P7 Physics ‘triple science’ Route map Over the next 24 lessons you will study: Friday 21 October 2011 P7.1 What is a telescope P7.2 Describing lenses P7.3 Refracting telescopes P7.4 Reflecting telescopes P7.5 Radio telescopes P7.7 Images of stars P7.8 The Sun, Moon and Earth P7.9 Observing the skies P7.10 Eclipses P7.11 Star distances P7.12 Star brightness P7.6 Ray diagrams P7.14 Galaxies-cepheid variable stars P7.15 Galaxies one or many P7.13 Star temperatures P7.16 Mapping the Milky Way P7.17 The changing Universe P7.18 Our Sun P7.19 The composition of stars P7.20 Emission spectra P7.21 Atoms and nuclei P7.22 Nuclear fusion P7.23 Behaviour of gases part one P7.24 Behaviour of gases part two P7.25 Types of stars P7.26 Structure of our Sun End of module test P7.27 Protostars P7.28 Star death
P7.8 The Sun, Moon and Earth Decide whether the following statements are true or false:
Understand the phases of the moon and its apparent motion as viewed from Earth.
Understand the difference between sidereal and solar days
We will focus on. Friday 21 October 2011 First activity: List the vents, feature objects stars planets or any other objects you can see with the naked eye either during the day or at night ? Literacy: Sun, Moon, full Moon, Gibbons Moon, crescent Moon, New Moon, Earth, phases of the moon, sidereal days, solar days, orbit, planet and rotation. Numeracy: Eclipses happen due to an amazing coincidence, the moon is 400 times smaller than the sun, which is 400 times as far away, so the moon will perfectly cover the sun when viewed from Earth ! PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers
Extension questions: 1: How long does it take the moon to complete one full orbit of the Earth ? 2: Why does the appearance of the Moon viewed from Earth appear to change and go through different phases each month ? 3: Explain why the Sun appears to move across the sky each day ? 4: What position does the Sun, Moon and Earth need to be in to give the appearance of a new moon ? 5: Explain why we measure time according to the Sun’s movements rather than the stars movements across our sky ? Know this: a: Know the phases of the Moon. b: Know the difference between solar and sidereal days. Friday 21 October 2011 Introduction: People used to believe that the Earth was the centre of the Universe and that the Sun and planets revolved around the Earth. We now know that this is not correct and it is in fact the Earth orbiting the Sun and the Earth revolving on its own axis that cause the appearance of objects in the universe moving around the Earth. The Moon when viewed from Earth appears to move across the sky, but it is actually orbit the Earth once every 28 days. During its orbbit around the Earth, it also appears to change its appearance, going through a series of ‘phases’, from ‘full moon’ to ‘crescent moon’ to ‘new moon’. P7.8 The Sun, Moon and Earth
Look at the photograph and information and answer all the questions: A lunar eclipse is when the Earth is in between the Sun and the moon. During the eclipse, the moon takes on a reddish appearance, because red light from the Sun’s rays are refracted around the Earth’s surface. A solar eclipse is when the moon is in between the Sun and the Earth. The last total eclipse visible in England was on August 11 th 1999. During a solar eclipse, the surface temperature drops, birds roost and you can see the stars near the Sun. Explain why we only see one side of the moon, here from Earth ? Waning crescent Waxing crescent Full Moon Waning gibbous Waxing gibbous Last quarter First quarter New moon Key concepts How do we describe the moon when it cannot be seen from Earth ? The moon’s gravitational pull causes what event here on Earth twice daily ? P7.8 a
Look at the photograph and information and answer all the questions: After spending billions of dollars developing the Apollo mission rockets, Apollo 11 carried the ‘Eagle’ lunar module to the surface of the moon. On July 20 th 1969, Neil Armstrong landed on the surface of the moon. Many more successful missions (except Apollo 13) continued to study our own satellite until funding was stopped and the Apollo rockets were replaced by the reusable space shuttle Who was the second man to set foot on the lunar surface after Neil Armstrong ? Which Apollo lunar mission suffered an in-flight explosion and was portrayed by a Hollywood film ? Lunar rock samples taken from the Moon’s surface were dated as the same age as rocks from Earth...what does this tell us ? Key concepts P7.8 b
