Physics

ASTROPHYSICS                Earth and Space

Key unit Competence

By the end of the unit, the learner should be able to illustrate and describe the general structure of the solar system.

My goals

By the end of this unit, I will be able to:

* illustrate and describe the general structure of the solar system.

* identify and explain scales for estimate astronomical distances.

* explain the phenomenon of eclipse and explain phases of the moon.

* differentiate inner, outer planets, comets, meteorites and asteroids.

* discuss Kepler’s laws and explain stars patterns.

* identify celestial coordinates.

Astronomical scales

Astronomy is the study of the universe, and when studying the universe, we often deal with unbelievable sizes and unfathomable distances. To help us get a better understanding of these sizes and distances, we can put them to scale.

Scale is the ratio between the actual object and a model of that object. Some common examples of scaled objects are maps, toy model kits, and statues.

Maps and toy model kits are usually much smaller than the object it represents, whereas statues are normally larger than its analog.

Our solar system is immense in size. We think of the planets as revolving around the sun but rarely consider how far each planet is from the sun or from each other. Furthermore, we fail to appreciate the even greater distances to the other stars. Astronomers refer to the distance from the sun to the Earth as one “astronomical unit” or AU = approximately 150 million kilometres. This unit provides an easy way to calculate the distances of the other planets from the sun and build a scale model with the correct relative distances.

Activity 1: Role play

Solar System Bead Distance Activity

We will construct a distance model of the solar system to scale, using coloured beads as planets. The chart below shows the planets and asteroid belt in order along with their distance from the sun in astronomical units.

First, complete the chart by multiplying each AU distance by our scale factor of 10 centimetres per astronomical unit. Next, use the new distance to construct a scale model of our solar system. Start your model by cutting a 4.5 meter piece of string (5.0 metres if you are doing the Pluto extension).

Use the distances in centimetres that you have calculated in the chart below to measure the distance from the sun on the string to the appropriate planet and tie the coloured bead in place. When you are finished, wrap your string solar system around the cardboard holder. Note that the bead colours are rough approximations of the colors of the planets and the sun,

Keep two important solar system facts in mind. The first is that the planets never ever align in a straight line. Occasionally skywatchers are treated to the sight of two bright planets apparently close together as viewed from our planet.

The second fact is that your string solar system is a radius of the orbits of the planets. To see how large the solar system is, hold the sun in one location and swing the planets in a circle around it. If you move counter-clockwise you will be moving the planets in the direction they move as viewed from above their plane. The whole circumference of the solar system probably will not fit into your classroom.

Materials:

* Planet beads (large craft pony beads in 11 colours) roughly. approximating the appearance of the planets and the sun.

* Five metres of string for each learner.

* Small piece of cardboard to wrap solar system string around (10 cm x 10 cm).

* Metre sticks or rulers with centimetre markings for each learner or group to share.

* Learner calculations table, one for each learner.

Background

To speed up the activity, the string may be pre-cut and a set of solar system beads may be put into a plastic zip-lock bag for each learner. Also, a measured marking grid can be put on a table top so you can mark their measured distances and then tie off the beads. If the pre-marking method is used, extra distance must be added to each planet distance to accommodate the string within each knot (approximately 4 centimetres for a double knot around the bead). Tape newspaper to the surface where you will be marking your strings so you do not mark up the counter or floor.

Procedure

1. Convert the various astronomical unit distances to centimetres and complete the chart on the student calculations table.

2. Measure and cut a piece of string 4.5 metres long.

3. Using the calculated centimetre distance, tie the bead onto the string using a double knot.

4. When finished with the activity, wrap the solar system string (with beads) around the cardboard holder.

Learner Calculations Table:

Viewed from Earth it is difficult to gauge the scale of the universe but astrophysicists have developed techniques to help to do this. Stars and galaxies are so far away than a new unit of distance measurement, the light-year (ly),is often used. For light travelling at 3 x 108m/s, the distance traveled in one year is:

For specifying distances to the Sun and Moon, we usually use metres or kilometres, but we could specify them in terms of light. The Earth-Moon distance is 384 000 km, which is 1.28 light-seconds. The Earth-Sun distance is 1.5 x 1011 m, or 150,000,000 km; this is equal to 8.3 light-minutes. Far out in

our solar system, the ninth planet, Pluto, is about 6 x 109 km from the Sun, or 6 x 10-4 ly. The nearest star tous, other than the sun, is Proxima Centauri, about 4.3 ly away. (Note that the nearest star is about 10,000 times farther from us than the outer reaches of our solar system.)

