classification of stars – hr diagram objectives: understand the differences between near and...
TRANSCRIPT
Classification of Stars – HR diagram
Objectives:• understand the differences between near and bright visible stars
• learn how to use the HR-diagram to classify stars (temperature vs. brightness)
• use the HR-diagram to observe the evolution of stars (when a star is born and dies)
Lab Books:pages 52-54worksheet, page 115
Lab Books:pages 52-54worksheet, page 115
HR-diagram – classifies stars using temperature magnitude (brightness)HR-diagram – Hertzbrung-Russell diagram
Star color and Temperature
Lets review the visible color spectrum.“What do our eyes see”?
wavelength
R O Y G B I V
Low Energy High Energy
Star Color and TemperatureStar Color and Temperature
R O Y G B I V R O Y G B I V
30,000 K2,500 6,000
Long wave lengths Short wavelengths
Cool stars Hot stars
REDYellow Blue
Measuring the Brightness of a Star“Stellar Brightness”
Magnitude – the brightness of a star
Apparent Magnitude• a stars brightness as it appears from earth
• factors controlling apparent magnitude:
• how big the star• how hot the star• how far away star
Which is brighter? -5 star or 5 star ?
Magnitude is measured using (-) and (+) numbers
the more (-) the number, the brighter the more (+), the dimmer the star
SUNFull
Moon Venus SiriusNorthStar
Nakedeye
Pluto HSTOBJECT
ApparentMagnitude -26.5 -12.5 - 4.1 -1.4 2.0 6.0 15 28
Apparent Magnitude of various objects
bright dimdim
Absolute Magnitude• measures the “actual” brightness• two stars with the same absolute magnitude would not be the same apparent magnitude
WHY?• To compare absolute brightness
• use a standard distance of 32.6 light-years away from earth
Example:
-26.7 +5
32.6 ly
Apparent Magnitude Absolute magnitude
Earth
bright dim
Distance, Apparent Magnitude, and AbsoluteMagnitude of Some Stars
Name DistanceLight-years
ApparentMagnitude
AbsoluteMagnitude
Sun NA -26.7 5.0
Alpha Centauri 4.27 0.0 4.4
Sirius 8.70 -1.4 1.5
Arcturus 36 -0.1
-5.5
-0.3
Betelgeuse 520 .08
Deneb 1600 1.3 -6.9
32.6 lyView from Earth
So, which star is biggest to smallest?
Brightness scale – Using Absolute Magnitude
The brighter, the bigger the starThe brighter, the bigger the star
0 1 3 5 7 9
Bright Dim
-1-3-5-7
SunSun
Centa
uri
Centa
uri
Sirius
Sirius
Arctu
rs
Arctu
rs
Betel
geuse
Betel
geuse
Deneb
Deneb
Surface Temperature (K)30005000700010,00014,00020,000
How are stars classified? – the Hertzsprung-RussellDiagram (HR-diagram)
-10
-5
0
+5
+10
+20
Ab
solu
te M
ag
nit
ud
e
Very Bright
Very Dim
O B A F G K M
Oh, Be A Fine Guy (or Gal), Kiss MeOh, Be A Fine Guy (or Gal), Kiss Me
O0O1…..O9 B0…..B9 A0…..A9 F……………HottestHottest CoolestCoolest
Spectral class: based on their spectrum (color they emit resulting from the chemical make-up)Spectral class: based on their spectrum (color they emit resulting from the chemical make-up)
O B A F G K MO B A F G K M
HR-Diagram
Surface Temperature (K)30005000700010,00014,00020,000
Cool, brightCool, bright
Hot, dimHot, dim
The Brighter, The Hotter
The cooler, the dimm
er
OO BB AA FF GG KK MM
Surface Temperature (K)30005000700010,00014,00020,000
Dust andgassesProtostar
Main SequenceStar
Red GiantStage
VariableStar stage
PlanetaryNebulaStage
White DwarfBlack
Hole Stage
Stellar evolution HR-Diagram