Key concepts Look at the photograph and information and answer all the questions: Why is the surface of the moon good evidence that the Earth was hit by many asteroids in its past ? The moon’s surface is covered in craters, which element would you find around these cater impact sites ? The moon, devoid of an atmosphere, surface running water and a molten core does not have a rock cycle and therefore no rock weathering processes. Craters formed by colliding asteroids are perfectly preserved over millions of years. Looking at the moon’s surface you can begin to appreciate that the moon and the Earth must have been hit many thousands of times by incoming asteroids of various sizes. Could one of these impacts in our own history have cause the mass extinction of dinosaurs and other species about 65 million years ago ? Craters found on the Moon's surface P7.8 c
Key concepts P7.8 d Look at the photograph and information and answer all the questions: The picture above shows the path taken across our sky during a winter's day. How might the sun’s path differ if this photo was taken on a summer’s day ? What happens to the length of day light hour as you move form summer, autumn, winter, spring and summer again and why ? If you observe the path of the Sun, it rises in the east and then moves to a high point at noon and then sets in the west. It looks like the sun is moving around the Earth, however, this path is caused by Earth spinning on its own axis once a day. In the summer, the sun rises earlier sets later and rises higher in the summer sky.
Look at the photograph and information and answer all the questions: Earth is actually tilted 23.5° relative to it's orbit around the Sun. This slight tilt is the cause of the seasons. During the summer, in the northern hemisphere, the northern hemisphere is tilted towards the Sun. During the winter, the northern hemisphere is tilted away from the Sun. Therefore in winter, less solar energy is received causing cool winter temperatures and short daylight hours. Explain why in the summer, the North Pole is in constant daylight and in the winter it is in constant darkness ? During the year, there are two equinoxes, the winter solstice (Dec. 21 st ) and the summer solstice (June 21 st |)....describe what is unique about these two days ? Explain why there is no winter or summer on the Equator ? Key concepts P7.8 e
Key concepts Look at the photograph and information and answer all the questions: midnight midday midnight midday P7.8 f Sidereal and solar days Star seen at 23h 56min Star seen at midnight How long is a day ? An Earth day is the time it takes for the sun to cross the sky and appear again in the same place. This takes 24 hours and is called solar day. We could chose to measure the length of time it takes for the earth to complete exactly one spin around its own axis, this is slightly shorter at 23h and 56m. This is called a sidereal day. Why do you think we have chosen to use the ‘solar day’ rather than the ‘sidereal day’ length on our clocks? Why is a solar day 4 minutes longer than a sidereal day?
P7.8 Plenary Lesson summary: Earth shadow lunar phases Friday 21 October 2011 The Moon has eight distinct phases but it also plays other roles from controlling the Earth’s ocean tides and how this tidal water movement can affect our daily lives here in the UK and the habitat of many animal and plant species that live on or close to tidal areas. At the time of a full Moon, more 999 calls are made and more people are sanctioned under the mental health act...spooky ! How Science Works: Research into mapping the sky at night and the star constellations such as Pieces, Aries e.t.c. Look into the movement of planets like Mercury, Venus and Mars across the night sky. Preparing for the next lesson: The Moon takes 28 days to complete one orbit of the ________. This is a lunar month. Each _________ month the Moon’s appearance changes, causing the _________ of the Moon. This is caused by an observer on the Earth either seeing the illuminated side of the Moon or the side that is in __________. Decide whether the following statements are true or false : False True 3: The Earth orbits the Moon once every 26 days ? False True 2: The Sun takes 24 hours to cross the sky and appear again in the same place ? False True 1: A solar day is shorter than a sidereal day ?
P7.9 Observing the skies Decide whether the following statements are true or false:
Understand how the movement of the Earth affects the apparent motion of the stars.
Understand that when viewed from Earth, planets appear to move against a fixed background of stars and understand the retrograde motion of mars.