The Milky Way or our Galaxy is about 100 000 ly across; our sun is located on one of the spiral arms of the galaxy at a distance of 28,000 ly from the galactic centre.

Career centre

Learn more about career in physics and engineering about the general structure of solar system.

Sun-Moon-Earth System (Eclipses and Phases of the Moon)

Eclipses (lunar and solar eclipses)

Activity 2

Eclipses in classroom

Building the Sun-Earth-Moon system described below will allow your class to discover how and why eclipses happen. They will be able to understand exactly what they are seeing if ever they see a real eclipse.

Materials

For each model, you will need:

* Adhesive tape

* Glue

* Two cardboard tubes (e.g. empty toilet rolls)

* Torch

* Scissors (suitable for cutting cardboard)

* Aluminum foil

* Sturdy but bendable wire (35-50 cm long)

* Styrofoam ball the size of a large orange

* Ping pong ball (or a Styrofoam ball of a similar size)

* Large strip of cardboard (about 60cm in length and not less than 20cm in width)

* Stack of books or magazines

Procedures

1. Divide the class into groups of three or four. Give each group their own materials to make the model.

2. Take one cardboard tube and make a series of small (2 cm) even, vertical cuts around the circumference of each end.

3. At each end, bend the cut pieces out, and then stand the tube upright. At the top, the cut edges should fan out like a flower.

4. Using adhesive tape, fasten one end of the cardboard tube to the strip of cardboard; this is the base of the model. The tube should be at least 30cm from one end of the cardboard strip.5. Using tape or glue, attach the larger ball to the open flower of the tube. This ball is Earth.6. Cover the smaller ball with aluminum foil, shiny side out. This is the Moon.

7. Insert one end of the wire into the top of Earth, so that the wire is vertical.

8. Measure a finger’s length along the wire. Bend the wire at a right angle to give a horizontal arm.

9. Insert the other end of the wire into the Moon.

10. About halfway between Earth and the far end of the cardboard strip, measure a finger’s length along the wire and bend it downwards at a right angle, toward the cardboard base. The Moon’s equator should be at the same height as Earth’s equator.

11. Balance the torch on a stack of books or magazines at the other end of the cardboard strip from Earth. Make sure the height is correct: the middle of the torch beam should hit Earth’s equator. If the beam is too diffuse, attach the second cardboard tube to the end of the torch to direct the light horizontally. Ensure the beam hits the nearest half of Earth and the Moon directly. If the beam is not bright enough, move the stack of books closer.

Eclipse, in astronomy is the obscuring of one celestial body by another, particularly that of the sun or a planetary satellite. Two kinds of eclipses involve the earth: those of the moon, or lunar eclipses; and those of the sun, or solar eclipses. A lunar eclipse occurs when the earth is between the sun and the moon and its shadow darkens the moon. A solar eclipse occurs when the moon is between the sun and the earth and its shadow moves across the face of the earth.

Activity 3

Create lunar and solar eclipses

Materials

The required materials are ones in activity 2

Procedures

1. Set the apparatus in activity 2

2. Create a solar eclipse. Stand facing the torch and swing the wire around until the Moon casts a shadow on Earth; if necessary, dim the lights. The Moon is now between Earth and the Sun and is blocking the sunshine for some people on Earth. Point out that only people directly in the shadow see a complete eclipse of the Sun. You can show how the shadow moves by slowly rotating the wire.

3. Now create a lunar eclipse. Stand facing the torch and swing the wire so that the Moon is behind Earth. No light should be hitting the Moon: Earth is between the Sun and the Moon, casting a shadow over the entire Moon. Explain that unlike during the solar eclipse, the entire ‘night side’ of Earth can see the lunar eclipse.

