Introduction

 

About our work

The Moon is Earth's closest neighbour in space and except from the sun it is the brightest object on the sky, yet we felt that we didn't know very much about it. Therefore we decided to learn more and we also wanted to do an exercise that young people all over the world can use to get to know the Moon better. We have learned a lot and we hope that this text will teach you something !

E-mail:

Ella Carlander
Agnes Johansson
Lisa Spaak
Roger Andersson (our teacher)

Västerhöjdsgymnasiet
Skövde, Sweden.
2002-10-31

     

Earth's moon

 

History

Our closest neighbour in space is the Moon. Man has since the beginning of time been very fascinated by this great big shining thing that gives us light during dark nights. For thousands of years the Moon has been worshipped as a god and it has also often been considered to be "the sun's bleak cousin". The old Greeks called it Selene, sister of the king of the sun, Helios. Selene helped Helios with his work, to give light to the Earth, during the night. There are also stories about how Zeus (Jupiter) fell in love with Selene and that's probably one of the reasons why people think that love is connected with the Moon. Even nowadays people find it very romantic when there is a full Moon. But not only nice things like love are connected to the Moon. Long ago people thought that the Moon could make you mad. The English word for a mad person is 'lunatic'. 'Luna' is the Latin name for the Moon (Newth, 1992). Even now, when we know much more about it many people think that the Moon can make us do evil things. Some people also say that they have problems sleeping when the Moon is full, not only because of the strong light.

Man thought for ages that the Earth was the centre of the universe, i.e. we had a geocentric way of looking at the world. We thought that everything was orbiting around the Earth, not only the Moon but also the sun and the stars. Now we know that the sun is the centre of our solar system and only the Moon is orbiting around us!

 

Trips to the Moon

People have always been thinking and wondering about space and their qualities like, for example: the planets, the stars, the Moons and lots of more things. When the scholars for the first time were planning to build spacecrafts to get answers to all their questions it was as late as during the 1940's. It wasn't that easy just to build a spacecraft; they needed a lot of money too. When they had talked about money, there were only the USA and the former Soviet left.

It became a competition between the two countries. They both wanted to come out in the space first. Soviet won. In April 1961 Jurij Gagarin travelled around the earth for 108 minutes in Vostok 1. But Soviet didn't win the whole competition; they were not first to land on the Moon. The USA got there first. In 1962 they started a project called the project of Apollo. (Video: Teknik och vetenskap: Rymdtekniken och månen)

 

The project of Apollo

The rocket (see pictures below), which finally brought the first people to the Moon, was a Saturn's type with three steps driven by liquid. When they started the rocket had a weigh of about 2900 ton. In the launching moment the consumption of the fuel were 20 000 litre/second. The three rocket steps were disconnected as the contents in their tanks had been used. (http://www.geocities.com/ResearchTriangle/1510/projekten.html)


  The carrying rocket The Moon vessel  

Apollo - 9
It did the first test with docking between the command module and the Moon lander, an important operation for the astronauts so they could go back to Earth. - Mars in 1969 McDivitt, Scott, Shcwelckraft. (Video)

Apollo - 10
It was the first general repetition in human presence. The meaning was now that every part should work before the finally landing and visit on the Moon. It did work! - May in 1969 Stafford, Young, Cernan. (Video)

Apollo - 11
It took the first human beings too the Moon. People had been worried about the surface on the Moon and if it should hold for the landing but it did. Apollo 11 landed on the Sea of Tranquillity. It was an enormous exploit; everybody followed the astronauts by TV and radio over the whole world. When Neil Armstrong took his first step on the moon he said, "That's one small step for a man, one giant leap for mankind" (Nationalencyklopedin, 1989, band 1).

They placed the American flag on the Moon and gathered some material to bring back home. They succeeded. In all, they were on the surface of the Moon for about two and a half-hour. - July 20th in 1969 Armstrong, Aldrin, Collins. (Nationalencyklopedin, 1989, band 1 and Focus, 1964)

Five other landings followed. Apollo 17 became the end of this beginning of human movement into the universe.

Apollo - 17
The last Apollo mission to the Moon, Apollo 17, left Earth on December 7 in 1972 (Video). It landed near the southeastern edge of Mare Serenitatis in the Valley of Taurus-Littrow.

 

Where does the Moon come from?

Despite all investigations the question about the origin of the Moon has not been determined. One of the oldest and most popular opinion is that the Moon once was a part of Earth and that it in some way broke loose and was thrown away. The chemical analysis of the material from the Moon does not contradict to this theory, but it is difficult to find a reason to why the Moon and Earth separated and why the Moon was bound to Earth. One possible explanation is that long ago a celestial body might have collided with Earth. The crash made much of the outer layer of Earth followed the crushed parts out into space. All this material spread around Earth and after some time it came together and formed a new celestial body - Earth's moon! Computer models that try to imitate reality show that this is a possible explanation (Bra Böckers Lexikon, 1998).

