star properties star types h-r diagram -...
TRANSCRIPT
Study Points• Define luminosity and brightness.
• When you see a bright star, can you tell if it is luminous? If it is
close? Explain.
• Describe how astronomers measure the distance to a nearby star.
• Describe how to use brightness and luminosity to find the distance
to a star.
• What is an H-R diagram? Sketch one. Given the position of a star
on the H-R diagram, indicate if the star is hot or cold, luminous or
not.
• Roughly describe the luminosity, surface temperature, and size of
the following types of stars: main sequence, giant, supergiant,
white dwarf, & red dwarf. Which are the most common?
• Why are supergiant stars rare?
• Know the comparison of mass and lifetime of main sequence, giant,
supergiant, white dwarf, & red dwarf stars. Which live the shortest
lives? Which live the longest lives?
Brightness (B) and Luminosity (L)
Distance to a star (D)
Star sizes
H-R diagram
Luminosity vs Temperature
Some star types
Star Properties
Brightness, B
• *Measure of energy received from a star
– Defined by magnitude
• Brightness = Magnitude (visual scale)
– from Hipparchus: 1(bright) to 6(faint)
– Now -1.5 Sirius to faint stars at 6+
Luminosity, L
• *Measure of energy emitted by a star
– Energy per second (Watts)
• *Useful symbol, L
– Luminosity of our sun
Light bulb
• Brightness and Luminosity
• Ex – Two 40 watt bulbs.
– One here and one at Subway across the street.
• Which is more luminous?
–Energy emitted
• Which is brighter?
–Energy received
Light bulb
• Brightness and Luminosity
• Ex – Two 40 watt bulbs.
– One here and one at Subway across the street.
• Which is more luminous?
–Energy emitted
• Which is brighter?
–Energy received
• Same
• Closer one
Light bulb
• Brightness or luminosity
• Back to 40 watt bulb
• Walk farther down street with it.
• Brightness depends on distance
• Compare with other light bulbs
– Different watts
Bright stars? Magnitude? Very Luminous stars?
Bright stars are: ______________ or ______________
Bright stars are:
more distant and very luminous
ORcloser (shorter distance) and not so luminous
DL
DL
*Brightness, B depends on:
Luminosity, L
Distance, D
2D
LkB =
Sirius: B?
Sirius: B L?
Sirius: B L?
Close (8.6 LY)
Sirius: B L
Close (8.6 LY)
Average
luminosity
( 33 L
)
Sirius is BRIGHT (-1.46) because it is CLOSE, not because it
has a high luminosity.
Betelgeuse: B?
Betelgeuse: B L?
Betelgeuse: B L?
Far (429 LY)
Betelgeuse: B L
Far (429 LY)
Very Luminous!
(330,000 L
)
Betelgeuse is BRIGHT because it is VERY LUMINOUS.
It is not close.
Finding distances to stars
• *Use parallax and
trigonometry on nearby
stars to get distance
(valid for few hundred LY)
Finding distances to stars
2D
LkB =
For those same nearby stars
• Know D
• Measure B
• Then calculate L
*Finding distances to stars!!
• Type of star gives you L
• Measure B
• Calculate D
• To read more about L
and types of stars see
Henrietta Levitt
• Watch (1:00):• https://scientificwomen.net/wome
n/leavitt-henrietta-55
2D
LkB =
*H-R
DiagramHertzsprung-Russell
*Star
Luminosity
vs.
Surface
Temperature
*H-R
Diagram
*Star
Luminosity
vs.
Surface
Temperature
H-R Diagram
1. Which star is hotter?
2. Which star is more luminous?
Why?
H-R Diagram
1. Which star is hotter?
2. Which star is more luminous?
Why?
SAME (COLOR)
LARGER STAR
BECAUSE IT IS LARGER
H-R Diagram
3. Which star is hotter?
4. Which star is more luminous?
Why?
H-R Diagram
3. Which star is hotter?
4. Which star is more luminous?
Why?
WHITE STAR
SAME SIZE BUT
WHITE IS MORE LUMINOUS
LUMINOSITY DEPENDS ON
TEMPERATURE AND RADIUS
H-R Diagram
5. Which star is hotter?
6. Which star is more luminous?
Why?
H-R Diagram
5. Which star is hotter?
6. Which star is more luminous?
Why?