Lunar Eclipses

The earth, lit by the sun, casts a long, conical shadow in space. At any point within that cone the light of the sun is wholly obscured.

A total lunar eclipse occurs when the moon passes completely into the umbra. If it moves directly through the centre, it is obscured for about 2 hours. If it does not pass through the centre, the period of totality is less and may last for only an instant if the moon travels through the very edge of the umbra.

A partial lunar eclipse occurs when only a part of the moon enters the umbra and is obscured. The extent of a partial eclipse can range from near totality, when most of the moon is obscured, to a slight or minor eclipse, when only a small portion of the earth’s shadow is seen on the passing moon. Historically, the view of the earth’s circular shadow advancing across the face of the moon was the first indication of the shape of the earth.

Solar eclipses

In areas outside the band swept by the moon’s umbra but within the penumbra, the sun is only partly obscured, and a partial eclipse occurs.

Phases of the moon

Key Facts about Space and Space Exploration/The Moon:

• There are different phases of the Moon that make it appear a little different every day, but it looks the same again about every four weeks.

• The Moon can sometimes be seen at night and sometimes during the day.

Activity 4

Moon Discussion

Materials:

* “Moon Phases Cards”

* Scissors

* Pencil or crayons (for “Moon Phases Chart”)

* “Moon Phases Chart”

To Prepare before

* Print out one “Moon Phases Chart” per learner. Print out one copy of the “Moon Phases Cards” handout for every 3-5 learners.

Discussion (Key questions)

a) Describe when the best time is to see the moon. Can the moon also be seen during the day?

b) Does the moon look the same every time when you look at it? Explain how it changes.

c) According to you how many days it takes for the moon to travel around the earth and what do we observe as different phases?

d) Hold up the “Moon Phases Cards” and point out the different phases that the moon goes through (Figure 12.3)

Fun facts to share:

• We can only see half of the moon from earth, since the other side is always turned away from us.

• As the moon travels around the earth, we see different fractions of the moon, as it is lit by the sun.

• “Waxing” means growing and is used to describe the moon as it grows from new moon to full moon.

• “Waning” means shrinking and is used to describe the moon as it gets smaller from full moon to new moon.

• The “first quarter” is when the moon has completed ¼ of its orbit around the earth. This is when the moon looks like a “half moon.”

• The “last quarter” is when the moon has completed ¾ of its orbit around the earth and also looks like a “half moon” to us.

One revolution of the Moon around Earth takes a little over 27 days 7 hours. The Moon rotates on its axis in this same period of time, so the same face of the Moon is always presented to Earth. Over a period, a little longer than 29 days 12 hours, the Moon goes through a series of phases, in which the amount of the lighted half of the Moon we see from Earth changes. These phases are caused by the changing angle of sunlight hitting the Moon. (The period of phases is longer than the period of revolution of the Moon, because the motion of Earth around the Sun changes the angle at which the Sun’s light hits the Moon from night to night).

The solar system

Solar System is constituted by the Sun and everything that orbits the Sun, including the planets and their satellites; the dwarf planets, asteroids, and comets; and interplanetary dust and gas...

Inner planets and outer planets

Activity 5: Role play

Inner and outer planets (Teachers and learners)

Background Information

This lesson focuses on comparing and contrasting the four inner planets with the four outer planets and one dwarf planet. You will first explore the differences using Venn diagrams to establish the groupings in the Solar System. Then you will express these differences in size, temperature and composition artistically through dance and movement. Then, you will create a dance based on information gained from this lesson.

Materials

* Music

* Colourful scarves

* Books

* Posters and charts on the solar system.

* CD/cassette player

Procedure – Venn Diagrams

1. Discussion: How many planets are in our solar system? Name them. Explain that Pluto had been considered a planet, but in August 2006 it was demoted to a dwarf planet.

2. Use the bulletin board, classroom books, and research from previous lessons to complete the Venn diagrams on pages 11-12 of the Astronomer Journal. You should place the name of each planet in its appropriate location on the Venn diagram.

