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SCIENCE, first ESO Solar System

1. The Earth and its neighbours: Earth is not alone in space. Including the Earth, eight

planets circle, or orbit the Sun. They move around the Sun in the same direction, in elliptical orbits. This motion around the Sun is named ORBITAL MOTION.

The Earth has a moon, which moves around the Earth, but there are other moons orbiting around other planets. Together, Sun, planets, moons, form a Solar System. The Sun isn’t a planet, it is a star and it produces light and energy for the Solar System. MOONS are like planets, which orbit around other planets. The moons are fellow travellers of planets in their orbits around the Sun. PERIOD is the time taken for a planet to complete its orbit around another, for example, around the sun. The Earth’s period around the Sun is 1 year but periods are different for the other planets, look at the table below. ROTATING MOTION, all planets, moons and sun also rotate on themselves. Later on we will study all these motions. a. Numerical data about the Solar System

Relative

Diameter *

Relative Mass **

Relative distance to the Sun (AU) (***)

Orbital Period around the Sun (years)

Rotation Period

SUN 109,00 333000,00 0 ---- 25,4 days MERCURY 0,38 0,06 0,387 0,24 58,6 days VENUS 0,95 0,82 0,720 0,62 243,0 days EARTH 1 1 1 1 1 day MARS 0,53 0,11 1,52 1,88 1day, 37min JUPITER 11,20 318,00 5,20 11,86 9h 50min SATURN 9,40 95,00 9,51 29,46 10h 16min URANUS 3,98 14,60 19,1 84,01 15h 34min NEPTUNE 3,81 17,20 30,0 164,79 18h 26min EARTH MOON 0,27 0,01 385000 km 27,3 days 27,3 days

• (*) Times the Earth’s diameter, so for the Earth diameter, it is 1. The Earth diameter is

12800 km. • (**) Times the Earth’s mass, so for the Earth mass, it is 1. • (***) Times the distance from Sun to the Earth.

An Astronomical Unit is defined as the distance from the Sun to the Earth. 1 AU (Astronomical Unit) = 150.000.000 km.

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Activity 1: Use the previous table and try to do these exercises on your own.

a. Which is the biggest (mass) planet in the Solar System? b. Which is the smallest planet? c. Which is bigger, our Moon or Jupiter? d. If Earth had a mass like a marble, how many marbles would we need to have

the mass of the Sun? And to have the mass of the Moon? And to have the mass of Jupiter?

A2: Use the table on the previous page:

a. Which planet has the longest period around the Sun? And which has the shortest?

b. How does the period of the planet change when the distance to the Sun increases? Does it increase or decrease?

Using data to draw graphs

It is often useful to make graphical representation from data. First we select two magnitudes that we want to relate. For instance, we choose period and the distance to Sun from our first table and make a new table beside. Then, a point in the graph will represent the pair of values of each planet. Mathematicians represent this data on perpendicular axes (x, y). Horizontal axis is “x” and vertical axis is “y”. So:

  x    Relative  

distance,  to  the  Sun  (AU)  

y    Orbital  Period,  (years)  

SUN   0 0  MERCURY 0,387 0,24

VENUS 0,720 0,62 EARTH 1 1 MARS 1,52 1,88

JUPITER 5,20 11,86 SATURN 9,51 29,46 URANUS 19,1 84,01 NEPTUNE 30,0 164,79

EAR

TH

Neptune

Uranus

Saturn Jupiter

SUN

EA

RT

H

“y” Period (years)

“x” Distance (AU)

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Later we will learn more about graphs, but now we’ll start drawing conclusions from graphs. A3: A graph gives more information than a table:

a. On the graph, check the values on both axis of Uranus’ dot. Compare these values with Uranus’ pair of values on the last table.

b. If there was a planet orbiting around the Sun 25 AU away, what would its period be?

c. At what distance is an imaginary planet with a period of 60 years orbiting? A4: Let us make a scale model of the Earth, Moon and Sun.

a. If we take 1cm for the diameter of the Earth, what diameter do the Sun and moon have?

b. Is it easy to represent this model using clay? A5: Use a book or do online search to find out, which planets are solid and which are gaseous. After that, using the table on page 1, look for other differences between the rocky planets and the gaseous ones. A6: What do Inner Planets or Outer Planets mean? Name them. A7: How do you get a body to move around you? How does the Sun get the planets to move around it?

b. Meteoroids, asteroids and comets: i. Meteoroids are small bodies, the biggest of them having less than 50 meters

across. Meteoroids are solids. When some of them collide with the Earth we call that a meteor. The visible light from the sky is the result of heat as it enters a planet’s atmosphere. Often we call this phenomenon “falling stars or shooting star”.

