the properties of stars. stars at night when the sun sets, and the moon is not out we quickly...
TRANSCRIPT
The Properties of StarsThe Properties of Stars
Stars at NightStars at Night
When the sun sets, When the sun sets, and the Moon is and the Moon is not out we quickly not out we quickly discover that our discover that our sky is filled with sky is filled with many thousands of many thousands of stars.stars.
Stars at NightStars at Night
Constellations, Constellations, such as the such as the Pleiades, are seen Pleiades, are seen throughout the sky.throughout the sky.
Stars at NightStars at Night
Upon closer Upon closer examination we examination we discover that these discover that these stars emit different stars emit different levels and colours levels and colours of light.of light.
Take the stars in Take the stars in the constellation the constellation Orion for example.Orion for example.
LightLight
We are able to see We are able to see these colourful these colourful stars because of stars because of the light they emit.the light they emit.
But what is light?But what is light?
LightLight
Light is a form of Light is a form of energy.energy.
It travels in a It travels in a straight line unless straight line unless affected by affected by extreme gravity. extreme gravity.
Like water, it Like water, it travels in travels in wavelengths.wavelengths.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
There are many forms of light.There are many forms of light. All of them, including visible light, All of them, including visible light,
are a form of electromagnetic are a form of electromagnetic radiation.radiation.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
All of the different forms of All of the different forms of electromagnetic radiation (light) can be electromagnetic radiation (light) can be placed on a chart or spectrum.placed on a chart or spectrum.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
Stars give off all these different forms of Stars give off all these different forms of light.light.
Our eyes, and light collecting telescopes, Our eyes, and light collecting telescopes, can only see a very small portion of the can only see a very small portion of the spectrum called visible light.spectrum called visible light.
Star BrightnessStar Brightness
Star brightness is dependant on Star brightness is dependant on three things:three things:• ProximityProximity• TemperatureTemperature• Size/MassSize/Mass
Star Brightness-ProximityStar Brightness-Proximity
Imagine a car was parked on a hill Imagine a car was parked on a hill one kilometer from you.one kilometer from you.
At the same time a friend was At the same time a friend was standing next to you with a small standing next to you with a small pocket flashlight.pocket flashlight.
Each light was shone in your eyes.Each light was shone in your eyes. Which would appear brighter?Which would appear brighter? Which is really brighter?Which is really brighter? Star brightness works the same way.Star brightness works the same way.
Star Brightness-ProximityStar Brightness-Proximity
The actual The actual brightness of a star brightness of a star is dependant on is dependant on how much energy how much energy it emits.it emits.
Its apparent Its apparent brightness is brightness is determined by this determined by this factor but also how factor but also how far or close it is to far or close it is to Earth.Earth.
Star Brightness-TemperatureStar Brightness-Temperature
Temperature can Temperature can affect brightness.affect brightness.
Which has the Which has the highest highest temperature:temperature:• A light bulb A light bulb
filament.filament.• A heating element.A heating element.
Star Brightness-TemperatureStar Brightness-Temperature
Different temperature stars have Different temperature stars have different brightness.different brightness.
The hotter the star the brighter the The hotter the star the brighter the star.star.
Star Brightness-ColourStar Brightness-Colour
Temperature also affects the colour Temperature also affects the colour of a star.of a star.
The cooler the star the closer it is to The cooler the star the closer it is to red in colour.red in colour.
The hotter the star the closer it is to The hotter the star the closer it is to blue-white in colour.blue-white in colour.
Star Brightness-ColourStar Brightness-Colour
Betelgeuse, a red Betelgeuse, a red giant, has a lower giant, has a lower temperature (and temperature (and therefore therefore brightness) than brightness) than our sun.our sun.
Star Brightness-ColourStar Brightness-Colour
Rigel, a large white Rigel, a large white supergiant, is not supergiant, is not only large but only large but extremely hot.extremely hot.
It is therefore It is therefore extremely bright.extremely bright.
Hang on…Hang on…
Let’s not get ahead Let’s not get ahead of ourselves.of ourselves.
Turn to page 462 Turn to page 462 and …and …
Star Temperature-ColourStar Temperature-Colour
As we have seen star temperature As we have seen star temperature can affect brightness.can affect brightness.
Different star types also have Different star types also have different temperatures.different temperatures.
They can be linked to colour.They can be linked to colour.
Star Temperature-ColourStar Temperature-Colour
Generally speaking Generally speaking red stars have the red stars have the lowest lowest temperatures while temperatures while blue-white stars blue-white stars are the hottest.are the hottest.
Star Colour and CompositionStar Colour and Composition
While colour can tell us about While colour can tell us about brightness and temperature it can brightness and temperature it can also tell us what a star is made of.also tell us what a star is made of.