3. The Terrestrial Planets (or INNER PLANETS) have compact and rocky surfaces and the Gaseous Planets (or OUTER PLANETS) have a gaseous composition.

4. Look at and discuss the differences between the four inner planets, the four outer planets and dwarf planet.

a) Size: Inner - small Outer - big (excluding Pluto)

b) Temperature: Inner - hot Outer – cold

c) Composition: Inner - rocky Outer – gaseous (excluding Pluto)

Procedure – Interpretive Dance

1. Remain sitting after discussion and demonstrate a small movement with your hand, then a big movement with your hand. Repeat with head, then shoulders, foot, elbow, etc. staying in your own personal/self space.

2. Next, move with small and big movements while travelling around the room in general/shared space. Emphasize NO TOUCHING OR BUMPING!!! Encourage movement on different levels (high, middle, low).

3. Teacher calls out, “Inner Planets” and the dancers respond by dancing with SMALL movements. Then, Teacher calls out, “Outer Planets” and the dancers respond with BIG movements. Teacher continues to alternate between “Inner and Outer Planets”.

4. BIG/SMALL DANCE - Divide the class into small groups so you can watch each other. One group at a time dances while the other groups watch as audience members. Dancers begin in a frozen shape and begin moving when the music starts. Dancers should move either small or big in correspondence to what the teacher calls out (alternating between “Inner” and “Outer” Planets). When music stops, learners freeze in a SMALL or BIG shape.

5. Across the Floor Exercise - Identify one wall as the SUN and the opposite wall as furthest outer planet.

6. Review the order of the planets. Divide class into groups (size dependent on size of dance space). With music, one group at a time begins on one side of the room and moves to the other side of the room, changing the size of their movement (SMALL or BIG) representing the size of each planet they pass through along the way. Repeat travelling the other way. Try again, this time incorporating temperature changes that correspond with the planets.

7. ROCKY vs GASEOUS - Two groups dance at a time. Group One - OUTER

8. PLANETS - dances with light, flowing movement, demonstrating the composition of the outer planets, using scarves as a prop. Group Two - INNER PLANETS - dances with strong, hard, rocky, abrupt movement, demonstrating the composition of the inner planets. Drums or rhythm sticks may be used by the dancers as a prop.

9. Culminating Activity - Divide the class into small groups. Based on the previous activities, each group must work together to create its own dance about the Solar System’s Inner and Outer Planets. Each group must display a clear beginning, middle and end to their dance and must contain at least one or two elements from the lesson. After working for 10-15 minutes in small groups, have each group perform their dance for the other groups. Remind the groups which are watching to be a good, respectful audience by sitting quietly without talking, laughing or playing around and to be encouraging to your classmates.

Expected Results & Explanations

Upon completion of this activity, you should understand that the 8 planets can be categorised into 2 groups quite easily. You should notice that Pluto does not fall into either of these categories. Instead, Pluto may be the first of many dwarf planets.

In our Solar System, astronomers often divide the planets into two groups — the inner planets and the outer planets. The inner planets are closer to the Sun and are smaller and rockier. The outer planets are further away, larger and made up mostly of gas.

The inner planets (in order of distance from the sun, closest to furthest) are Mercury, Venus, Earth and Mars. After an asteroid belt come the outer planets, Jupiter, Saturn, Uranus and Neptune. The interesting thing is, in some other planetary systems discovered, the gas giants are actually quite close to the sun.

This makes predicting how our Solar System formed an interesting exercise for astronomers. Conventional wisdom is that the young Sun blew the gases into the outer fringes of the Solar System and that is why there are such large gas giants there. However, some extrasolar systems have “hot Jupiters” that orbit close to their Sun.

The Inner Planets

The four inner planets are called terrestrial planets because their surfaces are solid (and, as the name implies, somewhat similar to Earth — although the term can be misleading because each of the four has vastly different environments). They’re made up mostly of heavy metals such as iron and nickel, and have either no moons or few moons. Below are brief descriptions of each of these planets based on this information from National Aeronautic and Space Authority of the USA (NASA).