Another theory suggests that the Moon was created somewhere else in the universe and then captured by the gravity of Earth. The probability that an object with the size of the Moon moving towards Earth actually would end up in an orbit instead of colliding or just simply pass is very small.

The third theory implies that Earth and the Moon were created next to each other when the solar system was created. What the theory cannot explain is how or why two such big objects could be created so close to each other, within a distance of "only" 384000 kilometres (Fraizer, 1988).

 

The phases of the Moon

It looks like the Moon itself is glowing, but that's not true. It's only reflecting light from the sun. It also seems as if the Moon has different shapes on different days. But the Moon is always spherical; it's the way we see it that makes the difference in shape. We say that the Moon is in different phases (Rådbo, 1998).
The Moon is moving around Earth because of Earth's gravitational pull. The sun is always shining on one half of the Moon, just like it does on Earth. We have one side with day and one side with night and it's the same with the Moon. The Moon phases are due to that we see the sunlit part of the Moon from different angles as the Moon moves around Earth (BBL).

 

 

When there is a new Moon, the whole sunlit side is turned away from Earth and we can't see it (A). The Moon is now close to the sun. One day later the Moon has moved so much so that we can see it as a crescent (B) right after sunset in the west. Six days later the crescent has increased in size so much that it has become a semicircle (C). It keeps on increasing its size (D) and one week later the Moon is full (E). After this the Moon starts to decrease in size (F-H) and one week later the Moon is half again. Yet another week and the Moon is new again. (BBL, Rådbo, Newth)

When we see the Moon as a crescent and it is illuminated from the right the Moon is close to the sun in the sky. We then see the Moon during the day. The full Moon rises in the evening, culminates (it is as high as possible to the south) in the middle of the night and sets in the morning. The height over the horizon when the Moon is in its southerly position varies with the seasons. (Newth)

 

What we see

The Moon is always showing us the same side because it rotates around its own axis exactly as fast as it rotates around Earth, almost anyway. When the Moon has travelled one quarter of a revolution around Earth it has also rotated one quarter around its axis. The fact is that the Moon seams to jerk a little so that sometimes it is possible to see a little of the backside. This is because its orbit is not circular but elliptic.

Earlier, before space probes and astronauts flew around the Moon and took pictures of it, no one had seen the back of the Moon. This changed when Soviet Luna 3, launched in 1959, took photographs of it in 1959 (BBL, http://asp.vader.se/manen.asp). The two sides of the Moon are quite similar, but there are no "seas" on the backside. The "seas" looks darker and the lighter coloured areas are called land. The "seas" are not actually seas, but when the Italian scientist Galileo observed it four hundred years ago he thought some areas looked like big seas. Therefore he called them marias, the plural form of the Latin word mare, which means sea. The "seas" turned out to be basaltic flows, hardened lava. The lava flowed long ago out of the fissures of the Moon. Altogether the seas cover half of the visible lunar surface and are actually plains and often surrounded by mountains or ridges.
(http://www-spof.gsfc.nasa.gov/stargaze/SMoon2.htm)

 

Craters

The surface is also covered with craters and mountains that vary in size. The highest summits on the Moon are over 10 000 meters! (Det Bästas Stora Världsatlas, 1978) The craters have mostly been created of big "space rocks" that have crashed onto the Moon surface at enormous speed. The high speed is possible because the Moon has no atmosphere that slows down the objects. (Rådbo) Probably the craters and mountains are very little due to volcanic activity. Craters that resembles to the ones on the Moon has been found on Mars, Mercury and Venus and the scientists suppose that they represent the natural appearance of an uninhabited planet with solid surface. (BBL, DBSV) The majority of craters probably date back to the early days of the solar system.

Most of the craters on the side of the Moon facing Earth have been named after famous persons in the history of science like Tycho, Copernicus and Ptolemaeus. Formations on the other side of the have more modern references such as Apollo, Gagarin and Korolev. (http://hem.passagen.se/siw/rymden/jordsat.htm)

 

 
 

Measurements

The Moon has a diameter of 3 476 kilometres by the equator. That is one fourth of the diameter of Earth. The surface of the Moon is about 38 million square kilometres, which is four times the area of Europe. Its circumference is about 10940 kilometres. It takes 27,3 days and nights to complete one turn around Earth. It uses the same time to rotate around its on axis and as a consequence of this it always turns the same side towards Earth. (http://asp.vader.se/manen.asp)

 
 

 

Distance

The mean distance between the Moon and Earth is 384 392 kilometres, but varies from being 356 410 kilometres at its minimum to 406 680 kilometres at its maximum. This means a difference of 10 % and consequently the apparent size of the Moon also varies this much. Accurate measurements of the distance to the Moon are made with laser beams directed towards reflectors left on the Moon by Apollo astronauts. The distance to the Moon increases with 3,5 cm every year. (N. & M., 1987)

 

Is there water on the Moon?