To do this they use something called To do this they use something called a spectroscope.a spectroscope.
Star Colour and CompositionStar Colour and Composition
A spectroscope A spectroscope acts like a prism, acts like a prism, dividing light into dividing light into the different the different spectral colours.spectral colours.
Star Colour and CompositionStar Colour and Composition
When light leaves a When light leaves a star it passes star it passes through the through the elements in the elements in the star.star.
This leaves This leaves darkened lines on darkened lines on the spectrum of the spectrum of light as some of light as some of the elements block the elements block out that light.out that light.
ActivityActivity
Turn to page 465 in your text and Turn to page 465 in your text and read the instructions with your read the instructions with your teacher, then complete the analysis teacher, then complete the analysis questions.questions.
Star Size and MassStar Size and Mass
Stars come in many different sizes.Stars come in many different sizes. Star size is measured once we know Star size is measured once we know
the distance to the star from Earth. the distance to the star from Earth. (This is done using something called (This is done using something called parallax.)parallax.)
Combining this knowledge with the Combining this knowledge with the brightness and temperature of the brightness and temperature of the star astronomers can deduce the size star astronomers can deduce the size of the star.of the star.
Star SizeStar Size
Our sun is the Our sun is the baseline. baseline.
Other stars can be Other stars can be as small as 0.1 the as small as 0.1 the radius of our sun or radius of our sun or as large as 1000 as large as 1000 times as large.times as large.
Star SizeStar Size
Arcturus is a red giant and the third Arcturus is a red giant and the third brightest star in the sky.brightest star in the sky.
Star SizeStar Size
VY Canis Majoris is VY Canis Majoris is the largest known the largest known star in the star in the universe.universe.
Star MassStar Mass
For many years there was no way to For many years there was no way to calculate the mass of any star, even calculate the mass of any star, even our sun.our sun.
In order to calculate the mass of a In order to calculate the mass of a large object (like a star) you need to large object (like a star) you need to see how gravity affects it.see how gravity affects it.
Stars are so big that they are not Stars are so big that they are not affected by the gravity of planetary affected by the gravity of planetary objects.objects.
Star MassStar Mass
What was needed What was needed was another large was another large object close to a object close to a star, such as star, such as another star.another star.
Binary StarsBinary Stars
A binary star is a A binary star is a star system where star system where two stars orbit one two stars orbit one another.another.
Their orbits allow Their orbits allow astronomers to astronomers to calculate the mass calculate the mass by observing how by observing how the gravity of one the gravity of one affects the gravity affects the gravity of the other.of the other.
Solar MassSolar Mass
Star mass is Star mass is expressed as solar expressed as solar mass.mass.
The Sun has a solar The Sun has a solar mass of 1.mass of 1.
All the others are All the others are compared to the compared to the sun.sun.
Putting It All TogetherPutting It All TogetherThe Hertzsprung-Russell DiagramThe Hertzsprung-Russell Diagram
To make sense of To make sense of all this two all this two astronomers, Enjar astronomers, Enjar Hertzsprung and Hertzsprung and Henry Norris Henry Norris Russell devised a Russell devised a diagram to better diagram to better explain it.explain it.
The Hertzsprung-Russell DiagramThe Hertzsprung-Russell Diagram
The Hertzsprung-Russell DiagramThe Hertzsprung-Russell Diagram
Scientists began to Scientists began to notice something notice something about the diagram.about the diagram.
Most stars fit in the Most stars fit in the center. They were center. They were referred to as main referred to as main sequence stars.sequence stars.
The Hertzsprung-Russell DiagramThe Hertzsprung-Russell Diagram
Other stars were Other stars were outside this main outside this main sequence.sequence.
Why?Why? Were they special Were they special
in some way?in some way? Exceptions to the Exceptions to the
rule?rule?
HomeworkHomework
Please read all of section 14.1, from Please read all of section 14.1, from pages 462 to 467.pages 462 to 467.
Answer questions 1-6 on p.467Answer questions 1-6 on p.467 VocabularyVocabulary
• Electromagnetic SpectrumElectromagnetic Spectrum• Binary starsBinary stars• Solar MassSolar Mass
Homework to Hand InHomework to Hand InPage 466-467Page 466-467
Please complete a hand drawn and Please complete a hand drawn and coloured version of the Hertzprung-Russell coloured version of the Hertzprung-Russell Diagram. Diagram.
Your diagram should be neatly presented Your diagram should be neatly presented on unlined paper. Don’t forget to clearly on unlined paper. Don’t forget to clearly label each axis and have the diagram label each axis and have the diagram coloured.coloured.
With your diagram you need to include an With your diagram you need to include an explanation (approximately 1-2 explanation (approximately 1-2 paragraphs), in your own words of how the paragraphs), in your own words of how the diagram works.diagram works.