IOP Institute of Physics

# Experiments

Sunlight and space travel

1. Slide 2

Aims/Facts

• To establish that the Sun is very much further away from Earth than the Moon and both distances are very large compared to distances on Earth.
 Activity Discussion Ask them what the speed limit is on a motorway.Ask how far they would travel if they were driven at 70mph for 1 hour and give an example of a nearby city that they might have reached. Then continue with the idea of the time to drive to a distant city. Note - the places named on the slides should be changed for each school. The first few slides allows them to discuss their ideas of fast speeds and to try grasp some understanding of the distances between the Earth, Moon and Sun. Explain that these are thought experiments or mental space journeys.

2. Slide 3

Aims/Facts

• The Moon is a very, very long way away from the Earth compared with distances between cities.
 Activity Discussion Explain that if it were possible to drive off to the Moon it would take 140 days if a steady 70mph were maintained. They might point out that the petrol would run out or the driver would need food but explain that it is a thought experiment that overcomes problems.

3. Slide 4

Aims/Facts

• The Sun is very, very much further away from Earth than the Moon.
 Activity Discussion Ask them to imagine being driven all the way to the Sun and ask them to guess how long it would take. They might vote. At 70mph, time taken is about 150 years. (Two lifetimes) They enjoy discussing the problems with travelling for such a long time. This emphasises the huge distance.

4. Slide 5 and 6

Aims/Facts

• Light moves very, very quickly through space. It takes about 8 minutes for light to travel from the Sun to the Earth.
 Activity Discussion Explain that light travels very fast indeed. The ask them to guess how long it takes for light to travel from the Sun to the Earth. Take the opportunity to point out that the Sun is a powerful source of light and heat. Hazard: they must not look at the Sun.See safety notes

5. Slide 7

Aims/Facts

• Light travels in straight lines.
 Activity Discussion Point a bright torch across the room and shake chalk dust from a duster in the beam of light so that they can see that light travels in straight lines.See Apparatus List Discuss what happens when something gets in the way of the light. Hazards: Laser pointers should not be used and when shaking the board duster ensure that it is well away from the children.See safety notes

6. Slide 8

Aims/Facts

• Light cannot bend round a barrier. When light is blocked by objects, shadows are formed.
 Activity Discussion Shadows are formed when some light is blocked out.Show slide 9 without the lower wording up. Hold your hand in the projector beam to make shadow shapes on the screen. Volunteers may be able to make animal shapes etc. Show that varying the position of the hand varies the size of the shadow. This may be covered quickly if it has already been studied.

7. Game with sheet

Aims/Facts

• Shadows are similar in shape to the objects forming them.
 Activity Discussion See Apparatus ListAsk for two tall volunteers to hold up a large white sheet close to the front row of children. Then ask for two more volunteers to go behind the sheet. One to wave arms etc as the second points a bright torch so that shadows are formed on the sheet. Stand to one side during the demonstration with the sheet so that you can see the class and keep control during this fun activity. Discuss the changes in the shadow as positions change.

8. Slide 10 - Day and night

Aims/Facts

• During daytime the Sun light reaches half the globe. During one day the Earth rotates once on its axis.
• A day = 24 hours
 Activity Discussion Hold up an inflatable globe. Ask a volunteer to shine a bright torch at the globe across the front of the class so that the children can see that one side is illuminated and the other in shadow. Rotate the globe slowly.Show slides 11, 12 , 13.Ask how long it takes for the Earth to rotate once - 1 day.(Point out that pictures taken from space, like in Slide 12, prove that the Earth is a sphere – i.e. a ball.) Discuss the fact that the part of the Earth with the Sun shining on it is in ‘daylight’ while at the opposite side of the Earth it is night.Compare the diagram on slide 11 with the simulation on Slide 12 and discuss the fact that, during 24 hours, the Earth will move round slowly so that each part has daylight.

9. Ask for a volunteer who should stand at the front looking towards the class.

Aims/Facts

• The Earth takes 365 days to orbit (rotate around) the Sun. 365 days = 1 year.
• The Earth rotates 365 times during the time it takes to orbit the Sun once.The Earth’s axis is tipped by 23˚.
 Activity Discussion Point a bright torch onto the child as ask him/her to turn round slowly. Point out that you and the torch are acting as the Sun and the volunteer is the Earth. Ask whether the Earth just rotates or whether it also moves. Encourage the child to move around you – eventually rotating slowly to simulate the movement of the Earth round the Sun. Ask how long it takes for the Earth to move round the Sun once – 1 year. During the discussion ask how many times the earth rotates during a whole year. Then ask how many times the volunteer should have spun round whilst moving round you. (Hazard- do not allow the child to try to spin rapidly so becoming dizzy and possibly falling.)Point out that the child is standing upright to make a better demonstration the child should lean over at 23˚ to the vertical because the axis of the Earth is tipped. (The word axis might need explanation.)