In the centuries after Galileo's discoveries astronomers extensively studied the Moon. It soon became clear that the Moon does not have an atmosphere. They found out that the gravity on the surface of the Moon only is 1/6 as strong as the gravity on Earth. Therefore the Moon cannot keep gas molecules in an atmosphere like Earth. Water easily evaporates and is also soon lost and that is why there cannot be water freely on the Moon.

Astronauts bringing back rock samples from the Moon have reinforced the picture of a dry Moon. Opposite rocks from Earth that might contain water bound chemically there was no trace of water in the rocks from the Moon. Yet small amounts of water might exist, brought to the Moon by comets (http://www-spof.gsfc.nasa.gov/stargaze/SMoon2.htm). Frozen water reserves have been found in craters both on the north pole and on the south pole. The satellite Lunar Prospector that was launched in 1998 confirmed this. The reason to why there can be frozen water is that the places are permanently in shadow. (http://asp.vader.se/manen.asp)

Since the Moon does not have an atmosphere it is possible to see details on the surface with perfect sharpness. With instruments based on Earth astronomers can see objects down to the size of 300 meters. In purpose of more accurate studies they use instruments like space probes, earth satellites and lunar modules because the atmosphere of Earth is disturbing too much. (BBL)

The fact that the Moon does not have an atmosphere has some effects that might seam strange to us living on Earth:

  • The line between sun and shadow is sharp since there are no mist or haze that can soften the sudden change.
  • It is completely quiet because sounds are vibrations in air, and there is no air on the Moon.
  • There are no dusk or dawn; the day and the night, which are approximately 14 earth-days and nights, comes suddenly.
  • The changes in temperature are violent since there is no protecting layer of gas around the Moon that can damp the sunlight or keep the heat during the night. In the day the temperature can rise to 130°C and in the night it falls to -170°C.
  • There is no wind on the Moon, because it has no atmosphere. Therefore the footsteps of Neil Armstrong and his partner will remain on the Moon for millions of years. (DBSV)


What we do not see

The interior of the Moon has been investigated by experiments and by seismographs left by the Apollo astronauts. The experiments have shown that the inner of the Moon is warm: up to 1500K, which is approximately 1200°C. The seismographs have been studying natural moonquakes, meteorites and artificial impacts. Letting used rocket stages and lunar modules crash against the surface has created the impacts. (Nicolson & Moore, 1987) Seismographs on Earth register hundreds of thousands of earthquakes every year but the instruments on the Moon have only detected approximately 3000 per year. Most of them do not have more energy than a firework. Many of the quakes occur regularly and the scientists believe that they are caused by gravity between Earth and the Moon. (Fraizer, 1988)

 
 

Intersection of the Moon

The Moon can have a small core (1) rich in iron surrounded by a region that is partly melted (2). The solid mantle (3) is approximately 1000 km thick. The thickness of the crust (4) varies between 60 and 75 km. Moonquakes appear in the lower parts of the mantle. The lava that fills the "seas" on the surface comes from a depth of several hundred of kilometres.

 
 

Altogether 382 kg of stone samples were brought back to Earth by the Apollo and Luna programs. The scientists are, even 20 years after the latest Moon landing, investigating these samples. Most of the stones investigated seams to be between 3 and 4,6 million years old. (http://hem.passagen.se/siw/rymden/jordsat.htm) This implies that the Moon is approximately 4,6 millions years old.

 

Tidal water

Tidal water is caused by the gravity between the Moon and Earth. The force is stronger on the side of Earth turned towards the Moon and weaker on the side turning away from the Moon. The gravity makes the water in the oceans bulge on two sides of the planet. While Earth rotates around its own axis the swellings sweep along the planet. The tide returns about two times every day. That is because Earth rotates much faster around its own axis than the time it takes for the Moon to complete its revolution around Earth. The tide is delayed about 52 minutes everyday. When the sun and the Moon is in a line the force on the water gets extra strong and the tide reaches its maximum. (Mitton & Mitton, 1981)

 

Our exercise

This is an exercise for a group of children, perhaps a class, 8-10 years old. The children could be divided into groups of 2-3 persons. The task will last during approximately a month. The teacher will hand out instructions to the children and follow it up weekly in school. It is probably good to decide to which days the children would have this as homework, for example Mondays and Thursdays.