We will focus on. Friday 21 October 2011 First activity: Name three planet sand three stars that you can see in the night sky ? Although stars change their positions over a 12 month cycle one star doesn’t and was used to navigate by sailors in the 17 th , 18 th and 19 th centuries. Name that star ? Literacy: Night sky, stars, Milky Way, Polar star, planet, constellation, retrograde motion, northern hemisphere, southern hemisphere, Mercury, Venus and Saturn. Numeracy: On the planet Venus its day is longer than its year ! Each day on Venus (time to spin once on its axis) takes 243 Earth days. A year (time to orbit the Sun) on Venus takes 224.7 Earth days. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers
Extension questions: 1: Name three star constellations other than the one written above ? 2: Explain why the pole star was used (before GPS) to navigate around the globe ? 3: Why can you not use the pole star to navigate during the day ? 4: In the night sky, how can you tell a planet like Venus from a star ? 5: Do people in the southern hemisphere see the same star constellations as people who live in the northern hemisphere ? Know this: a: Know how the movement of the Earth affects the apparent motion of star in the night sky b: Know the movement of planets view from Earth Friday 21 October 2011 Introduction: Look up at the day or night and you will see by just using your eyesight many features including the twelve star constellations (Aries, Cancer, Gemini e.t.c), the pole star used by sailors to navigate and occasionally the odd comet and meteorite. A constellation is a group of star that form a pattern in the night sky. The constellations on view change through the winter and summer months as the Earth orbits the sun. In the night sky we cal also see five different planets by those planets reflecting light from the Sun. They move slowly relative to the stars and include Mercury, Venus, Mars , Jupiter and Saturn P7.9 Observing the skies
Key concepts P7.9 a Look at the photograph and information and answer all the questions: In September give three constellations that you cannot see in the night sky In January give three constellations you cannot see in the night sky ? Astronomers can identify stars by stating what constellation they belong to. Orion (the hunter) is one of the most famous and easiest to spot. The night sky appears to change through out the year. This is because the earth is moving around the sun. You will be able to see the constellations in different position in the summer than in the winter. Explain why the constellations appear in different position in the night sky throughout the year?
Key concepts P7.9 b Look at the photograph and information and answer all the questions: Explain why navigators first look for the plough or big dipper before trying to locate the pole star ? By measuring the angle between the horizon (flat) and the pole star using a sextant (like a protractor) what information could this tell you ? The pole star or Polaris, is a prominent bright star in the night sky. That is not why it is unique. It is unique because its is aligned exactly with the Earth's axis of rotation; that is, a star whose apparent position is the same, when viewed from the Earth's North Pole. It is therefore used to show which way is north at night by sailors before the days of GPS. Using the pole star to navigate Pole star Pole star Big dipper (the plough) North
Key concepts P7.9 c Look at the photograph and information and answer all the questions: Explain when looking at the night sky how you can tell the difference between seeing a planet and star ? Explain why we cannot see other planets like Neptune and Uranus in our night sky ? Mercury, Venus and Saturn in the night sky Mercury Venus Saturn 20 th Oct 19 th Nov 10 th Oct 5 th Nov 10 th Oct 19 th Nov The five brightest planets - Mercury, Venus, Mars, Jupiter and Saturn - have been known since ancient times and can easily be seen with the naked The planets can be distinguished from the stars because their position changes slightly against the background stars from one night to the next, and their brightness varies in a regular cycle over a period of time. Stars are so distant that they appear as points of light in the night sky, and they appear to twinkle because of turbulence in the Earth's atmosphere
P7.9 Plenary Lesson summary: chart year heavens plough Friday 21 October 2011 The patterns of the star constellations always stay the same, but during the course of the night they move across the sky from East to West. This is because the Earth is rotating on its axis. From season to season you see different constellations in the sky. This is because the Earth is moving around the Sun on its year 365 day orbit. How Science Works: Research into both solar and lunar eclipse, why they happen and how often they happen Preparing for the next lesson: The best way of finding your way around the _________ is by using a star _______. By picking the more familiar constellations you can use these as pointers to other constellations. If you are viewing from the northern hemisphere one of the best places to start is with the __________. The Plough is visible all ______ round. Decide whether the following statements are true or false : False True 3: You can see five planets including Uranus from Earth ? False True 2: The pole star is a star that stay in the same position through a Earth year ? False True 1: There are 13 constellations, for example Aries visible in the night sky ?