10. Slide 14

Aims/Facts

• The Sun appears to move across the sky in a regular way every day.The Sun is highest in the sky at noon. The apparent movement of the Sun is caused by the spinning of the Earth on its axis.
 Activity Discussion During the day the position of the Sun in the sky varies. This is because the earth is turning on its axis. Slide 14 is animated to show the sun rise then sink in the sky. Discuss whether the Sun shines in at same place in the classroom during the day. Point out that the pattern of movement is similar each day.(The class may have done an exercise where they mark the position of the sun on a window during a day.)

11. Slide 15

Aims/Facts

• Shadows caused by the Sun can be used to tell the time.
 Activity Discussion Show the animated slide of the shadow of the stick moving during the day. Point out that this can be used to tell the time and the effect is used in a sundial. Please allow time for the Sun and stick to move in the animation. Discuss sundials – often seen on or by old buildings.(Check with the teacher whether the children have done a standard activity marking the shadow of a stick during a day. If so remind them about it.)

12. Slide 16

 Activity Discussion Tell them about the plans for the Solar Pyramid that will be built. To be built near the M1 in Derbyshire, England, UK. It will stand 58 metres (over 190ft) high, making it the worlds’ biggest functioning timepiece! Slide 17 shows one of the towers of the huge pyramid which acts a sundial.(The two secondary arms also have astronomical significance as one is aligned toward the point on the horizon where the Sun rises and the other to where it sets at the time of the Summer Solstice, the longest day of the year.)

13. Slide 18 - The seasons

Aims/Facts

• In winter the weather is colder than in summer.
 Activity Discussion Point out that the Sun shines all year providing light and heat but it is colder in winter than in summer. Ask what causes this effect? Please allow time for the Sun to move in the animation. Ask whether they notice any difference in the path of the sun across the sky during winter and summer. They may comment that shadows caused by the Sun generally are longer during winter.

14. Slide 19

Aims/Facts

• The Sun rises in the East and sets in the West.The Sun rises higher in the sky in summer than in winter.
 Activity Discussion This is animated to show the Sun rises higher in summer than in winter. The slide also shows that days are longer in summer than winter. In discussion point out that the Sun rises at a point further east and sets at appoint further west in summer than in winter (some websites incorrectly show the sunrise at the same point on the horizon for summer and winter). Discuss the differences the children notice between summer and winter.

15. Slide 20

 Activity Discussion Then slide 20 shows that this is because light reaching the Earth during winter is at smaller angle to the surface ( a greater angle to a normal to the surface). It is not obvious to young children why this should result in colder conditions. Ask what makes it colder in winter than in summer. They may answer that the Earth is further from the Sun in winter. It is true that the orbit of the Sun is slightly elliptical but the Earth can be closest to the Sun in January.

16. Demonstration

Aims/Facts

• Extra to KS2: The seasons are caused because the Earth is tipped on its axis so that during our summer the earth is tipped towards the sun and during our winter, the Earth is tipped away from the Sun.
 Activity Discussion See Apparatus ListShine a bright torch onto a dark umbrella so that a bright circle of light can be seen. Explain that the torch represents a beam of light from the Sun and the umbrella, the surface of the Earth. Point out that during winter the Sun is lower in the sky so lower the position of the torch. Change the angle that the light reaches the umbrella so a dimmer oval of showing that the concentration of heat and light reaching the surface is reduced so it is cooler.See safety notes on spring umbrella. Repeat the demonstration and discuss the effect.Also the Sun is above the horizon for a shorter time than in Summer so the total heat reaching the region is less than in Summer. The light travels slightly further through the atmosphere in winter so more heat is absorbed.Explain that the seasons are caused because the axis of the Earth is tipped by 23 degrees.Point out that during our summer it is winter in the Southern Hemisphere.

17. Game

 Activity Discussion Each group should have a torch and a piece of card or a large brown envelope. They should shine the torch on the card at different angles so they see the area covered varies with angle- keeping the distance of the torch from the card the same throughout.See Apparatus List Emphasise that the effect is for heat as well as light and discuss the effects if first one stands in front of a radiant heater and then stands to one side. (You are advised NOT to take a heater into the school.

18. Slides 21, 22 - Moon

Aims/Facts

• The Moon is not a source of light. The Moon reflects light from the Sun to the Earth.The Moon takes approximately 28 days to orbit the Earth.The changing appearance of the Moon over 28 days provides evidence for a 28-day cycle. The Moon revolves once on its axis for each orbit of the Earth so that the same side of the Moon always faces the Earth.
 Activity Discussion The Moon is a satellite of the Earth. That means it orbits the Earth continuously, taking about 28 days per orbit.The Moon does NOT give out light but reflects sunlight to the earth.Demonstration 1 with the ball.Stand at the front of the class and ask them to imagine that the Sun is shining from the back of the class so that one side of the ball is illuminated brightly. Turn the ball so that the white side is towards the class. Then move towards your left and stand at the side of the class still holding the ball so that its white side is facing the back of the class (full Moon). The ball will appear half white and half black to the children (last quarter). Then as they watch you move towards the back of the class keeping the white side towards the back of the class, they will see less and less of the white part of the ball until, when you reach the back of the class they see only the black side (new moon). Explain that the Moon takes 28 days to move once completely round the Earth. So your movement so far represents 14 days.Continue to move round so that they see some white and eventually when you are at the front they see the full moon. In demonstration 1 the ball does not rotate, which is incorrect. A more accurate demonstration (2) uses a white ball with a face painted on it. As you move round the class, the face on the ball must always face the children. The black and clear cover is slid round so that the clear part always faces the back of the class and the black part represents the part of the Moon in shadow. (see the apparatus list for details) It is not necessary to do both demonstrations but repeating the one you choose will be helpful.