BLUE STAR
BLUE STAR
LUMINOSITY DEPENDS ON
TEMPERATURE AND RADIUS
H-R Diagram
Luminosity depends on…
Temperature and Size (Radius)
H-R Diagram
Which star type can be
hot but not luminous?
Which star type can be
cool but is luminous?
Graphing T vs L tells us the size of the star
H-R Diagram
Which star type can be
hot but not luminous?
Which star type can be
cool but is luminous?
Graphing T vs L tells us the size of the star
WHITE
DWARF
RED
SUPERGIANT
Sizes of stars
https://www.youtube.com/watch?v=cMWMtLGGg6o
Sizes of starshttps://en.wikipedia.org/wiki/List_of_largest_stars
*H-R
Diagram
Main Sequence
• ~80% of all stars: most common*
• Long lived - Sun ~1 X 1010 yrs
• Average, middle class stars
• ~0.1 to 10 R
• ~average masses
Main Sequence
• Ex: Sun,
Sirius A,
Procyon A,
Alpha Centauri A
Giants (Often red giants)
• Rare
• Shorter lived
• ~1 - 5 M
• ~10 to 100 R
Giants
Ex: Arcturus,
Aldebaran,
Spica
Giants
Ex: Arcturus,
Aldebaran,
Spica
Giants
Ex: Arcturus,
Aldebaran,
Spica
Red
Giants
Blue
Giants
Supergiants• Very rare
• Shortest lived
– Few exist at any given time due to “short” life*
• ~ 5 to 100 M
• ~ 10 to 1000 R
• Ex: Betelgeuse -- Orbit of Mars or Jupiter
Super-
giantsEx:
Cephei
Orbit of
Jupiter
White Dwarf
• Mass ~ M
• Size ~ Earth (0.01 R
)
• One teaspoon weighs ~one ton
• Extremely long lives
• Ex: Sirius B
Red Dwarf
• Smaller, cooler version of sun
(Not a cooler
white dwarf)
• Many
• M ~ 0.1 M
• R ~ 0.1 R
• L ~ 1/2000 L
• Ex: Proxima Centauri
• Extremely long lives
Rho Ophiuchi has 30+ Red dwarfs
Black Dwarf
• Theoretical
• None found yet
• Cold & dark (still warmer than space)
• Cooled down white dwarf
• Our universe may not be old enough yet to
have any black dwarfs.
H-R Diagram
Brown Dwarf
• Not on HR diagram
• Size ~ Jupiter (~1/10 R
)
• Mass ~ 1/100 M
• Failed star (planet?)
• 10-100 times more
massive than Jupiter
Star Life Summary*
SHORTEST LIFE and LARGEST MASS
• Supergiants – shortest lives; ~3–50 million years
• Giants – shorter lives; ~100 million years
• Main Sequence – long lives; billions of years
• White & Red Dwarfs – longest lives; hundreds of
billions of years or trillions of years (maybe to the life of a
proton 1032 or more)
LONGEST LIFE and SMALLEST MASS
KNOW THE ORDER.
Don’t need to know
numbers.
Brightness and Luminosity
Distance to star
B depends on L and D
H-R diagram (Plot of L vs T)
Types of stars (Main sequence,
Giants, Supergiants, White dwarfs,
Red dwarfs, Brown dwarfs)
Summary
Homework & Updates• Keep up with Study Points
• Astronomy Crash Course #26 about Stars:
https://www.pbs.org/video/crash-course-astronomy-26/
• D2L Quiz 9 & 10 available; Quizzes 9-13 for Test 3
• Lab Update – last lab this week on Lenses & Telescopes• Open notebook Lab Test coming up on Nov. 19 & 21
• Lab Test preparation in lab this week
• Observations:• Astrophysics Lecture Due Dec. 3 (10 pts) Write report (Lecture done 10/10)• Astronomy News Evalution Due Dec. 10 (20 pts) Evaluate astronomy news• Planetarium Due Dec. 3 (10 pts) Go to a planetarium show (Field trip 10/3)• Stargazing Due Dec. 17 (20 pts) Go stargazing & write report• Telescope Due Dec. 17 (20 pts) Look through a telescope
• Look at calendar options & weather• Moon Craters Due Dec. 17 (10 pts) Look at magnified moon craters
• Borrow binoculars from Lab room
Astronomy Crash Course #26 about
Stars (also on YouTube):
https://www.pbs.org/video/crash-
course-astronomy-26/