N/kg

Question 16

What does the gravitational field strength on the surface of a body (such as a planet or the moon) depend on?

Answer 16

Depends on the mass of the body and the distance from its centre to its surface (it’s radius). The greater its mass and the smaller its radius, the greater its surface gravity.

Question 17

Most bodies in the solar system are in elliptical orbits. What are artificial satellites used for?

Answer 17

For the communications and to observe the earth and space. The type of orbit of an artificial satellite depends on what it is used for.

Question 18

What are highly elliptical orbits are used for?

Answer 18

For communication in parts of the earth near the poles

Question 19

Where do satellites in circular geostationary orbits remain over?

Answer 19

Over one point on the earth and are used for broadcasting. These satellites move at 3070 m/s

Question 20

What will a satellite in a polar orbit eventually do?

Answer 20

Pass over all parts of the earth

Question 21

What do low earth orbits need least of?

Answer 21

Needs the least fuel for launching satellites. These satellites move at around 7500 m/s

Question 22

A satellite, planet or moon in a circular orbit has a constant changing speed as it travels, however what is constantly changing?

Answer 22

It’s direction is constantly changing. As velocity is a vector quantity, an orbiting body has a constantly changing velocity

Question 23

A moving object will continue to move in a straight line unless what happens?

Answer 23

Unless there is a force acting on it to make it change speed or direction.

Question 24

For a satellite in orbit, the gravitational force between the earth and the satellite is at what to the direction to the movement?

Answer 24

The gravitational force between the earth and the satellite is at right angles to the direction of the movement, so the force changes direction but not its speed.

Question 25

The gravitational force on a satellite in a low orbit is greater than that on a satellite in a high orbit. Why?

Answer 25

The satellite in the low orbit has to be moving much faster to stay in its orbit. If it slows down it will fall towards the earth. It gains speed as it falls, until it is moving fast enough to stay in a new lower orbit. If it goes low enough to encounter the top of the atmosphere, contact with the air will slow it down and it will eventually fall to earth.

Question 26

The sun provides enough energy to keep earth at a temperature that supports life. However one day it will become a giant red star. When this happens, what happens?

Answer 26

When this happens it will expand and may even swallow up the earth. Long before that the extra heat of the earth experiences will kill all life

Question 27

What is a nebula?

Answer 27

A nebula is a cloud of dust and gasses (mainly hydrogen). These materials can be pulled together by their own gravity. As the cloud contracts it becomes denser. The hydrogen becomes hotter as it spirals inwards and may even start to glow. As more mass is attracted, the clouds gravitational pull gets stronger and heats the material even more. This is a proton star.

Question 28

What happens when the temperatures and pressures in the centre of a protostars become high enough?

Answer 28

Eventually the temperatures and the pressures in the centre of the protostar become high enough to force hydrogen nuclei to fuse together and form helium. Fusion reactions like this release as electromagnetic radiation. This outward pressure from the hot gasses just balances the compression due to gravity. The star is now in the main sequence part of its life-cycle. Our sun is in the stage of its life cycle.

Question 29

How long do stars of similar sizes to our sun remain stable for?

Answer 29

About 10 billion years. When they have fused most of their hydrogen into helium, the core is not hot enough to withstand gravity and it collapses. The outer layers expand to form a red giant star, much larger than the original star.

Question 30

What other fusion reactions happen inside red Giants?

Answer 30

Such as combining helium nuclei to form heavier elements. The star remains as a red giant for about a billion years before throwing off a shell of gas. The rest of the star is pulled together by gravity and collapses to form a white dwarf star. No fusion reactions happen inside a white dwarf and it gradually cools over about a billion years to become a black dwarf.

Question 31

What is the life cycle of a star like our sun?