ii. Asteroid: It is is a rocky body, smaller than a planet and bigger than a meteoroid. It is made of metals or carbonates. They move around the Sun. In the Solar System, most of them are moving in orbits between Mars and Jupiter, and are called Asteroid Belt.

iii. Comet: It is made of ice and it is a small body in the

Solar System. When passing close to the Sun, it displays a visible atmosphere (or coma) and sometimes also a tail. This phenomenon is due to the solar energy, the heat makes the ice and small particles of dust evaporate. Comets are orbiting around the Sun. Comet Hale-Bopp 1997

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2. Light:

a. Light from the sun or others sources travels in straight lines but when a light ray

hits an object part of this light is bounced off, it is call reflection. This reflected light allows us to see objects. So, we cannot see any object, at room temperature, without an external source of light. In a dark room we cannot see anything. There are two kinds of reflection:

a. Diffused reflection: When light strikes the surface of an object it bounces in all directions. This reflection is the most common and it is the one that allows us to see any body from different positions.

On the left image, light rays are represented emerging from only two points on this man, the pipe and his coat. Each point reflects light in all directions, so we can see him from any position.

b. Specular reflection (mirror – like): Light reflected from a surface into a single outgoing direction, if light comes from a single direction.

Object Both eyes can see the object, because of the

diffuse reflection of incident light

Light

Light This eye

sees light

This eye doesn’t see light

The law for specular reflection: The angle at which the light strikes the mirror, or other reflective surface, is called the incident angle. The angle of the reflected light ray is called reflected angle. The law of reflection states that the incident angle equals the reflected angle.

i = i’

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b. How is light produced? All bodies emit and absorb radiations (Energy, like waves in water). The type of radiation and the rate at which an object radiates energy depends on its temperature. When an object increases its temperature, when we switch on an electric stove, our eyes can see part of its radiation, this is what we call LIGHT (visible). From about 525ºC and up all bodies emit visible radiation. The temperature of the Sun’s surface is about 6000 degrees; its radiations and light give energy for plants and keep our planet warm. So, light is radiation coming from a body that our eyes can see. But there are many more types of radiation that we can’t see. For example, can you see the radiation coming from your TV remote control when you push “on”? Can you see the radiation from your friend in a dark room?

Nowadays we don’t need to have a body at high temperature to get light, science has provided easier ways. We will study how we produce light in following years.

c. All radiation, including light, moves faster than anything else in space. Its speed is 300.000 km/s. So, light moves in all directions at this speed and travels in straight lines from the Sun or any other source of light.

d. Shadow and penumbra: Let us play with light. All we need is a dark room, a light source and a white wall. We also need somebody to stop the light before the light beam reaches the wall and produces a shadow. Perhaps, shadows are not something new for you, but what about penumbra?

A8: Which of these images, “ A, B or C”, represents how we can see the tree.

Arrows represent the direction of light rays.

A B C

It is very important to understand the difference between reflected light and radiated light from the object.

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A9: Will the eye detect the light ray that strikes the mirror? Why? A10: Study of electric heater radiation:

a. Turn on the electric heater and, at the same time, put your hand close to it without touching it. Can you feel its radiation? At first, can you see its radiation?

b. A few seconds later, can you see its radiation? Why can you see and feel its radiation now?

A11: The speed of light is 300.000 km/s; it means that light runs 300.000 km in 1 second and 600.000 km in 2 seconds, etc. Use the data on the table on page one, to find the distance between Sun and Earth and calculate how long it takes a light ray to reach Earth from the Sun. How long does it take a light ray to reach Saturn from the Sun? Investigation Let us investigate when and how the penumbra is produced.

i. Use the fact that light travels in straight lines to explain how the shadow is produced.

ii. What is penumbra? iii. Use two kinds of light source, one of them a big source and another that emits

lights only from a single point. Now, study the shadows again. iv. Conclusions:

Shadow is produced … The penumbra is produced when …

Mirror

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3. Day and night on planets and moons. Rotating motion.

a. At any time, half of any planet is facing the Sun: It is daytime. The other half

is away from the Sun: It is nigh time.

b. Spinning motion of planets. All the planets, moons and Sun are rotating around their own imaginary axis. This motion produces days and nights on any planet or moon. Our planet rotates around its imaginary axis that crosses the Earth passing through the north and south poles. Earth rotates from the west to the east, so we see the Sun rising from the east side and setting in the west. The Earth completes a 360º rotation in rotates in 23 hours, 56 minutes and 4,1 seconds, almost 24 hours, 1 day.

SUN

This side is daytime This side

is nigh time

EARTH

Earth Axis

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4. The Earth’s yearly journey around the sun. The

seasons. Sun position, through the day, in the sky.

a. The Earth orbits around the Sun taking 365 days. The Earth rotates 365 times around its own axis while completing its orbit around the Sun.

b. The Earth does not spin upright, its axis is tilted 23,45º and always remains constant and parallel in its motion around the Sun. This last property is common to all the planets, moons and stars.

