Characteristics of StarsCharacteristics of Stars

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Characteristics of StarsCharacteristics of Stars

The Sun is an average star:The Sun is an average star:

it’s not hot or coolit’s not hot or cool

it’s not large or small.it’s not large or small.

We can compare stars by colour, We can compare stars by colour, temperature, size, brightness temperature, size, brightness and spectrum.and spectrum. P.458P.458

The Sun is larger than 95% of the The Sun is larger than 95% of the stars.stars.

Dwarf Star SunDwarf Star Sun Giant Star Giant Star Super Giant Star Super Giant Star

Colour and TemperatureColour and Temperature

Colour:Stars range in colour from red, orange, yellow, Stars range in colour from red, orange, yellow,

white, to blue.white, to blue.

Red ----------- Yellow (Sun) ----------- > BlueRed ----------- Yellow (Sun) ----------- > Blue

Temperature:Stars range in temperature from 2000Stars range in temperature from 2000ooC--50 C--50

000000ooC.C.

2 0002 000ooC ---------5 000C ---------5 000ooC (Sun)--------- > 50 000C (Sun)--------- > 50 000ooCC

Colour and TemperatureColour and Temperature

Colour and temperature are Colour and temperature are linked.linked.

The 2000The 2000ooCC stars are stars are redred in colour. in colour.

The 50 000The 50 000ooCC stars are stars are blueblue in in colour.colour.

Colour and TemperatureColour and TemperatureColour Temp. Range

(oC)Examples

Blue 25000 – 50 000 Zeta OrionisZeta Orionis

Bluish-white 11 000 – 25 00011 000 – 25 000 Rigel, SpicaRigel, Spica

White 7 500 - 11 0007 500 - 11 000 Vega, SiriusVega, Sirius

Yellowish-white 6 000 - 7 5006 000 - 7 500 Polaris, ProcyonPolaris, Procyon

Yellow 5 000 - 6 0005 000 - 6 000 Sun, Alpha CentauriSun, Alpha Centauri

Orange 3 500 - 5 0003 500 - 5 000 Arcturus, AldebaranArcturus, Aldebaran

Red 2 000 - 3 5002 000 - 3 500 Betelgeuse, Betelgeuse, AntaresAntares

BrightnessBrightness

Brightness is related to the Brightness is related to the distance from the earth and the distance from the earth and the age of the star.age of the star.

Hipparchus developed the idea of Hipparchus developed the idea of classifying stars by their brightness.classifying stars by their brightness.

11stst magnitude stars are the magnitude stars are the brightestbrightest

66thth magnitude stars are the weakest magnitude stars are the weakest

Apparent MagnitudeApparent Magnitude – refers to the – refers to the brightness of a star as it appears to brightness of a star as it appears to us.us.

Absolute MagnitudeAbsolute Magnitude – refers to the – refers to the actual amount of light given off by a actual amount of light given off by a star at a standard distance.star at a standard distance.

SpectrumSpectrum

Spectroscope:Spectroscope: Used to measure the Used to measure the chemical composition of the stars. chemical composition of the stars. (also temperature and direction the (also temperature and direction the star is moving in relation to the star is moving in relation to the Earth.)Earth.)

How? Set up a spectroscope with How? Set up a spectroscope with different tubes; each gas has different tubes; each gas has different spectras – light patterns.different spectras – light patterns.

Questions - P. 460Questions - P. 4601.1. How is the colour of a star related to its How is the colour of a star related to its

temperature?temperature?The colour of a star depends on its temperature, The colour of a star depends on its temperature,

from red and orange (cool stars) to yellow and from red and orange (cool stars) to yellow and white (hotter stars) to blue (very hot stars).white (hotter stars) to blue (very hot stars).

2. 2. Explain why a cooler star could actually Explain why a cooler star could actually appear brighter than a hotter star.appear brighter than a hotter star.

A cool star, such as a red giant, could be either A cool star, such as a red giant, could be either closer to us or much larger than a hotter star, closer to us or much larger than a hotter star, such as a white dwarf. (Could be closer and such as a white dwarf. (Could be closer and larger)larger)

Final 30 minutes of classFinal 30 minutes of class

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Quiz: Video quiz and MC (20 marks)Quiz: Video quiz and MC (20 marks)