P7.10 Eclipses Decide whether the following statements are true or false:
Understand why solar and lunar eclipses happen
Understand the effect of the moon’s tilted orbit on the frequency of eclipses
We will focus on. Friday 21 October 2011 First activity: During a full solar eclipse, explain why scientists can see stars in the region where the sun is for only a brief period of time and explain why astronomers can also study the anatomy of the sun’s corona ? Literacy: Lunar eclipse, solar eclipse, umbra, penumbra, annular eclipse, total eclipse, corona, tilted, orbit, frequency, moon, earth and sun. Numeracy: The surface of the sun is hot, about 5500 °C but the corona is much hotter at about 1.5 million °C! . Scientists can discover details of the Sun’s corona during an full solar eclipse. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers
Extension questions: 1: Why are lunar eclipses more frequent than solar eclipses ? 2: During a solar eclipse what happens to a) the day time temperature and b) birds ? 3: What's the average duration of a solar eclipse, 7.5 minutes or 1 hour ? 4: Explain what happens to a) birds and b) nocturnal animals during a solar eclipse ? 5: Explian why you can see the sun’s corona during a solar eclipse ? Know this: a: Know why solar and lunar eclipse happen b: Know the effect of the Moon’s tilted orbit on the frequency of lunar eclipses Friday 21 October 2011 Introduction: Eclipses involve both the Sun, Moon and the Earth. Both lunar and solar eclipses are relatively rare, however when they happen can be calculated by astronomers. In a solar eclipse, the Moon blocks the Sun’s light falling on Earth’s surface In a lunar eclipse, the Moon moves into the Earth’s shadow and block light falling on the Moon’s surface. The fact that the Moon precisely blocks the Sun’s rays relies on remarkable coincidence, they appear the same size in the sky ! P7.10 Eclipses
Key concepts P7.10 a Look at the photograph and information and answer all the questions: Explain why a lunar eclipse only occurs during a full Moon ? Explain why during a lunar eclipse the Moon takes on a reddish colour ? A lunar eclipse: The Earth’s orbit takes the Earth directly in front of the Sun’s rays which illuminate the moon. When the moon is in the Earth’s Umbra, no white sunlight can reach the moon’s surface and it is seen to appear dark red. This is because the Earth's atmosphere bends red light around the Earth which then falls and is reflected by the moon’s surface. Sunlight Sunlight Moon Moon’s orbit Earth Umbra Penumbra Penumbra
Key concepts Look at the photograph and information and answer all the questions: Look at the above diagram, how long does a lunar eclipse last for ? Explain why a lunar eclipse lasts longer than a solar eclipse ? A total lunar eclipse is an amazing sight in the night sky. The moon takes on a reddish appearance for a few minutes. This is because red light from the Sun is refracted around the Earth by the Earth’s atmosphere. The Atmosphere acts like a lens bending red light. At 23.38 (left picture) the moon is almost in total darkness. During totality, red light illuminates the moon’s surface. P7.10 b 23.38 01.44 21.26
Key concepts Look at the photograph and information and answer all the questions: A solar eclipse: The moon’s orbit takes the moon directly in front of the Sun’s rays which illuminates the Earth. Observers in the Western hemisphere see the moon’s shadow move across the surface of the Earth. When the Earth is in the moon’s umbra, no sunlight can reach the Earth’s surface. Because the Earth rotates on its axis, the shadow moves across the Earth surface P7.10 c Explain the difference between a lunar and a solar eclipse ? When viewing a solar eclipse, what should you never do ? Sunlight Sunlight Moon Penumbra Penumbra Umbra path Umbra
Key concepts P7.10 d Look at the photograph and information and answer all the questions: Explain why when you have a solar eclipses ocean and sea tides are both higher and lower than average ? Explain how you can safely observe a full solar eclipse ? Eclipses are caused by the moon coming between the sun and the earth and blocking out the sun. As the moon orbits the earth you may think that eclipse should happen once a month, but in fact they are very rare. The reason is that the moon’s orbit is tilted by about 5 degrees so that most months the Sun, Moon and Earth do not actually perfectly line up. Earth Why are eclipses so rare Sun (not scale) Moon 5 o