The children are going to study the phases of the Moon during a month, from one new moon to the next new moon. Twice a week the children will go out during the evening and have a look at the Moon. Then they are going to draw a painting or in some way note and show the appearance of the Moon. Sometime during the month or when the month is over the children should think about what might cause the different phases of the Moon. How is it changing and why is that? They could try to find information in our text or in another book about the Moon.

In the class the teacher could do follow-ups and let the children compare their results with each other every week. As a final task they will, in their groups, illustrate what they have learned using, for example, an electric torch, a football and an orange.

We hope that this exercise will learn the children more about our closest neighbour in space and that they might want to continue working with the Moon or perhaps other phenomenon more distant to us.

 
 
The figure shows one way for the children to describe what they have seen.
 
     

Earth's Moon compared with Io

 

 

We know that there in our solar system are 63 moons; Earth's moon is one of them. There are surely more then 63 in the whole Universe. Earth has, as we all know only one moon but most of the other planets have more than one. We know of sixteen moons around Jupiter, but it could have more. When the Italian scientist Galileo 1610 looked through his binocular he saw four moons around Jupiter. He named them Io, Europa, Ganymede and Callisto. These where the first discovered moons around another planet and it was a big event. They are still called the Galilean moons. Io is the one of them that is nearest to Jupiter.

 
     
  The mean distance between Io and Jupiter is 422 000 kilometres compared to the mean distance between our moon and Earth, it's 384 392 kilometres. Io has a diameter of 3 640 kilometres, a little more than our Moon with it's 3 476 kilometres. Though some of the things about our moon and Io seem to be almost the same there are also some big differences. Like for example: It takes our moon 29,5 days to complete one turn around Earth. Io spins a lot faster; it takes only 1,77 days! Another difference is that Io's surface is covered with sulphur. (BBL, Rådbo, 1998)

The moon is torn in different directions by the forces from Jupiter and the three other big satellites. The friction in the crust heat up the inner of Io and keeps it in liquid form. It spurts out through cracks in the crust with high speed like volcanoes. The Moon has very little or no volcanic activity; on Io there are plenty of volcanoes. It was the first time active volcanoes had been observed on another object in the solar system. Of course there are other differences too, but we have mentioned some of the bigger ones! (www.astro.uu.se/astnews/1999/November/99Nov5.html)

 
     
 

Sources

Most of the literature that we've used is Swedish and have Swedish titles.

 

Literature

Frazier, K., (1988). Planeten Jorden: Solsystemet (M. Saxner, Trans.). Amsterdam: Time-Life Books B.V. (Original work published 1985)

Mitton, J., & Mitton, S. (1981). Upptäck Astronomi ( C. Bernes, Trans.). Eskilstuna: Bonniers Bokförlag AB. (Original work published 1978)

Newth, E. (1995). Vår stjärnhimmel - en handbok för amatörastronomer (N. Heimbrand, Trans.). Bonnier Carlsen. (Original work published 1992)

Nicolson, I., & Moore, P. (1987) Vetenskapens Värld: Solsystemet (M. Fridlund, Trans.). Malmö: Fogtdals Förlag. (Original work published 1985)

Rådbo, M. (1998). Runt i rymden - Till alla frågvisa. Stockholm: Opal AB.

 

Encyclopedias

Bra Böckers Lexikon. (1979). Höganäs: Bokförlaget Bra Böcker AB

Bra Böckers Lexikon. Band 16 (Månen). (1987). Höganäs: Bokförlaget Bra Böcker AB

Det Bästas Stora Världsatlas. (1978). Stockholm: Reader's Digest AB

Nationalencyklopedin. Band 1 (Apolloprojektet) & 13 (Månsonder). (1989). Höganäs: Bokförlaget Bra Böcker AB

FOCUS Tekniken och materien. (1964) Stockholm: Almqvist och Wiksell/Gebers förlag AB.

 

Internet
http://www-spof.gsfc.nasa.gov/stargaze/SMoon2.htm (2002-10-04)
http://www.inconstantMoon.com (October 2002)
http://asp.vader.se/manen.asp (2002-10-04)
http://hem.passagen.se/siw/rymden/jordsat.htm (2002-10-04)
http://www.geocities.com/ResearchTriangle/1510/projekten.html (October 2002) http://www.astro.uu.se/astnews/1999/November/99Nov5.html (2002-10-30)

 

Video
Teknik och vetenskap: Rymdtekniken och månen. (Sent in SVT 1998). Sweden: UR.

 

Pictures
The Moon: http://www-spof.gsfc.nasa.gov/stargaze/SMoon.htm
Io: http://photojournal.jpl.nasa.gov/catalog/PIA02308