Mercury

Mercury is the smallest planet in our Solar System and also the closest. It rotates slowly (59 Earth days) relative to the time it takes to rotate around the sun (88 days). The planet has no moons, but has a tenuous atmosphere (exosphere) containing oxygen, sodium, hydrogen, helium and potassium. The NASA MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) spacecraft is currently orbiting the planet.

Venus

Venus was once considered a twin planet to Earth, until astronomers discovered its surface is at a lead-melting temperature of 900 degrees Fahrenheit (480 degrees Celsius). The planet is also a slow rotator, with a 243-day long Venusian day and an orbit around the sun at 225 days. Its atmosphere is thick and contains carbon dioxide and nitrogen. The planet has no rings or moons and is currently being visited by the European Space Agency’s Venus Express spacecraft.

Earth

Earth is the only planet with life as we know it, but astronomers have found some nearly Earth-sized planets outside of our solar system in what could be habitable regions of their respective stars. It contains an atmosphere of nitrogen and oxygen, and has one moon and no rings. Many spacecraft circle our planet to provide telecommunications, weather information and other services.

Mars

Mars is a planet under intense study because it shows signs of liquid water flowing on its surface in the ancient past. Today, however, its atmosphere is a wispy mix of carbon dioxide, nitrogen and argon. It has two tiny moons (Phobos and Deimos) and no rings. A Mars day is slightly longer than 24 Earth hours and it takes the planet about 687 Earth days to circle the Sun. There’s a small fleet of orbiters and rovers at Mars right now, including the large NASA Curiosity rover that landed in 2012.

The Outer Planets

Sometimes called Jovian planets or gas giants are huge planets swaddled in gas. They all have rings and all of plenty of moons each. Despite their size, only two of them are visible without telescopes: Jupiter and Saturn. Uranus and Neptune were the first planets discovered since antiquity, and showed astronomers the solar system was bigger than previously thought. Below are brief descriptions of each of these planets based on this information from NASA.

Uranus was first discovered by William Herschel in 1781. The planet’s day takes about 17 Earth hours and one orbit around the Sun takes 84 Earth years. Its mass contains water, methane, ammonia, hydrogen and helium surrounding a rocky core. It has dozens of moons and a faint ring system. There are no spacecraft slated to visit Uranus right now; the last visitor was Voyager 2 in 1986.

Jupiter

Jupiter is the largest planet in our Solar System and spins very rapidly (10 Earth hours) relative to its orbit of the sun (12 Earth years). Its thick atmosphere is mostly made up of hydrogen and helium, perhaps surrounding a terrestrial core that is about Earth’s size. The planet has dozens of moons, some faint rings and a Great Red Spot, a raging storm happening for the past 400 years at least (since we were able to view it through telescopes). NASA’s Juno spacecraft is en route and will visit there in 2016.

Saturn

Saturn is best known for its prominent ring system, seven known rings with well-defined divisions and gaps between them. How the rings got there is one subject under investigation. It also has dozens of moons. Its atmosphere is mostly hydrogen and helium, and it also rotates quickly (10.7 Earth hours) relative to its time to circle the Sun (29 Earth years). Saturn is currently being visited by the Cassini spacecraft, which will fly closer to the planet’s rings in the coming years.

Uranus

Neptune

Neptune is a distant planet that contains water, ammonia, methane, hydrogen and helium and a possible Earth-sized core. It has more than a dozen moons and six rings. The only spacecraft to ever visit it was NASA’s Voyager 2 in 1989.

Comets

Activity 6

Learn about comets

Read notes below, they talk about comets. Understand them and answer the following questions:

* What is a comet?

* What happens when a comet is heated by the sun?

* How ancient people were considering comets?

Comet, small icy body in space that sheds gas and dust. Like rocky asteroids, icy comets are ancient objects left over from the formation of the solar system about 4.6 billion years ago. Some comets can be seen from Earth with the unaided eye.