This image shows the Earth’s motion around the Sun with the Earth’s axis remaining parallel in its orbit.

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A10: This new image shows the Earth from both sides around the Sun. On the right side of the image, the northern hemisphere “A”, is tilted towards the Sun and the southern hemisphere of the Earth, “B” is tilted away from the Sun. On the left side of the image we have the opposite situation:

a. In Which position does the northern hemisphere receive more radiation coming from the sun? On which hemisphere do light rays reach the surface more perpendicularly?

b. Choose the position that represents Summer and Winter in the northern hemisphere.

c. Choose the position that represents Summer in the southern hemisphere? Could it be Summer in both hemispheres at the same time?

d. Choose the positions that would represent the months of June and December for the northern hemisphere.

e. Do the Sun’s rays reach the North Pole in Winter? Will we see the sunrise in Winter in the North Pole? What happens on Summer?

f. Draw the position for the Earth’s axis during Autumn or Spring

B B

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c. Relative motion of the Sun in the sky seen from Earth through the day.

Because the Earth’s axis is tilted and it moves around the Sun, we do not see the sun’s position in the sky in the same way. In the Winter the sun appears nearest to the horizon and in the Summer, it is higher, as it is shown in the next picture.

Solar Noon is the sun highest elevation in the sky, it is 12 o’clock solar time at any day of the year. The local time depends on energy we want to save through use of natural daylight. In Spain the official time is 2 hours past solar time in summer and 1 hour past in winter in order to save energy.

A10. Study of shadows: • At what solar daytime is the

length of a shadow shortest? • When is it shorter, in Summer or

in Winter? • When is the shortest shadow

produced along the year? • When is the longest shadow at

the Solar Noon time produced?

SOLAR NOON

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5. Our Moon, Phases of the Moon.

Our Moon moves around the Earth and takes 27,3 days to complete its orbit. The Moon is also spinning on its own axis and takes 27,3 days in its rotating motion, the same time as its orbital motion. As a result, from the Earth, we always see the same face of the Moon. The Moon is the Earth’s companion in space; it is located about 384.000 km away. When the astronauts landed on the Moon in 1969, they found that a fine white dust covered its surface. Because there is no wind and it never rains or snows, the dust never moves and nothing change, a footprint on the Moon will remain for millions of years. The Moon is the biggest, brightest object in the night sky. Moon reflects the sunlight on its surface and that is the light that arrives to the Earth and we can see.

a. The plane of Moon’s orbit is tilted 5º from the plane of Earth’s orbit around the Sun. This tilt remains constant and parallel always in its orbit. As shown in this image:

So, a lot of time the Moon is over or under the Earth’s orbit plane. The plane of the Earth’s orbit is called ecliptic plane.

A11. True or false:

a. It is only possible to see the Moon at night. b. We can see the Moon every night. c. We can see the Moon all night.

A12. Where is the Moon when we can’t see it?

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d. Lunar Phases All that can be seen from the Moon on the Earth is its brightly lit, sunny side. As it circles (moves around) the Earth, the sunny side of the Moon is seen from different angles and so it seems to change shape.

• When we cannot see the Moon it is called New Moon. • For the next two coming weeks, the bright side part gradually

increases until we see the Full Moon. • For the last two weeks, the bright decreases part of the Moon until

returning to New Moon.

A13. True or false:

a. The Moon is not rigid and changes its shapes when are moving around the Earth.

b. The Moon receives different rates of sunlight when it is moving around the Earth.

c. All we can see from the Moon depends on the relative position of Moon, Sun and Earth.

Investigation: Let’s reproduce Lunar Phases in the lab. What will we need?

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6. Eclipses.

During their orbital motion around the Sun, the Earth and the Moon can sometimes lie on the same straight line. In this situation the Earth or the Moon stop the light from sun and produce shadow over the other.

Above we can see a Lunar Eclipse, which occurs when the Moon passes directly behind the Earth into its umbra (shadow). The Earth is between the Sun and the Moon. Below, the Moon is between the Sun and the Earth, this is a Solar Eclipse. It depends on where you are on Earth, the Sun would be fully obscured by the Moon, umbra (shadow), this is a Total Eclipse. In other places on Earth you can see only a part of the Sun, Partial Eclipse, penumbra. But, in the most part of the Earth you see the entire Sun shining.

NOT TO SCALE

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Why aren’t there Solar and Lunar eclipses every month? Because the plane of the moon orbit around the Earth is tilted 5º to the plane of Earth’s orbit around the Sun. So, when the Moon is between the Sun and the Earth, the most times it is under o above the Earth’s plane orbit, and it doesn’t cast shadow on the Earth.