Key concepts P7.10 e Look at the photograph and information and answer all the questions: A solar eclipse is when the moon is in between the Sun and the Earth. The last total eclipse visible in England was on August 11 th 1999. During a solar eclipse, the surface temperature drops, birds roost and you can see the stars in the same sky area as the Sun. These stars are normally obscured by bright sunlight during the day. Astronomers study these stars during a total eclipse. The next eclipse in Britain is on 7 th October 2135. During a total solar eclipse, what would an observer standing on the Earth’s surface see if they looked at the sun ? Will you ever be able to see this for yourself ? Work out how old you will be on the next full solar eclipse to occur in the UK ? Solar eclipses
P7.10 Plenary Lesson summary: night lunar moon red Friday 21 October 2011 It is still far more commonplace to experience a lunar eclipse. That’s because the darkened full Moon can be seen from anywhere on the night-time half of the Earth during the eclipse. To see a total solar eclipse, you have to be in the path of totality. This path, sometimes up to 200 miles wide. With fewer than 70 total eclipses per century, the chance to see one is for most of us a once-in-a-lifetime event. How Science Works: Research into how do astronomers measure the distances between Earth and stars other than our own Sun. Preparing for the next lesson: There are two basic types of eclipses ________ and solar. Most people have seen at least one lunar eclipse, when the full __________ passes through the shadow of the Earth. If you observe a lunar eclipse visible only at _____, you’ll see the bright lunar disk turn dark, sometimes a coppery ____colour Decide whether the following statements are true or false : False True 3: A lunar eclipse is where the moon block light from the sun falling on Earth ? False True 2: Air temperatures can drop as much as 20 o C during a full solar eclipse ? False True 1: The width of the moon’s shadow on Earth is about 170 miles ?
P7.11 Star distances Decide whether the following statements are true or false:
Understand how to use different methods in calculating distances between stars.
Understand the use of the parallax angle to measure the distance between earth and a star
Understand the use of parsecs and light years as units of distance.
We will focus on. Friday 21 October 2011 First activity: In time, how long do you think light takes to travel form a) the Sun to the Earth’s surface b) the Moon to the Earth’s surface c) across the entire length of the Milky way d) From our nearest galaxy Andromeda to Earth’s surface and e) from the furthest away galaxy in the known Universe to Earth ? Literacy: Universe, galaxy, solar systems, stars, distance, Parallax, light year, brightness, light year, light speed, light, parsec, time and distance. Numeracy: Light travels at 300,000 km or 300,000,000 m every second and can be used to calculate huge distances between planets like Earth and Jupiter or and stars like our sun and our nearest star, Alpha Centauri. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on generating ideas and exploring possibilities. Team workers Effective participators Self managers
Extension questions: 1: Define what a light year is and how far does light travel in a) one second and b) one week and c) one year ? 2: Which is larger a light year or a parsec and how many light years an in a single parsec ? 4: Why do scientists measure distance in light years or parsecs when dealing with objects found in our own Universe ? 5: Our nearest star (other than the sun) is about 4 light years away. Work out its distance form Earth in km and also if a space craft was sent today travelling at 25,000 km per hour how long would it take to reach that star ? Know this: a: Know how to calculate distance between planets and stars. b: Know the use of parsec and light years as unit of distance in our own Universe. Friday 21 October 2011 Introduction: Light from our own sun which is approximately 93,000,000 miles away, takes about 8.7 minutes to reach Earth. Other stars in our own galaxy and other galaxy are very distant. We can use the parallel effect to measure the distance between Earth and stars like Alpha Centauri, our near star which is two light years away (that’s 2 x 365 x 24 x 60 x 60 x 300,000 km away) The parallax effect, when the same star’s position is studied at different times of the year (as Earth moves around the Sun) allows astronomers to accurately calculate a stars distance from Earth. P7.11 Star distances
