Transcript – HR diagram Classification of Stars Objectives:
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 52-54 worksheet, 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”?
Low Energy High Energy wavelength R O Y G B I V
Star Color and Temperature Yellow Blue RED 2,500 Cool stars Long wave lengths 6,000 30,000 K Hot stars Short wavelengths R O Y G B I V
Measuring the Brightness of a Star “Stellar Brightness” Magnitude – the brightness of a star Magnitude is measured using (-) and (+) numbers the more (-) the number, the brighter the more (+), the dimmer the 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 ?
Apparent Magnitude of various objects
bright dim OBJECT
SUN
Full Moon Venus Sirius
North Star
Naked eye
Pluto HST
Apparent Magnitude -26.5 -12.5
- 4.1
-1.4
2.0
6.0
15 28
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:
Apparent Magnitude
bright
-26.7
Earth
Absolute magnitude
dim +5 32.6 ly
Distance, Apparent Magnitude, and Absolute Magnitude of Some Stars View from Earth 32.6 ly
Name Distance Light-years Apparent Magnitude Absolute Magnitude Sun Alpha Centauri NA 4.27
-26.7
0.0
5.0
4.4
Sirius Arcturus Betelgeuse Deneb 8.70
36 520 1600 -1.4
-0.1
.08
1.3
1.5
-0.3
-5.5
-6.9
So, which star is biggest to smallest?
Brightness scale – Using Absolute Magnitude -7 -5 Bright -3 -1 0 1 3 5 7 Dim 9
The brighter, the bigger the star
How are stars classified? – the Hertzsprung-Russell Diagram (HR-diagram) -10 O B A F G K M Very Bright -5 0 +5 +10 Very Dim +20 20,000 14,000 10,000 7000 5000 Surface Temperature (K) 3000
Spectral class: based on their spectrum (color they emit resulting from the chemical make-up) O B A F G K M O
h
, B
e
A F
ine
G
uy
(or G
al
), K
iss
M
e
O
0
O
1
…..O
9
B
0
…..B
9
A
0
…..A
9 Hottest
F……………
Coolest
HR-Diagram Cool, bright Hot, dim 20,000 14,000 10,000 7000 5000 Surface Temperature (K) 3000
O B A F G K M
Stellar evolution HR-Diagram Variable Star stage Red Giant Stage Planetary Nebula Stage Main Sequence Star Protostar Dust and gasses White Dwarf Black Hole Stage 20,000 14,000 10,000 7000 5000 Surface Temperature (K) 3000