Comets typically have highly elliptical (oval-shaped), off-centre orbits that swing near the Sun. When a comet is heated by the Sun, some of the ice on the comet’s surface turns into gas directly without melting. The gas and dust freed from the ice can create a cloud (coma) around the body (nucleus) of the comet. More gas and dust erupt from cracks in the comet’s dark crust. High-energy charged particles emitted by the Sun, called the solar wind, can carry the gas and dust away from the comet as a long tail that streams into space. Gas in the tail becomes ionized and glows as bluish plasma, while dust in the tail is lit by sunlight and looks yellowish. This distinctive visible tail is the origin of the word comet, which comes from Greek words meaning “long-haired star.”

Humans have observed comets since prehistoric times. Comets were long regarded as supernatural warnings of calamity or signs of important events. Astronomers and planetary scientists now study comets for clues to the chemical makeup and early history of the solar system, since comets have been in the deep-freeze of outer space for billions of years. Materials in comets may have played a major role in the formation of Earth and the origin of life. Catastrophic impacts by comets may also have affected the history of life on Earth, and they still pose a threat to humans.

Meteorites

Activity 7

Learn about meteorites

Read notes below, they talk about meteorites. Understand them and answer the following questions:

* What is a meteorite?

* In how many types meteorites found on the earth are classified and this classification depends on what?

* Recent studies suggest that meteorites are from where and how was it done?

* Give a summary of what you have read on this topic.

A meteorite is a rock from outer space; it’s a piece of rock that has reached Earth from outer space. It can also be defined as a fiery mass of rock from space, a mass of rock from space that burns up after entering the Earth’s atmosphere.

Meteorite, meteor that reaches the surface of Earth or of another planet before it is entirely consumed. Meteorites found on Earth are classified into types, depending on their composition: irons, those composed chiefly of iron, a small percentage of nickel, and traces of other metals such as cobalt; stones, stony meteors consisting of silicates; and stony irons, containing varying proportions of both iron and stone.

Although most meteorites are now believed to be fragments of asteroids or comets, recent geochemical studies have shown that a few Antarctic stones came from the Moon and Mars, from which they presumably were ejected by the explosive impact of asteroids. Asteroids themselves are fragments of planetesimals, formed some 4.6 billion years ago, while Earth was forming. Irons are thought to represent the cores of planetesimals, and stones (other than the aforementioned Antarctic ones) the crust. Meteorites generally have a pitted surface and fused, charred crust. A meteorite that landed in Texas in 1998 was found to have water trapped in its rock crystals. The discovery helped scientists theorize about whether water exists in other parts of the solar system.

Large meteorites strike Earth with tremendous impact, creating huge craters. The largest known meteorite, estimated to weigh about 60 metric tons, is situated at Hoba West near Grootfontein, Namibia. The next largest, weighing more than 31 metric tons, is the Ahnighito (the Tent); it was discovered, along

with two smaller meteorites, in 1894 near Perlernerit (Cape York), Greenland, by American explorer Robert Edwin Peary. Composed chiefly of iron, the three masses had long been used by the Inuit as a source of metal for the manufacture of knives and other weapons. Peary brought the Ahnighito to the United States, and it is now on display at the American Museum of Natural History in New York City. The three largest known impact structures are located in Vredefort, South Africa; Sudbury, Canada (north of Lake Huron); and off the coast of the Yucatán Peninsula of Mexico. The original craters from these impacts have eroded away, but the remaining structures indicate that they were all about 300 km (about 190 mi) in diammeter.

On the figure 12.9, collisions between the planet Mars and asteroids have blasted chunks of the planet into space. Occasionally, a piece of Mars will strike the Earth, as this meteorite did about 13,000 years ago. Astronomers believe that this meteorite, called ALH84001, was blasted off of Mars about 16 million years ago.

Asteroids

Activity 8

Learn about asteroids

Read notes below, they talk about asteroids. Understand them and answer the following questions:

* What is an asteroid?

* What is the range of the size of asteroids?

* Give a summary about what you read.

Asteroid, small rocky or metallic body that orbits the Sun. Hundreds of thousands of asteroids exist in the solar system. Asteroids range in size from a few metres to over 500km wide. They are generally irregular in shape and often have surfaces covered with craters. Like icy comets, asteroids are primitive objects left over from the time when the planets formed, making them of special interest to astronomers and planetary scientists.