Key concepts P7.11 a Look at the photograph and information and answer all the questions: Why are scientists interested in knowing the distance between planet Earth and stars found in our own galaxy the Milky Way ? Our closet star is called Alpha Centauri which is 4.22 light years away. How old were you when light reaching now left Alpha Centauri ? Using the Parallex method, when the Earth moves form one side of the sun (June) to the other (December) every six months. When seen through a telescope based here on Earth, a nearer star will shift its position against the position of a more distant star. The nearer the star the greater the shift. Scientists can therefore work out using this method how far away each star in the night sky is from planet Earth. Calculating star distances using parallax method Earth in June Earth in Dec. star sun December Parallax angle June Parallax angle
Key concepts P7.11 b Look at the photograph and information and answer all the questions: Remember: 360 o in a full circle. 60 minutes of an arc in 1 o 60 seconds of an arc in 1’ so: 1 second = 1 parsec = 3.1 x 10 13 km or ) The nearest star in the diagram has a parallax angle of 2 seconds and is 2 x 3.1 x 10 13 km from Earth. The second star has a parallax angle of 3 seconds. Work out its distance form Earth. Using the Parallax method we can determine the distance between earth and stars in our own Milk way. A near star will have a greater parallax angle at June and December. A distant star will have less of a shift and therefore a smaller parallax angle in June and December (see above diagrams). The nearer the star the greater the shift. Scientists can therefore work out using this method how far away each star in the night sky is from planet Earth. Calculating star distances using parallax method Earth in June Earth in Dec. near star sun Earth in June Earth in Dec. sun distant star
Key concepts P7.11 c Look at the photograph and information and answer all the questions: How long would it take light to travel from Earth to the Moon and back again ? Imagine there was life on a planet orbiting our nearest star Alpha Centauri and we sent them a question at the speed of light how long would we have to wait for an answer ? Astronomers have estimated the Universe to be 155 billion light years across. By comparison, our nearest galaxy Andromeda, is two million light years away and light form the sun takes about 8.7 minutes to reach Earth. When talking about distances within the Universe, it would be no good to use meters or kilometres so we use units like light years and parsecs. Moon Pluto Andromeda Sun Distances across the Universe 8.7 minutes: Sun to Earth 0.83 seconds: Earth to Moon 2 million light years : Earth to Andromeda galaxy 4.22 Light years: Earth to Alpha Centauri 155/2 billion light years : Earth to edge of Universe 5.6 hours: Earth to Pluto
P7.11 Plenary Lesson summary: objects parallax Sun Earth Friday 21 October 2011 A simple everyday example of parallax can be seen in the dashboard of motor vehicles that use an older-style "needle" speedometer gauge. When viewed from directly in front, the speed may show exactly 60; but when viewed from the passenger seat the needle may appear to show a slightly different speed, due to the angle of viewing. How Science Works: Research into observing different stars and how astronomers measure the brightness for the stars in our own galaxy the Milky Way Preparing for the next lesson: Astronomers use the principle of _______ to measure __________ to celestial objects including to the Moon, the ______, and to stars beyond the Solar System. Recently as many as 100,000 stars in our own Milky Way have been studies and their distances from_______ are now known. Decide whether the following statements are true or false : False True 3: Light travels further during a par sec than a second ? False True 2: One light year is the distance light travels in ten years ? False True 1: Alpha Centauri is the closest star outside our own galaxy ?