19. Slide 23

Aims/Facts

• Reinforce ideas.
 Activity Discussion Talk through the animated slide so that they understand the phases of the Moon clearly. (Each mouse click moves to anther discussion point.)Take the opportunity to answer questions on Slide 24. These are examples of bad astronomy seen in films. Suggest they watch out for examples in films that they see. Slide 24 - They should answer - the Moon changes appearance after a few days. (It only takes 7 days to change from a new Moon to a Half Moon.)- the full Moon is so bright that it is difficult to see stars.- in a bright room our pupils are contracted so stars are too dim to see.- refer back to dusk on Slide 12.

20. Slide 25 - Game

Aims/Facts

• The sun and the Moon look the same size because they are different distances from the Earth.
 Activity Discussion Hand out a cardboard tube, a small object and a large object to each group. One child looks through the tube and another holds the small object so it appears to fill the whole of the end of the tube. The small object should be moved slightly out of line. Then a third child should hold up the large object and move it so it just appears to fill the end of the tube. The distances should be compared.They will find that large objects need to be much further from the tube than small ones. It is best to demonstrate this first at the front and discuss the distances before allowing the groups to try the game.Explain that this helps to understand why the Moon and the Sun appear the same size. Refer back to the distances discussed at the start of the session.Explain that the Sun is very much further away than the Moon.

21. Slide 26

Aims/Facts

• Extra to KS2: An eclipse of the Sun occurs when the Moon blocks the sunlight from reaching the Earth.
 Activity Discussion On rare occasions it goes dark in the daytime.Game - Slide 27They should hold up a circle of cardboard and look at it with one eye, at a distance so that it just covers the picture of the Sun. Explain that the card represents the Moon and although it is smaller than the picture of the Sun, it blots out the light from reaching their eye. Just as the Moon can blot out light from the Sun reaching us. Explain that this is called an eclipse. Slide 29. Sometimes the Moon is not quite in line and a partial eclipse occurs. During discussion Slide 28 will help.Explain that sometimes the Sun Moon and Earth are not quite in line. Then there is a partial eclipse. These are much more common. If possible tell them when the next partial eclipse can be seen in the UK.The last total eclipse visible from the UK was seen in southern England on 11 August 1999. An animation of an eclipse on 29 March 2006 that was visible as a partial eclipse from the UK can be seen at http://www.eclipse.org.uk.The next eclipse of the Sun visible from the UK will be on 1 August 2008 and will be seen as a partial eclipse from the UK.

22. Slide 30 Eclipse of Moon

Aims/Facts

• Extra to KS2: An eclipse of the Moon is caused when the Earth blocks the sunlight from reaching the Moon.
 Activity Discussion When the Moon moves into the shadow of he Earth it receives no light from the Sun so it cannot be seen. This is an eclipse of the Moon. Show the animated slide. Explain that this is different from the situation for a new moon because then the moon is between the earth and the Sun.

23. Take the opportunity to revise using Slide 31.

24. Slide 32

 Activity Discussion Explain that knowledge about distances and positions of the Earth, Moon, Sun and Planets have made space travel possible. The picture shows the space shuttle leaving the international space station. Slide 33 shows this enlarged. Encourage a discussion about the benefits- and whether they would like to be astronauts- point out that many astronauts have studied physics (most have studied science).

25. Slide 34

 Activity Discussion Venetia Burney, when 11 years old, suggested the name Pluto when it was discovered in 1930. The probe that left to take a closer look at Pluto early in 2006 will not get there until 2015 when they will be ... years old.Slide 35See websites for more information. Link back to the time worked out to reach the Sun and Moon at 70 mph and explain that space probes travel much faster than that.The probe will visit the Moon after 9 hours – it took Apollo capsules 3 days. As it leaves Jupiter behind it will be travelling at 21 km per second (13 miles per second). Use the discussion to revise and reinforce their understanding of the large distances and speeds involved.

26. Slide 36

Aims/Facts

• There is a lot more for scientists to find out.
 Activity Discussion Finish by pointing out that they should keep asking questions – there is lots for them to find out. BUT there is lots that no-body knows yet and that scientists of the future will be working on and they might be the ones who discover the answers to the puzzles. Keep asking questions.