Answer 31

Cloud of gas
Protostar
Main sequence star
Red giant
Shell of gas 
White dwarf

Question 32

Describe the life cycle of massive stars

Answer 32

Stars with more mass than the sun are hotter and brighter. They fuse hydrogen into helium faster, and then become red supergiants. At the end of the red supergiant period the star rapidly collapses and then explodes in a supernova. The outer layers of the supergiant are cast off and expand outwards. If what is left is four or more times the mass of the sun, gravity pulls the remains together to form a black hole. The gravitational pull of a black hole is so strong that not even light can escape it. If the remains are not massive enough to form a black hole, gravity pulls them together to form a very dense star called a neutron star

Question 33

What is the life cycle of a massive star?

Answer 33

Cloud of gas
Protostar
Massive main sequence star
Red supergiant
Supernova
Neutron start or black hole

Question 34

Why cannot we see black holes directly?

Answer 34

We cannot see black holes directly because light cannot escape from the, however they pull in gases from the space around the,, and these become very hot as they fall into the black hole. The hot gases emit radiation that we can detect

Question 35

As an emergency vehicles siren travels away from you, it’s pitch gets lower. What is this?

Answer 35

The Doppler effect

Question 36

What does the pitch of a sound depend on?

Answer 36

The pitch of a sound depends on the frequency of the sound wave. The sound waves behind a moving sound source become stretched, which makes their wavelength longer. This in turn lowers their frequency and so we hear the sound as a lower pitch. The opposite happens in front of the sound source. This only happens if the source of the sound is moving relative to the observer. If you are travelling in a car with the same velocity as the vehicle with the siren, it sound would not have appeared to change.

Question 37

The visible spectrum of light from stars contains patterns of dark lines. If these are red-shifted (moved towards the red end of the spectrum), what is the star doing?

Answer 37

Moving away from us. The further the lines are shifted, the faster the star is moving relative to us. The red-shift is a measure of how far along the spectrum the lines have moved.

Question 38

What happens if a star is moving towards us?

Answer 38

The wavelength and frequency of the light waves become shorter and so the pattern of lines moves towards the end of the spectrum. (It’s blue shifted)

Question 39

In the 1920s what did Edwin Hubble (1889-1953) investigate?

Answer 39

He investigated how far the pattern of lines was shifted for around fifty galaxies in comparison to the sun. He discovered that they were almost all red shifted and concluded that these galaxies were moving away from us. He found that the further away a galaxy is, the greater its red-shift and so faster it is moving away from us. We interpret this relationship to mean that the universe is expanding

Question 40

Go to page 125

Answer 40

And look at the diagram

Question 41

By measuring the red-shift of galaxies and other distant objects, we know that more distant objects are moving away from us faster than closer ones. This can be explained if the universe is expanding. What do astronomers use this information and other data for?

Answer 41

To work out theories that explain the origin and present state of the universe. One of these is known as the Big Bang theory, first suggested in the 1920s. This says that the whole universe and all matter in it started out as a tiny point of concentrated energy about 13.5 billion years ago. The universe expanded from this point and is still expanding. As the universe expanded, gravity caused matter to clump together to form stars

Question 42

What is an alternative theory to the Big Bang theory?

Answer 42

The steady state theory which was suggested in 1948. This theory says that the universe has always existed and is expanding. New matter is continuously created within the universe as it expands

Question 43

In 1964, two radio astronomers who were building a radio telescope detected microwave signals coming from all over the sky. At first they thought it was a fault in the equipment, but then they realised the signals were real. What did the astronomers realise?

Answer 43

The astronomers realised that this was the radiation predicted by the Big Bang theory. The Big Bang theory says that huge amounts of radiation were released at the beginning of the universe. Because the universe is expanding, the wavelength of this radiation has increased and so now is only detectable as microwave radiation. It is called cosmic microwave background (CMB) radiation

Question 44

Both the steady state theory and the Big Bang theory says that the universe is expanding. Can these theory’s be supported?

Answer 44

Observations of red-shift in the light from other hoaxes can be used as support for both theories. However CMB radiation provides supporting evidence for the big band theory only. The steady state theory cannot explain the CMB radiation. As there is more supporting evidence for it, the Big Bang theory is accepted by most astronomers today.