On the figure 12.10, Asteroid Mathilde, left, is the third and the largest asteroid ever to be viewed at close range. The Near Earth Asteroid Rendezvous (NEAR) spacecraft flew by Mathilde in late June 1997. Asteroids Gaspra and Ida, centre and right, photographed by the Galileo orbiter in 1991 and 1993, respectively, are smaller and more oblong-shaped than Mathilde. The three asteroids are partially obscured by shadows.

Most asteroids are found between the orbits of the planets Mars and Jupiter in a wide region called the asteroid belt. Scientists think Jupiter’s gravity prevented rocky objects in this part of the solar system from forming into a large planet. The giant planet Jupiter’s gravity also helped throw objects out of the asteroid belt. The hundreds of thousands of asteroids now in the asteroid belt represent only a small fraction of the original population.

Thousands of asteroids have orbits that lie outside the asteroid belt. Some of these asteroids have paths that cross the orbit of Earth. Many scientists think that an asteroid that hit Earth 65 million years ago caused the extinction of the dinosaurs. Because asteroids can pose a danger to people and other life on Earth, astronomers track asteroids that come near our planet. Space scientists are also studying ways to deflect or destroy an asteroid that might strike Earth in the future.

Many scientists believe that a large asteroid or comet struck Earth about 65 million years ago, changing the Earth’s climate enough to kill off the dinosaurs.

Kepler’s laws

Activity 9

Investigating Kepler’s law of planetary motion

Materials

* Sheet of paper* Cardboard

* Pencil* Tacks

* Calculator Procedure

a) Construct an ellipse. An ellipse can easily be constructed using a pencil, two tacks, a string, a sheet of paper and a piece of cardboard. Tack the sheet of paper to the cardboard using the two tacks. Then tie the string into a loop and wrap the loop around the two tacks. Take your pencil and pull the string until the pencil and two tacks make a triangle (see diagram at the right). Then begin to trace out a path with the pencil, keeping the string wrapped tightly around the tacks. The resulting shape will be an ellipse. The two other points (represented here by the tack locations) are known as the foci of the ellipse. The motion of the pencil is the motion of the planet about an eventual position of the sun at one tack.

b) In the diagram below are the sun and the Earth turning about it. As can be observed, the areas formed when the earth is closest to the sun can be approximated as a wide but short triangle; whereas the areas formed when the earth is farthest from the sun can be approximated as a narrow but long triangle. Can we confirm that these areas can be of same size? Why?

c) The data given below are for the planetary motion. They represent, the planet, the period of rotation of the planet about the Sun, the average distance from the sun to the planet and a column with no value of the ratio of the square of the period and the cube of the average distance. Here the time is in second [s] and the distance in meter [m].

• Calculate and fill the value of the ratio of the squares of the periods to the cubes of their average distances from the sun. • Compare these ratios for the two planets (Earth and Mars).

Exercises

4. Venus is at average distance of 1.08 x 108 km from a sun. Estimate the length of the Venusian year using the fact that the earth is 1.49x108 km.

5. The planet Mars of massmdescribes around the sun of mass M, an ellipse of mean radius of orbit a = 230x106 km in 1.8 years. The satellite Deimos of mass m1 describes around the planet mars an ellipse of mean radius a1= 28x106 km in 30h. Find the mass of the planet mars, given that M = 2x1030kg and 1year is 365days.

6. We actually know fifteen satellites revolving around the planet Uranus. Let us denote the period of revolution of satellite by T and the mean distance to the centre of the planet by r. The five bigger than others have the following characteristics:

a) (i) For each satellite, calculate T2 and r3, (ii) Assume T2 = y and r3 = x. Trace the graph of y = f(x). What conclusion related to the nature of the graph can you get?

b) (i) Calculate the slope of the plotted segment. (ii) Deduce the mass of Uranus.

Stars patterns: Constellations

Activity 10

Learn about stars pattern Read notes below and do research on internet about constellations and answer the following questions:

* What is a constellation?

* Up to now how many constellations are known?

* Give a list of at least 30 constellations known.