P7.12 Star brightness Decide whether the following statements are true or false:
Understand that stars have different brightness according to its distance from Earth, it size and the rate of energy radiated by the star
Understand a star’s luminosity will depend on its temperature and size
We will focus on. Friday 21 October 2011 First activity: Explain for an observer what two factors will determine the actual brightness of two objects that emit light. How could you compared the brightness of 100 different light bulb making sure it is a fair test ? Numeracy: A star that is one magnitude number lower than another star is about two-and-a-half times brighter. A magnitude 3 star is 2.5 times brighter than a magnitude 4 star. A magnitude 4 star is 2.5 times brighter than a magnitude 5 star. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers Literacy: Stars, luminosity, brightness, surface temperature, distance mass, size cepheid variable star, expansion, contraction, period, distance and galaxy.
Extension questions: 1: What is the brightest object observable to humans in the sky ? 2: Explain why actual brightness does not give you a real indication of the luminosity and/or size of a star ? 3: Imagine you had two stars, A and B. Star A was twice as large as star B with twice the luminosity, but 10 times further away than star B. Which star would appear brighter from Earth ? 4: How does dust or light pollution affect our judgements on how bright stars are in the night sky ? Know this: a: Know that a star’s actual brightness is determine by its size, surface temperature and distance form Earth b: Know what factors can affect the luminosity of a star. Friday 21 October 2011 Introduction: All stars are different, they can have very different masses, sizes and surface temperatures. A real measure of a star’s brightness depends on two factors: its surface temperature and size would be to compared to a stars brightness with other stars from a fixed distance (known as one astronomical unit). This would give us the star’s absolute brightness. Another way of describing a star is by looking at its actual brightness which takes into account both the luminosity of the star and its distance form Earth. This is what we experience when we look at the night sky. P7.12 Star brightness
Key concepts P7.12 a Look at the photograph and information and answer all the questions: What two factors affect the brightness of a star from a fixed distance ? Other than the two factors you have given for question 1, what other factor affects the brightness of a star ? Look out to the night sky you may see up to 2000 different stars. Take any star constellation like Orion, you will see star with different colours and brightness levels. Scientists have two star brightness scales, which are: absolute brightness where all stars are ranked on brightness from an imaginary fixed distance from Earth and actual brightness which takes into account the star’s brightness and its distance from Earth. Star brightness in the night sky Earth
Key concepts P7.12 b Look at the photograph and information and answer all the questions: Although the Sun is 50,000 times less luminous than the star Rigel, it is the brightest object observable from Earth explain why ? Look at the values of ‘ab’ or absolute brightness for the four stars labelled in the Orion constellation, which star has the highest brightness on this scale ? ab = 2.07 Bellatrix Betelgeuse ab = -7.2 ab = 1.64 Salph Rigel ab = -8.1 Orion, also known as "The Hunter," is a constellation in the zodiac. The brightest stars in Orion are Rigel, Betelgeuse, and Bellatrix. Rigel is the brightest star in the Orion constellation, in fact in the entire night sky. Its has an absolute brightness of -8.1. It is a blue (very hot) supergiant, over 60 million miles in diameter (almost 100 times bigger than the sun). It is more than 50,000 times more luminous than the Sun. It has an actual brightness observe from earth’s surface of +0.12 because it is over 900 light-years from the Earth. Stars in Orion constellation
P7.12 Plenary Lesson summary: zero dimmer star brighter Friday 21 October 2011 Astronomers measure the brightness of stars according to a system originally devised by Hipparchus in 120 B.C. Hipparchus ranked the brightness of stars in the sky on a scale of 1 to 6 as seen from the Earth. The brightest stars he could see were classified as first magnitude and the faintest were sixth magnitude. Centuries later we still use this scale although it has since been modernized How Science Works: Research into how a star’s colour is linked to its surface temperature. Preparing for the next lesson: Brightness of ______ are assigned a number starting with the brightest star starting at about -1 magnitude. Dimmer stars are _____ or positive numbers. The larger the number means the _______ the star is. For example, a star -1 magnitude is _______ than a star 0 magnitude. Decide whether the following statements are true or false : False True 3: The Sun is an average star with a average size and luminosity ? False True 2: Stars further way from Earth have on average lower actual brightness ? False True 1: A stars luminosity depends on its name and size ?