Away from city lights on a clear, moonless night, the naked eye can see 2000-3000 stars. As you look at these stars, your mind may group them into different shapes or patterns. People of nearly every culture throughout history have looked at the stars and given names to shapes they saw, they even invented stories to go with them. The pattern that the Greeks named Orion, the hunter, was also seen by the ancient Chinese who saw it as a supreme warrior named Shen. The Chemehuevi Native Americans of the California desert saw the same group of stars as a line of three sure-footed mountain sheep.

The patterns of stars seen in the sky are usually called constellations, although more accurately, a group of stars that forms a pattern in the sky is called an asterism. Astronomers use the term constellation to refer to an area of the sky.

The International Astronomical Union (IAU) divides the sky into 88 official constellations with exact boundaries, so that every place in the sky belongs within a constellation. Most of the constellations in the northern hemisphere are based on the constellations invented by the ancient Greeks, while most in the southern hemisphere are based on names given to them by seventeenth century European explorers.

Thus, any given point in a celestial coordinate system can unambiguously be assigned to a constellation. It is usual in astronomy to give the constellation in which a given object is found along with its coordinates in order to convey a rough idea in which part of the sky it is located. For example, saying the Crab Nebula is in Taurus immediately conveys it is close to the ecliptic and best observable in winter.

Celestial coordinates

A basic requirement for studying the heavens is determining where in the sky things are. To specify sky positions, astronomers have developed several coordinate systems. Each uses a coordinate grid projected on the Celestial Sphere, in analogy to the Geographic coordinate system used on the surface of the Earth. The coordinate systems differ only in their choice of the fundamental plane, which divides the sky into two equal hemispheres along a great circle. (The fundamental plane of the geographic system is the Earth’s equator). Each coordinate system is named for its choice of fundamental plane.

Equatorial coordinate system

Activity 11

Research on Equatorial coordinate system

The equatorial system is a coordinate system that is used to locate a body in the sky using declination and right ascension. Search on internet and answer the followings:

a) What is the difference between equatorial and geographic coordinates systems?

b) What is declination, right ascension?

c) The declination is in which unit? The inclination is in which unit?

d) Which correspondence is between the unit of declination and the one of right ascension?

e) Explain what you found in your research.

The Equatorial coordinate system is probably the most widely used celestial coordinate system. It is also the most closely related to the Geographic coordinate system, because they use the same fundamental plane, and the same poles. The projection of the Earth’s equator onto the celestial sphere is called the Celestial Equator. Similarly, projecting the geographic Poles onto the celestial sphere defines the North and South Celestial Poles.

Horizontal coordinates system

Activity 12

Reading and understanding about Horizontal coordinate system

Read notes below and give a summary of what you have read.

The Horizontal coordinate system uses the observer’s local horizon as the Fundamental Plane. This conveniently divides the sky into the upper hemisphere that you can see, and the lower hemisphere that you can’t (because the Earth is in the way). The pole of the upper hemisphere is called the Zenith. The zenith is a point in the sky that is directly above the observer. The pole of the lower hemisphere is called the nadir. The angle of an object above or below the horizon is called the Altitude (Alt for short). The angle of an object around the horizon (measured from the North point, toward the East) is called the Azimuth. The Horizontal Coordinate System is sometimes also called the Alt/Az Coordinate System.

Horizontal coordinates are very useful for determining the Rise and Set times of an object in the sky. When an object has Altitude = 0 degrees, it is either Rising (if its Azimuth is < 180 degrees) or Setting (if its Azimuth is > 180 degrees).

Normally, there are several celestial coordinates; we have also, the ecliptic coordinate system, the galactic coordinate system.

Activity 13

Choose the most suitable answer from the options

1. The angular distance of an object around the horizon, starting from the north, and measured eastwards around the horizon to a point on the horizon directly below the object’s location on the celestial sphere is known as the:

a) Horizon

b) Latitude

c) Longitude

d) Altitude

e) Azimuth

2. The angular distance above the celestial horizon is called the:

a) Horizon

b) Latitude

(c) Longitude

d) Altitude

e) Azimuth

3. This is a point in the sky that’s located directly above the observer

:a) Horizon

b) Latitude

c) Longitude

d) Azimuth

e) Zenith